EFFECTS OF LYGUS HESPERUS (KNIGHT) ON GROWTH, YIELD, AND QUALITY OF COTTON

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1 EFFECTS OF LYGUS HESPERUS (KNIGHT) ON GROWTH, YIELD, AND QUALITY OF COTTON Item Type text; Dissertation-Reproduction (electronic) Authors Jubb, Gerald Lombard, Publisher The University of Arizona. Rights Copyright is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 02/05/ :37:57 Link to Item

2 \ JUBB, Jr.. Gerald Lombard, EFFECTS OF LYGUS HESPERUS KNIGHT ON GROWTH s YIELD, AND QUALITY OF COTTON. University of Arizona, Ph.D., 1970 Entomology University Microfilms, A XERQK Company, Ann Arbor, Michigan THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED

3 EFFECTS OF LYGUS HESPERUS KNIGHT ON GROWTH, YIELD, AND QUALITY OF COTTON by Gerald Lombard Jubb, Jr. A Dissertation Submitted to the Faculty of the DEPARTMENT OF ENTOMOLOGY In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA

4 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE I hereby recommend that this dissertation prepared under my direction by Gerald L. Jubb, Jr. entitled EFFECTS OF LYGUS HESPERUS KNIGHT ON GROWTH, YIELD, AND QUALITY OF COTTON be accepted as fulfilling the dissertation requirement of the degree of Doctor of Philosophy Dissertation Director ^JJate After inspection of the final copy of the dissertation, the following members of the Final Examination Committee concur in its approval and recommend its acceptance:" J -9. ^ v. / C /??< 'on* AC /9*Q ^ HT ;./V7ft ^ J 7-1^~ /. Q^tC^-<, r^~, It? 13 ''This approval and acceptance/is contingent on the candidate's adequate performance and defense of this dissertation at the final oral examination. The inclusion of this sheet bound into the library copy of the dissertation is evidence of satisfactory performance at the final examination.

5 STATEMENT BY AUTHOR This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona- and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED:

6 To my wife, Carole, arid to our parents iii

7 ACKNOWLEDGMENTS I extend sincere appreciation to my major professor, Dr, L. A. Carruth, whose guidance, interest, and encouragement have helped 1 to make this dissertation possible. Gratitude is expressed to Dr, W. L. Nutting, Dr, G. W, Ware, and Dr. T. F. Watson, Department of Entomology, and Dr, M, A. McClure and Dr. E. L, Nigh, Jr., Department of Plant Pathology, for their useful comments during the review of the manuscript. Dr, L, S. Stith, Department of Plant Breeding, and Professor H, N. Stapleton, Department of Agricultural Engineering, are acknowledged for their assistance in interpreting plant growth data. I thank Dr. A. B. Humphrey, Biometrician, College of Medicine, formerly Statistician, Arizona Agricultural Experiment Station, for his guidance regarding experimental design. I also express appreciation to Dr, J, Gebert, Statistician, Arizona Agricultural Experiment Station, and Dr. G. D. Butler, Jr., U.S. Department of Agriculture, Cotton Insects Laboratory, Tucson, for their advice concerning statistical procedures. iv

8 TABLE OF CONTENTS Page LIST OF TABLES LIST OF ILLUSTRATIONS. ABSTRACT... r vii x xiii INTRODUCTION,. 1 LITERATURE REVIEW 3 Damage to Cotton by Lygus spp 3 Lygus Feeding Lygus Damage to Other Crops 10 MATERIALS AND METHODS * Type of Experiment and Design 14 Cage Construction Source and Identification of Lygus hesperus., 20 Collection of Data Growth and Fruiting Characteristics 22 Yield and Quality Measurements 23 Lygus Feeding Experiment Effect of Cages Climatological Data Statistical Procedures. 30 RESULTS.33 Plant Heights and Structure 33 Patterns of Square Production. 42 Patterns of Flower Production 53.Patterns of Boll Production.. 65 Boll Setting 72 Shedding of Fruiting Bodies 82 Square Shedding 82 Boll Shedding Yield Characteristics. 92 Lint Quality and Value 103 Lygus Feeding Experiment v

9 vi TABLE OF CONTENTS (Continued) Page DISCUSSION, SUMMARY 122 CONCLUSIONS.., APPENDIX A; 1969 CLIMATOLOGICAL DATA 127 APPENDIX B; ANALYSIS OF VARIANCE TABLES 129 APPENDIX C; WEEKLY TOTALS OF FLOWERS PRODUCED PER TREATMENT 131 APPENDIX D: CUMULATIVE PERCENTAGE OF THE TOTAL FLOWERS PRODUCED 133 APPENDIX E: CRITICAL VALUES OF D FOR KOLMOGOROV-SMIRNOV 2-SAMPLE TEST APPENDIX F; CUMULATIVE NUMBER OF OPEN BOLLS APPENDIX G; CUMULATIVE PER CENT OF THE TOTAL OPEN BOLLS 139 APPENDIX H: WEEKLY TOTALS OF FLOWERS THAT SET BOLLS ' 141 APPENDIX Is CUMULATIVE PER CENT OF FLOWERS THAT SET BOLLS 143 LITERATURE CITED 145

10 LIST OF TABLES Table Page 1. Identification of main factors and their levels 16 2, Treatments produced by combination of the various levels of the main factors Weekly mean increase in plant height (cm) for noninfested control plants and plants infested with one nymphal or adult male k* hesperus during four infestation periods Mean plant height (cm) on Sept. 18, 1969r following infestation by one nymphal or adult male L. hesperus during four infestation periods Mean number of main stem nodes and vegetative and fruiting branches on noninfested caged cotton plants and on plants exposed to one nymphal or adult male L. hesperus during four infestation periods Linear regression and correlation analysis for square production from June 12 to July Dates for each week of flowering Summary of mean total flowers produced per plant at the end of the sixth and twelfth weeks of flowering after exposure to one nymphal or adult male L. hesperus during four infestation periods Linear regression and correlation analysis of weekly flower production data for infested and noninfested caged plants vii

