EVALUATION OF CORN INBRED LINES FOR RESISTANCE TO STALK BORER, PAPAJPEMA NEBRIS,,2

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1 EVALUATION OF CORN INBRED LINES FOR RESISTANCE TO STALK BORER, PAPAJPEMA NEBRIS,,2 Robert K. D. Peterson, Scott H. Hutchins, and Paula M. Lasack Department of Entomology Iowa Agriculture and Home Economics Experiment Station Iowa State University Ames, IA Abstract: Studies were conducted in 1985 and 1986 to evaluate the status of European corn borer resistant corn lines on stalk borer, Papaipema nebris (Gue1ll3e). Three inbred corn lines were evaluated in greenhouse tests in 1985 in a completely random design with 10 replications per inbred. No statistical differences were observed among lines B73, B75, or B86 when plants were rated on a 0-4 damage scale. In 1986, field studies were conducted utilizing a randomized complete block design with five inbred lines [B73, B85, 852, 886, BS9(CB)C5), fouf replications, and ten subsamples per plot. Results suggest that BS9(CB)C5 experienced the least injury from stalk borer infestations, with the proportion of severely damaged plants significantly reduced (P < 0.05). Based on the results from these studies, breeding and further testing of com genotypes for management of stalk borer is recommended_ Key Words: Stalk borer, PapClipema nebns, corn, Zea mays, DIMBOA, host resistance. J. Agric. Entomol. 4(1): (January 1987) The stalk borer, Papaipema nebris (Guenee), is a native North American insect that has, in recent years, become increasingly important as a pest of seedling corn, Zea mays (L.). Increased weed populations associated with conservation and no-till cropping systems have resulted in an increase in stalk borer damage. This increase is the result of an ovipositional preference for perennial grasses and weeds (Stinner et a ). The pest is univoltine in Iowa with larvae normally undergoing seven to nine instars. Upon eelosion in the spring, larvae bore into suitable grass weed species, feeding in the stem of the plant until the girth becomes too small to accommodate additional growth of the larva (Decker 1931). At this point, larvae move to large-stemmed plants and continue to tunnel. Frequently, in agronomic situations, third- and fourth-instal' larvae infest nearby corn_ Damage to com is evident as 'shot-hole' leaf feeding, and, subsequently, whorl death (Lowry 1927; Decker 1931). If the corn plant is attacked late in its development, it will usually escape severe damage and show little or no sign of attack (Decker 1931). Inasmuch as predicting tile time of movement into corn is difficult, conventional insecticides have proven somewhat ineffective as a control method for stalk borei' larvae. Therefore, other methods of control warrant investigation. Host resistance has been demonstrated with another tunneling pest of corn, the European corn borer (ECBj, Ostrinia nubilalis (Hubner). K1un et al (1967) repol~ed that the biochemical basis for resistance to leaf feeding by first generation ECB was 2,4 dihydroxy-7-methoxy-l,4 benzox8zin-3-one (DITvIBOA). Several inbred lines have since been developed that are resistant to first, second (sheath-collar feeding resistance), or both generations of EeB in Iowa (Guthrie and Dicke 1972; Guthrie LEPIDOPTERA: Noctuidne. 2 Accepted for publication 27 March