11 LIST OF TABLES (Continued) Table Page 10. Mean percentage of flowers per plant that set bolls after exposure to one nymphal or adult male L. hesperus during four infestation periods Square abscission, expressed as percentages of estimated total weekly square production Mean yields of seed cotton (grams) per plant after exposure to one nymphal or adult male L. hesperus during four infestation periods * Mean yield of lint (grams) per plant after exposure to one nymphal or adult male L. hesperus during four infestation periods Estimated yields on a per acre basis Mean number of bolls picked per plant after exposure to one nymphal or adult male L. hesperus during four infestation periods Mean lint percentage per plant following infestation by one nymphal or adult male L, hesperus during four infestation periods Mean seed index (grams/100 seeds), per plant after exposure to one nymphal or adult male L. hesperus during four infestation periods Monetary values (cents/lb.) of lint produced per plant after exposure to one nymphal or adult male L. hesperus during four infestation periods Days from time of feeding by L. hesperus to time of square abscission

12 if, ix LIST OF TABLES (Continued) Table Page 20. Lygus hesperus feeding times on cotton , Sununary of results 123

13 LIST OF ILLUSTRATIONS Figure Page % 1. Field layout of infested and noninfested control (C) cages in the lygus damage experiment Weekly mean heights of noninfested caged cotton plants and nearby noncaged plants Weekly mean heights (cm) of cotton plants exposed to one nymphal or adult male hesperus during the (A)" entire and TB) early infestation periods Weekly mean heights (cm) of cotton plants exposed to one nymphal or adult male hesperus during the (A) mid and (B) late infestation periods Squaring patterns of caged and noncaged control plants Squaring patterns of plants exposed to one nymphal or adult male L. hesperus during the entire infestation period Squaring patterns of plants exposed to one nymphal or adult male L. hesperus during the early infestation period Squaring patterns of plants exposed to one nymphal or adult male L. hesperus during the mid infestation period 46 ' 9, Squaring patterns of plants exposed to one nymphal or adult male L. hesperus during the late infestation period., Patterns of flower production by caged and noncaged control plants..." 55 x

14 i xi LIST OF ILLUSTRATIONS (Continued) Figure Page 11. Patterns of flower production by plants infested with one nymphal or adult male L. hesperus during the (A) entire and (B) early infestation periods Patterns of flower production by plants infested with one nymphal or adult male L. hesperus during the (A) mid and (B) late infestation periods Cumulative per cent of the total flowers produced on noninfested control plants and on plants exposed to one nymphal or adult male L. hesperus during four infestation periods Patterns of boll opening on caged and noncaged control plants Patterns of boll opening by. plants exposed to one nymphal or adult male L. hesperus during the (A) entire and (B) early infestation periods Patterns of boll opening by plants exposed to one nymphal or adult male L. hesperus during the (A) mid and (B) late infestation periods Cumulative per cent of the total open bolls on noninfested control plants and on plants exposed to one nymphal or adult male L. hesperus during four infestation periods Patterns of boll setting on noninfested caged cotton plants and nearby noncaged plants Patterns of boll setting on plants exposed to one nymphal or adult male L. hesperus during the entire infestation period I 20. Patterns of boll setting on plants exposed to one nymphal or adult male L. hesperus during the early infestation period 76

15 XI1 LIST OF ILLUSTRATIONS (Continued) Figure Page 21, Patterns of boll setting on plants exposed to one nymphal or adult male L, hesperus during the mid infestation period 77 22, Patterns of boll setting on plants exposed to one nymphal or adult male L. hesperus during the late infestation period 78 23, Cumulative per cent of flowers that set bolls on noninfested control plants and on plants exposed to one nymphal or adult male L, hesperus during four infestation periods Patterns of square shedding by noninfested caged cotton plants and by plants exposed to one nymphal or adult male L. hesperus during the (A) entire and (B) early infestation periods Patterns of square shedding by noninfested caged cotton plants and by plants exposed to one nymphal or adult male L, hesperus.during the (A) mid and (B) late infestation periods Patterns of boll shedding by noninfested control plants and by plants exposed to one nymphal or adult male L, hesperus during the (A) entire and (B) early infestation periods Patterns of boll shedding by noninfested control plants and by plants exposed to one nymphal or adult male L. hesperus during the (A) mid and (B) late infestation periods 91

16 ABSTRACT Feeding behavior and plant injury by Lygus hesperus Knight (Hemiptera:Miridae) were studied on cotton, Gossypium hirsutum L,, variety Deltapine 16, at Tucson, Arizona, in Individual plants were caged in the field and subjected to continuous infestations of either one late-instar nymph or one adult male for the 66-day period from first square formation, on June 12, to the last approximate date of effective squaring, arbitrarily selected as August 16, or for one of the three successive 22-day periods comprising this total period. Plant development and fruiting behavior were observed daily. Nymphs caused significant increases in plant height and numbers of vegetative branches. Nymphs and adults each caused alterations in the patterns of square and flower production, particularly when infestations occurred early or extended for the entire treatment period. Square formation on infested plants was either delayed or greatly reduced during June and early July with peak squaring occurring up to 11 days later than on noninfested plants. The production of flowers by infested plants lagged during July but increased during August so that the final numbers of»» «\ xiix

17 xiv flowers produced did not differ significantly from the noninfested control plants. Nymphs also caused retardations in boll opening. None of these altered patterns caused statistically significant differences in yields of seed cotton harvested either on October 4 or November 26, and - it appeared that the plants compensated for the damage inflicted. Nymph-infested plants had significantly higher seed indices (weight per 100 seeds) and significantly lower lint percentages in the harvested cotton, indicating the possibility that nymphs may reduce lint yields. Plants infested with adult males during late July and early August produced lint of lower quality and reduced monetary value. It therefore appeared that nymphs and adults were about equal in ability to cause economic losses to Deltapine 16 cotton by reducing either the quantity or quality of the fiber produced. In a second experiment, single squares on field- grown plants were individually caged with their corresponding leaf and each infested with one nymph or adult (male or female) L. hesperus. Time spent by the insects in feeding, preferred feeding sites, and subsequent fate of the plant fruiting structure were determined. No square abscission from these insect feeding activities was observed. Flower buds were not attacked by either nymphs

18 XV or adults. Leaves, leaf petioles, bracts, and square peduncles were the preferred feeding sites. Square abscission apparently does not occur when these latter structures are attacked. Adult males were observed to feed for a significantly longer time than adult females, which in turn, fed for a significantly longer time than nymphs.

19 INTRODUCTION Several species of lygus bugs, principally Lygus hesperus Knight, attack commercially grown cotton in the irrigated agricultural areas of Arizona during June, July, and early August. Lygus feeding and the resultant loss of plant fruiting bodies may cause reductions in yields and quality of harvested cotton. Insecticides have been regularly recommended and applied on an empirical basis for crop protection although little is known of the true importance of lygus bugs as measured by the infestation thresholds necessary for significant economic damage to cotton. Reevaluation of the status of Lygus as a pest of cotton is needed to more accurately establish realistic thresholds of economic injury. Determining the specific injuries inflicted to the cotton plant by lygus bugs and the subsequent affect on yield and quality is a necessary part of this reevaluation. This is a report of research to determine the amount of injury inflicted to cotton by a uniform and continuous infestation of one L. hesperus per plant maintained during the approximate period of effective squaring and during each of three equal portions of this total period. This 1

20 2 injury was evaluated in relation to final yield and quality. The specific objectives of this research were (1) to measure the effects of L. hesperus feeding on plant height and structure, on patterns of square, flower, and. boll production, and on the yield, quality, and monetary value of the harvested lint, (2) to determine the importance of the time of injury and the comparative ability of lateinstar nymphs and adult males to cause plant damage, (3) to observe effects of lygus feeding on subsequent abscission of squares, and (4) to determine preferred feeding sites and times of nymphal and adult feeding at these sites.

21 LITERATURE REVIEW * Damage to Cotton by Lygus spp. In 1918, Morrill reported that Lygus hesperus and- L. lineolaris were the "most destructive pests of cotton in Arizona". These species were first observed damaging cotton in the Salt River Valley in August McGregor (1927) reported that damage by L. lineolaris to cotton in Arizona and California was characterized by perforations on the pistils and anthers of the squares; the carpels and embryonic seeds within the bolls were punctured, eventually leading to cellular proliferations. He concluded that injury was caused by injection of some toxic fluid or an organism during feeding. Ewing (1929), working in Louisiana, published re~ suits of an experiment describing lygus damage to caged cotton plants. His cages, large enough to cover three plants, included some infested with L. lineolaris and L. apicalis introduced weekly for nine weeks. Noninfested control cages were used for comparisons. The plants were examined weekly to observe resulting damage, including square shedding and blasting, lesions on stems and petioles, and mutilation of leaves. Infested plants shed a greater number of squares and were approximately 43 cm shorter 3

22 4 than non-infested plants. Lesions became noticeable 1-4 days after feeding and ranged from the size of a pinhead to over 2 mm long. Lesions occasionally split, exposing a tan colored, granular interior. He did not report or discuss effects of infestations on yields and lint quality. King and Cook (19*32) described lesions formed on stems and petioles after feeding by L. lineolaris. They reported that damage was caused by injected substances toxic to the plant and that squares were shed only when fed. on directly or attacked within a "very short distance" of the squares. Ewing and McGarr (1933) studied caged infestations of L. lineolaris, equivalent to "heavy field infestations", in Louisiana from June 30 to August 4 with plant examinations at 2-3 day intervals. They reported that lygus caused shedding of many squares, production of fewer bolls, and plants averaging approximately 43 cm shorter than control plants. This agreed with earlier results (Ewing 1929). They further reported that infested plants were bushy with erratic branching and an excess of foliage. Although yield and quality measurements were not reported, lygus infested plants lost almost all their fruiting structures. These authors state that the "economic importance of insects that feed on the cotton plant is measured by their effect in keeping the plant from producing and maturing a

23 5 full crop of cotton," They imply that L. lineolaris is of definite economic importance. In Africa, Hancock (1935) caged eight plants individually, infesting each with a usual average of 3-4 L. simonyi Reut, and with, never more than 10 individuals. per cage. He noted fewer nodes on infested plants, repressed branch growth, and tattered leaves. After caging individual bugs on individual bolls he concluded that the bugs caused shedding of these structures. Surfaces of damaged bolls had black-brown spots which coalesced to form sunken pits. Hancock mentioned further the possibility of boll shedding from lygus feeding on nearby leaves, although no data were given. Yield and quality measurements were not reported, Cassidy and Barber (1939) discussed the economic importance of Lygus spp, on cotton in Arizona. They reported that terminal buds were injured and young squares and bolls were blasted and shed. When bolls had developed beyond the age for shedding from lygus injury, the lint became stained or the bolls became mummified, opening prematurely with weak, short, impacted lint of little market value. From 1934 through 1937, these authors conducted annual boll surveys in upland cotton in different sections of Arizona, An average of 25% of all bolls examined over this four-year period were punctured. They concluded that

24 the probability of losses from blasting and shedding of leaf buds, squares, and young bolls was less serious than expected because of new compensatory fruiting structures produced after shedding. Smith (1942), discussing damage to cotton in California, reported that'l. hesperus caused a later crop, weak, fuzzy, discolored'lint, reduced oil content and poorer germination of seeds, in addition to the damage described above by other workers. Taylor (1946) studied L. simonyi damage to cotton in Africa. Daily comparisons were made between noncaged plants subjected to natural field infestations and those artificially infested with 25 nymphs at fortnightly intervals throughout the season to produce maximum damage. He constructed plant maps showing the fate of each fruiting point. At the end of the season, artificially infested plants were columnar rather than the usual conical shape, ragged in appearance, with fewer nodes on primary fruiting branches, shortened internodes, many abnormal secondary, tertiary, and axillary branches, and fewer bolls. Plants exposed to natural lygus infestations frequently shed young fruiting branches, replaced them with vegetative branches in the same axil, and occasionally produced two opposite vegetative branches at the cotyledonary nodes. Lygus bugs delayed flowering for about one jnonth.

25 The first studies of the influence of lygus bugs on cotton yields were reported from Africa by McKinlay in Protection of early-sown cotton with insecticides did not increase yields although the crop formed earlier. He concluded that the cotton plant had "remarkable powers of recovery from insect damage" and that only when the damage exceeded the point of recovery was protection necessary. "It is evident that the presence of insects feeding on the plant does hot always mean that such control would be necessary or profitable," he wrote. Goodman (1957) similarly concluded that the presence of insects plus a high rate of- square and boll damage cannot be regarded as prime evidence of economic damage to a crop. Coaker (1957) also reported that insecticidal control of Lygus spp. caused a retention of early fruiting bodies and an earlier crop but that shedding caused by lygus was not responsible for any serious yield reduction. The total amount of shedding of squares and young bolls was relatively constant. When shedding caused by lygus and bollworms was high, natural shedding was low, and when insect-caused shedding was low, natural shedding was high. Thus some factor other than pest attack governed the final crop retained by the plant. Compensation by cotton plants for early loss of fruiting bodies in an extended growing