2 PETERSON et 81.: Stalk Borer Resistance in Corn 67 et ). These inbred lines, however, have not been tested for resistance against stalk borer. Hence, the objective of this study was to evaluate ECB-resistant inbred corn lines for resistance to stalk borer feeding. In addition, the consequences of using genotypes of corn resistant to stalk borer is discussed. MATERIALS AND METHODS Experiments were conducted in 1985 and 1986 to evaluate ECB-resistant inbred lines for stalk borer resistance under greenhouse and field conditions Greenhouse Experiment Three inbred corn lines, with 10 replications (plants) each, were planted individually in pots (11.35 liter capacity) on 12 July and allowed to grow to the 3-4 leaf stage. On 26 July, each plant was infested by carefully transferring one larva from its rearing dish directly into the whorl of the plant with a camel-hair brush. Larvae used in the experiment were reared from eggs obtained from gravid moths the previous season. Third and fourth-instal' larvae were used because field grown corn is typically attacked by larvae of this size. The three inbred lines tested, with reference to ECB status, were: 873 (susceptible to leaf feeding by first-generation ECB and sheath-collar feeding by second-generation EeB), 875 (resistant to first generation EeB only), B86 (resistant to first and second generations of EeB). Injury to infested plants was assessed at 4, 6, and 9 d postinfestation. Plants were rated as having: 0, no leaf feeding; 1, leaf feeding only on old leaf tips; 2, light leaf feeding in whorl and (01') stem tunneling; 3. heavy leaf feeding in the whorl; and, 4, dead-heart. Experimental units were arranged in a completely random design. Data were subjected to analysis of variance, with means separated (P < 0.05) by the Student-Newman-Keuls range test (Newman 1939). J986 Field rest To expand the scope of the evaluations and incorporate field conditions into the experiment, five inbred corn lines were planted neal' Ames, LA, on 9 June. Plots /7.6-m by 4 rows (76.2-cm wide)j were arranged in a randomized complete block design, with each valiety replicated four times. To account for plant to plant variation, 10 plants within each plot were evaluated for resistance. Inbred lines evaluated in the expanded field tests were: B73, B85 (resistant to first generation ECB only), B52 (resistant to second-generation ECB only), B86, BS9(CB}C5 (resistant to first- and second-generation of ECB). Each plant was infested as in 1985 at the 4-5 leaf stage (8 July) in the whorl with a single fourth- or fifth-instar stalk borer larva. Injury to the infested plants was assessed as in 1985 but at 3, 8, and 15 d postinfestation. In addition to evaluating raw damage ratings, data were transformed to proportion of plants expressing any feeding injury (i.e., no. plants rated 2:. 1.0/no. plants infested) and proportion of severe feeding injury (i.e., no. plants rated 2:. 3.0/no. plants infested). This procedure was done to account for the fact that severely damaged plants have been shown to exhibit significant yield losses while damage by light leaf feeding is minimal (Bailey and Pedigo 1986; Levine et al. 1984). Hence, severely damaged plants represent future yield losses more accurately than raw ratings. Data were evaluated by analysis of variance (nested design for raw ratings) with means subjected to the Student-Newrnan-Keuls range test (P < 0.05).

3 68 J. Agric. Entomol. Vol. 4, No. 1 (1987) RESULTS AND DISCUSSION Results from the 1985 greenhouse evaluation of corn inbred lines did not indicate resistance to common stalk borer (Fig. 1). Although there was a numerical difference between the lines, there was enough plant to plant variation to obscure statistical significance. In addition, varieties often ObSCIVCd to be high in DIMBOAbased resistance to ECB under field conditions have often failed to perform under greenhouse conditions (Guthrie et al. 1986) Damage rating value 875 IIllIllllllllll 4 a a ~ 2 o 4 6 Days postlnfestatlon Fig. 1. Mean greenhouse damage ratings of com inbred lines at three postinfestation intclvals. Bars labelled by the same letter within rating dates are not significantly difrerent (df ~ 2, 27; P < 0.05) based on the Student Newman-Keuls range test. Ames, lao Results from the field experiment with five inbred lines demonstrated statistical differences at each postinfestation date when raw damage ratings were compared (Table 1). Three days after infestation, inbred line B85, which is resistant to first generation EeB, showed resistance to early feeding by stalk borer. Eight days after infestation, only BS9(CB)C5 demonstrated resistance to stalk borer feeding. At the final rating date, the rankings remained the same, with BS9(CB)C5 injured significantly less than the other inbred lines. The data suggest that factors affecting resistance to both first and second generations of Eea arc necessary to achieve stalk borer suppression. Moreover, because BS9(CB)C5 is more resistant than B86, the mode of resistance to stalk borer probably is different between these two lines. Guthrie (1981) noted that 95% of resistance-induced mortality fol' ECB occmred during the 5 d following egg hatch on corn. Since stalk borer larvae