26 8 season was further demonstrated in Africa by Ingram (1969), The effect of Lygus spp. on presquaring cotton plants was described by Wene and Sheets (1964). Lygus bugs killed 2-3 day-old cotton seedlings or caused deformed, late-squaring plants to develop when feeding occurred after cotyledon hardening. In other tests, squaring cotton plants were caged and infested heavily with L. hesperus to determine effects of injury to mid-season cotton. The ' infestation levels simulated conditions found when large numbers of lygus migrate to cotton from mature safflower. Infested plants showed a loss of squares, reduced boll set, increased height, and a reduction in final yields. Nymphs were considered about equal to adults in ability to damage cotton, Ripper and George (1965) describe in additional detail the damage to cotton by L. vosseleri. Attacks on young vegetative tissue, caused permanently deformed,. ragged leaves. Infested plants showed strong vegetative growth with main stem and vegetative branch apical buds unharmed. Wene, Carruth and Telford (1965) report that feeding punctures by L. hesperus and L. lineolaris caused warty growths on flower petals, brown spots on pistils and stamens, and unusually tall plants after prolonged feeding.

27 Lygus Feeding Strong and Landes (1965) reported that adult male L. hesperus consumed 5.7 yl in 24 hours when fed fresh or 97.6% of their body weight green bean juice through Para- film sealing the end of a f ood tube. Adult females with. maturing ovaries ingested'34.7 pi of bean juice or 169% of their body weight during the same time period. Ting (1963) reported that feeding and injury by L. lucorum (Meyer) in Chine was positively correlated with the total plant nitrogen content and that sap ph, sugar, and water content were of less importance. He suggested that plant nutrition might be used to regulate mirid populations. In California, L. hesperus was significantly more abundant in plots receiving the most frequent irrigations and the greatest rat^s of nitrogen application (Leigh, et al, 1970). King and Cook (1932) and McGregor (1927) suggested that lygus bugs inject some toxic substance into cotton plant tissue during feeding. Similar effects have been suggested for L, lineolarii? feeding on beans (Flemion, Ledbetter and Kelley 1954) and for L. hesperus feeding on guayule (Addicott and Romn<iy 1950), These latter authors reported that collapsed plant cells and obliterated structural details following lygus feeding indicated the presence of a toxic substa;ice Dale and Coaker (1958)

28 10 discussed the importance of the saliva injected into cotton by L. vosseleri, although they noted an increase in numbers of stem apex cells rather than collapsed cells following feeding, Flemion, Weed and Miller (1951) showed that L. lineolaris injected a secretion while feeding on bean pods. Strong and Kruitwagen (1968) reported that the toxic substance in lygus oral secretions was one or more powerful pectic glycosidases which release cell constituents for use as food. These authors found a polygalacturonase in the posterior lobe of the principal salivary gland of L. hesperus which was capable of degrading sodium polypectate in plants and seemed to account for the destructive capabilities of this pest. Strong (1968) considers square shedding to be of benefit to Lygus feeding on cotton. Shedding provides a self-regulating mechanism for producing more buds to replace those lost, thus the bug is assured of a continuing food supply. Shedding does not, as might appear, destroy a. limited natural supply of buds and cause increased competition for those remaining. Lygus Damage to Other Crops Lygus bugs attack other important crops. Similarities in damage exist between some of these crops and cotton.

29 11 Alfalfa, grown for hay or for seed, is attacked by L. hesperus, L. lineolaris, and L. elisus. Sorenson (1936), Carlson (1940), and Stitt (1944) have shown the effects of lygus feeding on developing seeds and other succulent plant parts on crop production. Lygus feeding causes a general lowering of yields with increased numbers of shriveled or brown, nonviable seeds. Hay crops show reduced vegetative growth, increased flower drop, and retarded new growth (Sorenson 1932, Shull, Rice and Cline 1934, MacLeod and Jeppson 1942, and Stitt 1948). Romney, York and Cassidy (1945) and Addicott and Romney (1950) reported that lygus injury to guayule seed caused collapsed embryos and poor germination. The guayule stem apex was also attacked causing adjacent young leaves to be severely shrunken, although feeding damage immediately behind the stem apex was less extensive. Hills (1941) reported that lygus feeding caused no significant reduction in weight or volume of sugar beet seed crops, although there was a marked reduction in germination. Carlson (1961) reported that L. hesperus was capable of causing yield reductions in table beet seed crops. In lettuce seed crops, lygus feeding did not cause reductions in yields or seed germination nor increases in the number of abnormal lettuce seedlings (Carlson 1959).

30 12 Safflower yields were not substantially reduced by relatively heavy infestations of L. hesperus (Carlson 1964, 1966), Young plants, were particularly capable of compensating for bud blasting after lygus feeding. Hill (1933) reported heavy attacks of L. lineolaris caused severe damage to celery including a blac.kening of leaves and leaf^stalks. L. lineolaris attacks the terminal growth of cucumber vines causing holes to' appear in the unfolding leaves (Harcourt 1953). Petherbridge and Thorpe (1928) reported similar damage from L. pabulinus feeding on young currant leaves. Lygus damage has been reported on sweet peppers, lima beans, blackeye beans, and tomatoes. Like cotton, the tomato plant is indeterminate in its growth habit. It is therefore of interest that feeding by L. lineolaris causes an increase in tomato flower production and an increase in fruit set, although the size and yield of fruit are reduced (Davis, McEwen and Robinson 1963), L. hesperus and L. lineolaris can cause the shedding of lima bean blossoms and of pods up to 2 inches in length. The seeds may be shriveled, with numerous necrotic pits (Shull 1933, Baker, Snyder and Holland 1946, and Elmore 1955), L. lineolaris causes increased bud and blossom drop of sweet peppers according to Huber and Burbutis (1967). Egg deposition in terminals, buds, blossoms and small-pod stems

31 of pepper caused die-back and abscission. Blackeye bean seeds attacked by L. hesperus and L. elisus become distorted and shriveled, with reddish-brown necrotic spots at feeding sites (Middlekauf and Stevenson 1952).

32 MATERIALS AND METHODS This work was conducted during 1969 at the Campbell Avenue Farm of the Agricultural Experiment Station of The University of Arizona, 4.8 km north of the Tucson campus. The cotton variety was Deltapine 16, planted on April 24, 1969 at a row spacing of 91 cm in two 8-row irrigation borders 122 m' long. The soil was a sandy loam consisting of 72.2% sand, 25,8% silt, and 2,0% clay (Slosser 1968), It was fertilized prior to planting with cow manure at the rate of approximately 20 tons per acre. Type of Experiment and Design To provide the maximum amount of information for the time and resources available, the present study was designed on factorial principles (LeClerg, Leonard and Clark 1962, and Ostle 1963). The two main.factors"under consideration were the time of lygus infestation and the lygus feeding stages present. The time-of-infestation factor was divided into four levels or treatments "entire" (June 12 to August 16), "early" (June 12 to July 3), "mid". (July 4 to July 25), and "late" (July 26 to August 16) infestation periods. The feeding-stage factor was divided into two levels-^-late-instar nymph and adult male L. 14

33 15 hesperus. Hence, this was a 4 x 2 factorial experiment involving four periods of time and two lygus feeding stages. Summaries of the treatments and combinations are given in Tables 1 and 2, The entire infestation period includes the approximate period of production of cotton squares capable of developing into mature bolls by the end of the season and the period of potential square injury from lygus infestation. In this study, the entire period extended from the date of first squaring until mid August. The early infestation period was the 22-day span from first square to first flower, and the mid and late infestations refer to successive 22-day periods from first flower until August 16, The addition of a third level of the ''B" factor no lygus present establishes the control for this experiment and theoretically makes this a 4 x 3 factorial experiment. Nymphs of both sexes and of either the fourth or fifth instar were used; adult males were selected over adult females to eliminate oviposition problems and possible unseen damage by new nymphs. The infestation level selected for this experiment was one bug per plant, which was the minimum possible level although it was approximately 10 times the usual field infestation level (G. D. Butler, Jr., Cotton Insects Laboratory, U.S. Dept. Agr., pers. comm., 1970). Any

34 Table 1. Identification of main factors and their levels. 16 Main Factor Code Levels Time of Infestation (A) a l. a 2 entire early June 12-Aug. 16 June 12-July 3 *3 mid July 4-July 25 a 4 late July 26-Aug. 16 Feeding Stage (B) b l b 2 b 3 no lygus present (control) late-instar nymph adult male Table 2. Treatments produced by combination of the various levels of the main factors. Main Factor A Level a l a 2 a 3 a 4 b l a l b l a 2 b i a 3 b l a 4 b l B b 2 a l b 2 a 2 b 2 a 3 b 2 a 4 b 2 b 3 a l b 3 a 2 b 3 a 3 b 3 a 4 b 3

35 17 given treatment combination had one nymph or adult male L, hesperus on one individually caged cotton plant for one of four periods of time. Morrill (1918) considered a field infestation of one lygus bug per plant to be more than sufficient to prevent all. boll setting and to cause the maximum damage possible. In this experiment, this level» of lygus bugs did not produce the drastic results that Morrill predicted. Each treatment combination was replicated three times for a total of 36 caged experimental units. The factorial arrangement had the advantage of "hidden replication" (Ostle 1963) in that 12 replications were actually obtained for each feeding stage arid six replications for each infestation period. The three replications were the minimum allowable for each treatment combination (A. B, Humphrey, Statistician, Ariz. Agr. Exp. Sta., Univ. of Ariz., pers. comm., 1969). The accuracy of this type experimentation could be increased with additional replications, but the required manpower and technical assistance were not available. In addition to the 36 caged observation plants, 12 additional noncaged plants were selectedeach located in the same row and 90 cm away from a caged control plant for similar observations to detect possible cage effects on plant growth and development.

36 18 A randomized complete block design, shown in Figure 1, was used for this factorial experiment. The blocks were located across the rows to, allow for possible fertilitygradients within the rows (LeClerg et al. 1962). The treatments were randomized within the blocks. Test plants were selected and caged at approximate 6 m intervals in rows 3 and 6 within each of the 8-row borders of irrigated cotton. Observation plants were isolated by thinning to provide a space of 61 cm on either side in.the same row to allow for placement of cages. Noncaged observation plants were similarly isolated. The cages were erected and treatments begun on June 12, 1963, a date which coincided with the first production of squares. Cage Construction Individual cages were cylinders of 16 x 18 mesh galvanized wire screening 105 cm high and 90 cm in diameter. Three pine stakes (5 x 5 x 130 cm) were equally spaced around the circumference of each, cage and attached with 1.25 cm staples (Duo-fast, Fastener Corp.). The first stake was attached at one end of the screening, the second at one-third of the screen's length, and the third at two-^ thirds of its length. The end of the remaining third of the screening was attached to the first stake by inserting it between the stake and a pine lattice strip (4.4 cm wide

37 19 BLOCK 111 c a 4 b 2 c l b 3 * a 2 b 2 a 3 b 3 C C 4 b 3 a 3 b 2 2 b 3 1 b 2. 3 b 2 a 2 b 3 1 b 3 C BLOCK II 1 b 2 c a 4 b 3 Q CT to 3 b 3 c C a 2 b 2 c 4 b 3 a 4 b 2 a 3 b 2 BLOCK 1 T b 3 a 1 b 2 C C C 3 b 3 a 2 b 2 a 2 b 3 ROW 3 ROW 6 ROW 3 1 ROW 6 SOUTH 8-ROW IRRIGATION NORTH BORDERS Fig. 1, Field layout of infested and noninfested control (C) cages in the lygus damage experiment.

38 20 and 100 can long) held tight with two 7.5 cm bolts and wing nuts. This permitted the cage to be opened and closed for daily examination of plants. After each observation, the top edge of this "door" was reattached to the cage top (a 90 cm diameter circle of wire screening) with 0.6 cm standard wire staples. The lower 30 'cm of each 130 cm stake was tapered to facilitate driving the stakes into the ground until the screen sides touched the surface. High winds accompanied frequent summer electrical storms but the cages were never blown over. Insect-proofing of the cages was accomplished by mounding soil around the base of each cage and by caulking small gaps at the junction of the cage top and "door" with wads of cotton lint. Source and Identification of Lygus hesperus All adults and nymphs used for infesting caged cotton plants were collected from alfalfa plants in the Tucson area. Bugs were either used immediately after capture or were maintained in the laboratory at 23 C in one-gallon glass jars until needed. The insects were regularly fed a diet of fresh green beans, Phaseolus vulgaris L, The age of the adults used for cage introduction was not determined nor was the time of last feeding before introduction known for either adults or late-instar nymphs,

39 21 Although L, hesperus is the most abundant species of Lygus on alfalfa in southern Arizona, another species, L. lineolaris, is usually present at low population levels (Clancy 1968), Both species were found in field collections during the summer of Adult male L. hesperus were readily identified by their greenish-yellow overall color, the brick-red diffuse spots toward the spex of the corium, and the pale scutellum with a dark mid-basal mark. Adult males of L. lineolaris are darker in appearance with darker membranes, no brick-red spots on the corium, and with a brown line on each side of the scutellum parallel to the margin (E\ G, Werner, Prof, of Entomology, Univ. of Ariz., pers, comm., 1969). Fourth and fifth instar nymphs of the two species were distinguished by the size of the dark spots on the notum. L. lineolaris has pronotal spots as large as the dark spots on the mesonotum while the spots on the L. hesperus mesonotum are smaller. L. hesperus has slightly larger wing pads (J. Phillip, Market and Product Representative, Chemagro Corp., pers. comm., 1969). The overall coloration of L, lineolaris nymphs was observed to be darker than the yellowish to green color of L, hesperus nymphs,

40 22 Collection of Data Growth and Fruiting Characteristics To observe growth ajid fruiting behavior, the test plants were examined daily from the date of appearance of the first square (June 12) until September 24, 1969, and weekly thereafter until November 26, At the same time, the lygus bug in each infested cage was located to insure that the proper feeding' stage was present and that it was in an apparently healthy condition. Dead bugs were removed and replaced. Plant height was measured weekly from June 12 to September 12 and was based on the length of the main stem from the cotyledonary node to the apical meristem, measured to the nearest inch. The number of squares, pinhead.size or larger, was determined and recorded daily. Yellowish squares which abscised easily when touched were counted as shed. All shed squares on the ground within each cage were counted and removed. Time did not permit a close examination of the interior of each shed square for lygus feeding damage, although it was noted whether or not they were "blasted". Blasted squares, as described by Strong (1968), are squares which, when attacked by lygus, turn brown, shrivel, and fall from the plant.

41 23 Flowers were counted daily from the date of first opening or anthesis (July 3) until September 24. Each flower was tagged to indicate the date of anthesis, using small white tags appropriately marked with a No. 2 softlead pencil and secured loosely around the peduncle of the square. The tags were retained on the plants until harvest for determination of flowering and boiling patterns. Bolls first began to open during the 7~day period ending August 22, The number of open bolls on the plants was counted and recorded every 7 days thereafter until harvest. Green boll counts were not made. After the final harvest, all observation plants were cut below the cotyledonary node and later examined in the laboratory to record the amount and type of branching (monopodial or sympodial, primary or secondary) f the number of nodes comprising the main stem f and the nature of any structural aberrations, Basic information and terminology on cotton plant morphology are reported by Dennis and Briggs (1969) f Mauney (1968), and Tharp (1965). Yield and Quality Measurements The first bolls were picked on October 4 when the bottom crop was mature, A second picking was made on November 26 after the maturation of the top crop. Seed cotton was harvested only from pickable open bolls, or

42 24 bolls with lint visible in at least one lock, using the method of Adkisson, Brazzel and Gaines (1963). Seed cotton samples picked on October 4 were weighed and ginned on October 10; those picked on November 26 were weighed and ginned on December 20, From'harvest until time of classing, the samples were stored in paper bags at laboratory temperature and humidity. Seed cotton and lint were weighed to the nearest \ 0,1 gm on a Welch triple beam balance. Each sample was "fleeced" 2-3 times, to remove larger trash, and ginned on an 8-saw gin in the Cotton Laboratory at The University of Arizona at Tucson. One hundred seeds were randomly selected from each sample and weighed to the nearest 0.01 gm on.a Torsion balance to give a seed index measurement. Ginned samples were graded by the U.S. Department of Agriculture Cotton Classing Office in Phoenix, Arizona, on October 14 for the first picking, and on January 2, 1970, for the second picking. This office provided quality measurements of grade, staple length, and micronaire. Grade is a qualitative measure based on the color of the lint, presence of leaf and other trash, and degree of smoothness or roughness of the lint after ginning. Staple length refers to the normal length of typical fibers at 20 C and 65% R,H, Micronaire is an expression of the fineness and maturity of the lint. Fine, immature lint

43 has lower micronaire values than coarse, mature lint. Prom these three official cotton classing standards, the monetary value of the lint was computed using the cotton loan quality values.and location differentials as published by Merrill Lync.h, Pierce, Penner and Smith, Inc.. «Lygus Feeding Experiment h separate experiment was carried out in the same field plots during mid and late August, 1969, to observe the feeding of L, hesperus and the fate of injured plant structures. Insects caged with squares and leaves were allowed to feed and were then removed. Daily examinations were subsequently made to observe possible abcission of fruiting structures. Insects were confined in cylindrical, clear plastic cages (3x5 cm) enclosed at one end with saran screening and at the other end with a foam rubber plug fitted around a branch internode. Cages enclosed a square and its corresponding leaf and were located at each of four positions on the fruiting branch, i.e., at the first through the fourth nodes of the first axillary axis. One position on each of two branches on one plant was caged. One cage served as a control and the other as the treatment. Six replications were used for testing each of the three feeding stages: late^instar nymph, adult male, and adult female. The 25

44 treatment cages were located on the lower branches in three replications and on the upper branches in the remaining three replications. The squares on the lower branches were slightly larger than those on the upper branches, and this alternating arrangement permitted detection of plant re-.. sponses differing because of square size* Adjacent leaves» were included in the test cages because of their structural relation to the squares and the possible detrimental effect on squares from nearby leaf feeding (King and Cook 1932, Hancock 1935), Thus each treatment included one lygus bug in one cage containing a square and its leaf, located at one of four positions on a fruiting branch, replicated six times with three replications on lower branches and three on upper branches. Each lygus bug was introduced into its given cage and observed from the time mouth parts were inserted into the plant tissue until they were withdrawn. Feeding times of less than one minute were arbitrarily termed "probes". and, therefore, only times greater than one minute were recorded. Each feeding location was recorded and bugs were promptly removed after feeding. Individual lygus bugs were used only once. All bugs used in these tests t had been maintained in the laboratory on"green beans for at least 2 days. Following feeding, the cages were 26

45 27 examined daily to determine the fate of the plant structures within. Adult males were tested on August 15-16, adult females on August 20-21, and late-instar nymphs on August 31. Daily plant observations were continued until Septem- ber 22. \ Effect of Cages According to Fye, Bonham and Leggett (1969) and Hand and Keaster (1967), cages may modify the surrounding environment to such a degree that the reliability of data may be affected.. Smith (1931) reported that the mean temperature inside a large, galvanized wire cage placed over an alfalfa plant was only 0.83 C higher than outside. Fye et al. (1969) reported a slightly lower temperature inside than outside a wooden-frame cage (50 x 50 x 64 cm) covered with 18 x 14 mesh screening and containing a potted cotton plant. They attributed this decrease to a shading of the cage by the screen and frames and to the respiratory activities of the plant. Measurements of temperatures inside and outside a cage used in this experiment (Cage a^3, Block II) were - made with recording thermometers (Marshalltown Mfg. Inc., Model 1000) during two 7-day periods extending from August 7 to 14 and from August 17 to 24, The sensing unit

46 28 from each thermometer was directed into a shaded area near the main stem of the plant approximately 75 cm above the ground. The mean maximum temperature outside the cage during these two 7-day periods was 41 C while the mean high temperature inside the cage was only 37.5 C. This difference of 3.5 C was statistically significant at the 1% level. The mean minimum temperature during the recording period was 20,3 C outside the cage and 20.6 C inside. These minimum temperatures were not statistically different. It is concluded that the lower maximum temperature within the cage is a direct result of shading from the screen wire as suggested by Fye et al. (1969). This is further confirmed by the similar inside and outside low temperature means which occurred in darkness or immediately before sunrise when shading was not a factor. Relative humidity, evaporation, solar radiation, and air movement within and outside the cages were not determined. Such measurements in similar cages have been reported by Smith (1931) and Hand and Keaster (1967). Relative humidity may be somewhat lower inside caged enclosures but the slight differences usually observed have not been significant. The latter authors report that 84% of the outside precipitation was measured inside a walk-in saran screen cage. Water evaporation was.20% less, solar

47 29 radiation was 19% less, and the average wind speed was 51.5% lower than outside the cage. Although it seems probable that environmental modifications occurred within the cages used in this study, their significance could not be ascertained. Caged and noncaged control plants had nearly identical growth and fruiting patterns throughout this experiment and deviations from these similar patterns could be related to natural insect infestations on the noncaged plants. Ewing and McGarr (1933) reported that 16-mesh galvanized screen cages were the most suitable for this type of work because of the normal plant growth and fruiting patterns which occurred, Climatological Data The climatological data used in this study were recorded at the Campbell Avenue Farm of the Agricultural Experiment Station of The University of Arizona and published by the Environmental Data Service of the U.S. Department of Commerce (1969). The instruments were located approximately 0.4 km northwest of the experimental plots at 32 17' latitude, ' longitude, and 0.7 km elevation. The climatograph shown in Appendix A includes daily minimum and maximum temperatures and daily rainfall, plotted from the time of planting until final harvest.

48 This climatograph also includes irrigation dates and other major events in the life of the crop. Average monthly temperatures and precipitation values did not deviate «during 1969 from previously recorded values for this location. 30 Statistical Procedures The analysis of variance (ANOVA) was used to test for significance of the simple effects of the main factors and for interactions between these factors. Growth measurements at given dates for plant height, number of squares, flowers or open bolls, and for yield characteristics were treated in this manner. Appendix B contains the ANOVA tables used for each analysis including component's, degrees of freedom, and working definitions of sums of squares. The upper table, called the treatments ANOVA, partitions the total sums of squares of deviation of lygus treatments into A (time of infestation), B (feeding stage present), and AB (interaction between A and B) variables plus random error. The lower table, called the treatments plus control ANOVA, partitions the total sums of squares into control vs. treatments and within control variables plus the A, B, AB variables from the treatments ANOVA, The total error in the experiment, as shown in the lower table was partitioned into error within treatments and error within controls. These error terms were always

49 31 compared to insure that the error was similar in both treatments and control. A significant P test for a given variable in the ANOVA table showed that there was sufficient evidence to indicate a difference in the overall means of that variable,.when F tests were significant for A, B, or AB factors, *overall means or means for treatment combinations were separated by use of Duncan's multiple range test (Steele and Torrie 1960). If comparisons were made between means calculated from unequal replications, i.e., control mean vs.. overall "A" treatment means (12 vs. 6) or control mean vs. means of treatment combinations (12 vs. 3), the modified Duncan's multiple range test (Kramer 1956) was used. In this case, the significant studentized ranges were obtained by multiplying the tabular value by the square root of the error mean square to give intermediate ranges. These values were then multiplied by \f% (1/r^ + 1/rj)', where r^ = replications of treatments, and rj = replications of controls. Linear regression and correlation analysis was utilized to analyze continuous data (patterns of main stem elongation, squaring, flowering, and boiling) over a period of several weeks or months to determine if the data could be approximated by a straight' line and allow statistical comparisons between lines. An Olivetti- Underwood Programma 101 desk-top computer was used to

50 32 carry out these calculations, using a linear regression and correlation analysis program. If straight lines approximated the data, F tests for the homogeneity of regression coefficients were carried out with the same equipment. Cumulative percentage curves were used to depict» progress of flowering and boiling. To test whether these cumulative distributions differed statistically, the nonparametric Kolomogorov-Smirnov 2-sample test, as outlined by Siegel (1956), was utilized. In this procedure, a given cumulative distribution from a particular treatment was compared against the cumulative distribution of the caged control. If at the point of maximum deviation (D) the absolute value deviated beyond a calculated critical value, the samples were drawn from different populations. Critical values of D were calculated with the expression, k + n 2 /n^n2', where n = the number of flowers or bolls accumulated in the control (n^ and treatment (n2> The critical D values calculated for the cumulative percentage curves analyzed are listed in Appendix E. The 5% level of significance was accepted as standard for all statistical tests. When tests were significant at the 1% level, this was recorded. When significance was found only at the 10% level, the results were discussed but excluded from tables or graphs.

51 r RESULTS Plant Heights and Structure Plant growth observations, as measured by height. of the main stem throughout the season, are summarized in Figures 2, 3, and 4.' Heights of caged and noncaged control plants are given in Figure 2. Growth curves for the caged control plants compared with plants exposed to hesperus are shown in Figures 3 and 4, Growth was most rapid between June 12 and July 24. During this early period, weekly mean increases in height ranged from 3,6 to 17,8 cm. Weekly mean height increases later in the season were usually 2.5 cm or less (Table 3). All graphs indicate that final heights of nymph-infested plants was somewhat greater than adult-infested plants or caged control plants. Linear regression and correlation analysis were carried out on these plant growth curves, but they showed that some curves could not be approximated with straight lines. It was therefore not possible to test for the homogeneity of regression coefficients. Since these growth curves comprise two distinct sections, two regression lines could be computed for each section. This might show high degrees of correlation although suitable statistical methods 33

52 34 E v O) '«X c o o V S caged noncaged 18-1 i i i i i i i i i i i i i E June July Aug. Sept. Pig. 2, Weekly mean heights of noninfested caged cotton plants and nearby noncaged plants.

53 Infestation Period entire Infestation Period early 102T^c3 I * nymph -adult & caged control June July Aug. Sept. i i i i i i i i i i i i i i June July Aug. Sept. Fig-. 3. Weekly mean heights (cm) of cotton plants exposed to one nymphal or adult male L. hesperus during the (A) entire and (B) early infestation periods. u> cn

54 102- Infestation Period mid k i * i ^ } j'. 1 1 r - >' B Infestation Period late 89- u 76 _c o) 64 «= 51- o «= 38- o 4> nymph adult «? caged control 1 i i i r-i i i i i i i i i June July Aug. Sept June July Aug. Sept. Fig, 4, Weekly mean heights (cm) of cotton plants exposed to one nymphal or adult male L, hesperus during the (A) mid and (B) late infestation periods. lo

55 Table 3. Weekly mean increase in plant height (cm) for noninfested control plants and plants infested with one nymphal or adult male L. hesperus during four infestation periods. 3 Date Control Nymph Infestation Adult <? Infestation Caged Noncaged Entire Early Mid Late Entire Early Mid Late July Aug. Sept. 19 7, , ,6 3, , , , , , , , , ' , , ,3 1, , , a Vertical lines indicate approximate duration of infestations.

56 38 are not yet available, for segmenting such curves at the optimal points (J, Gebert, Statistician, Ariz. Agr. Exp. Sta., pers. comm., 1970). Curvilinear analysis was not considered suitable because of the small number of replications per treatment (Gebert, pers. comm., 1970). Final mean plant heights for the various treatments and the results of the ANOVA are summarized in Table 4, including the final heights for the treatment combinations, the overall means for the four levels of the time-ofinfestation factor and for two levels of the feeding-stage factor, and for the caged control mean. Plant heights did not differ significantly between treatment periods although there were significant differences between plants exposed to adult or nymphal feeding and the control plants. Main stem growth was always greater in plants infested with nymphs. Since there was no significant interaction between the time-of-infestation and feeding-stage factors, the effect of the feeding stage on plant height is probably independent of infestation period. Mean height of noncaged control plants (76.2 cm) was not included in the ANOVA but was compared instead with caged control plants using Student's "t" test. This test showed that the final heights did not differ significantly, and therefore, the presence of the cages >

57 Table 4, Mean plant height (cm) on Sept. 18, 1969, following infestation by one nymphal or adult male L. hesperus during four infestation periods. 39 Infestation Period Feeding Stage Mean per Nymph Adult Period Caged Control Mean Entire CO CO * vo Early 96,5 CO CO «H 92.2 Mid vo vo CO Late 97, Mean per Stage: 96, 3x 81. 8y 89, y a These means were compared with the caged control mean by Duncan's multiple range test? they do not differ significantly at the 5% level. ^These means were compared with the control mean; those followed by the same letter do not differ significantly at the 5% level. c Grand treatment mean.

58 40 apparently did not have an important affect on main stem elongation, Measurements of the gross structure of the observation plants at the end of the growing season are shown in Table 5, The mean number, of main stem nodes ranged from. 24,3 (mid period infestation of adults) to 28.0 (early period infestation of nymphs). Significant differences existed between nymph-and adult-infested plants but only at the 10% level. The numbers of primary fruiting branches did not differ between treatments although a significantly higher number of primary vegetative branches were present on plants infested with nymphs during the early period of infestation. In this latter case, the ANOVA showed differences among adult- and nymph-infested plants and that there was a significant interaction between the. time-ofinfestation and feeding-stage factors. Any simple treatment effect is thus dependent upon the level of the other factor or, as was indicated by Duncan's multiple range test, the simple effect of the nymphs is dependent on the entire infestation period. Vegetative branches may also give rise to secondary fruiting branches. Although the mean number of secondary fruiting branches ranged from 32,7 (late"period infestation of adults) to 52,0 (mid period infestation of nymphs), as shown in Table 5, significant differences were not

59 Table 5. Mean number of main stem nodes and vegetative and fruiting branches on noninfested caged cotton plants and on plants exposed to one nymphal or adult male L. hesperus during four infestation periods. Feeding Stage Period of Infestation Main Stem Nodes Primary Vegetative 3 Number of Branches Primary Secondary Fruiting Fruiting Total Fruiting Nymph entire a early abc " 62.7 mid abed * late abed Adult 6 1 entire d early ab mid abed late cd Caged Control' bed a Means followed by the same letter do not differ significantly at the 5% level.

60 42 detected. Even though nymph-infested plants had significantly more vegetative branches during the entire period, they did not have a correspondingly higher number of secondary fruiting branches. The number of primary fruiting branches and the total number of both types of fruiting branches did not differ significantly between infested and noninfested plants. Patterns of Square Production To determine the exact number of squares produced, it would have been necessary to mark all new squares each day. Since this was not possible within the available time, the patterns of square production were determined indirectly by counting the numbers of squares pin-head size or larger present on the plants each day throughout the i season. The squaring patterns determined in this manner are shown in Figures 5 to 9. Figure 5 compares the squaring curves for the noninfested caged plants and the noncaged control plants. Two general peaks in the squaring pattern are obvious, one on July 13 and another in mid-september, The valley between the peaks represents a "cut-out", or period of fruiting adjustment. The cut-out period is greatly pronounced in this experiment because one July irrigation was missed. This caused the plants to become water-stressed and apparently caused additional square shedding beyond the

61 S5 Z < SO VI UJ te <" Z> a i/> noncogcd control caged control JUNE JULY AUGUST SEPTEMBER Fig. 5. Squaring patterns of caged and noncaged control plants.

62 44 INFESTATION P E RIOO Entlra '.VV..'I.''.: 3 ifviyftw V ''<, " l '.7 VW *i 1 L : V VHK.Si nymph adult cf caged control JUNE JULY aucusr SEPTEMBER 6. Squaring patterns of plants exposed to one.nymphal or adult male L. hesperus during the entire infestation period.