4 PETERSON et al.: Stalk Borer Resistance in Corn 69 Table 1. Mean lield damage ratings of corn inbred lines at three postinfestation dates. Ames, la Days postinfestation Inbred com line U3a" 1.65a 1.53a 885 a.68b 1.78a 1.83a 852 U3a 2.03a l.76a 886 l.03ab 2.03a 1.93a 8S9(C8lC5 0.78ab 1.08b l.oob F-value Means followed by the same leiter within columns {Ire not significnnlly different (df = 4. 12; P < 0.05) based on the Student-Newman-Keuls range test. initialy develop on weed hosts, control from ECB-resistant corn lines may be less dramatic. "''hen data were transformed to represent proportion of plants expressing any leaf feeding, the differences were less dramatic (Table 2). Differences between lines did not become obvious until 8 d after infestation, when BS9(CB)C5 had less leaf feeding that the other lines. This response suggests that stalk borer larvae begin to feed on all inbred lines, but: may not continue to feed on BS9(CB)C5. On lhe linal sample date, BS9(CB)C5 remained relatively resistant to leaf fceding, but B85 and B52 also demonstrated some level of resistance to overall leaf feeding. Table 2. Mean proportions of corn inbred Hnes expressing any feeding injury in the lield at three postinfestation dates. Ames, IA Days postinfestation l.nbl'ed corn line s O.BOab 0.90a 885 0,48a 0.83ab O.BOab a O.90a O.77ab 886 O.73a O.90a 0.90a 8S9(C8)C5 0.53a 0.70b 0.63b "'-value 2, l\-leans followed by the same letter within columns are not significantly different (df = -I, 12; P < 0.05) based on lhe Sludcnl-Newmon-Keuls range lest. Evaluation of the pl'opol'tion of severely damaged plants (Table 3) reveals that BS9(CB)C5, once again, expressed superior qualities at the final two rating dates. Based on these evaluations, BS9(CB)C5 may be useful in breeding tests to incorporate complete or partial resistance to seedling corn subject to stalk borer attack. From a management standpoint. the potential use of host resistance to stalk borer could mean reduced insecticide inputs to corn grown in minimum and no Ullage cropping systems. Moreover, in terrace situations where generally only the first four to eight ro\'io's are subject to attack (Levine et a ), resistant varieties may provide a management alternative. For example, rather than attempting to manage stalk borer larvae with insecticides as they move from weeds to corn,

5 70 J. Agric. Entomol. Vol. 4, No. 1 (1987) Table 3. Mean proportions of com inbred lines expressing severe feeding injury in the field at three postinfestation dates. Ames, IA Days postinfestation Inbred corn line B a' hc B B a b B b BS9(CBjC b 0.25c F-value Means followed by the same leller within columns are not significantly different (df "" 4, 12; P < 0.05) bosed on the Student NewmOIl Keuls range test.. resistant varieties may be used in border rows to limit damage. This system would maintain the integrity of the cropping operation (i.e., com is still planted and tilled as before) but eliminate the need for an application of insecticides. In these experiments at least one inbred line of corn, BS(CB)C5, shows potential for reducing damage by stalk borer. Based on this finding, we recommend further investigation and bl'eeding trials to evaluate the wide-scale potential for using resistant varieties as a management strategy. ACKNOWLEDGMENTS We thank W. D. Guthrie, USDA-ARS Corn Insect Research Unit~ Ankeny, la, for providing the com gennplasm for these tests and for providing valuable suggestions regarding the preparation of this manuscript. This is Journal Paper NO. J-J2541 of the Iowa Agriculiure and Home Economics Experiment Station, Ames, la, Project No REFERENCES CITED Bailey. W. C., and L. P_ Pedigo Damage and yield loss induced by stalk borer (Lepidoptera: Noctuidae) in field corn. J. Econ. Entomo!. 79: Decker, G. C The biology of the stalk borer, Papaipema nebn's (Gn.). Iowa Agric. Exp. Sln. Res. Bull. 143: Guthrie, W. D., and F. F. Dicke Resistance of inbred lines of dent corn 10 leaf feeding by 1st-brood European corn borers. Iowa State J. Sci. 46: Guthrie, \1.,,7. D Maize whorl stage resistance to the first four instars of the European corn borer larvae (Lepidoptera: Pyralidae). J. I<anstls Entomo!. Soc. 54: Guthrie, Vol. D., W. A. Russell, and C. W. Jennings Resistance of maize to secondbrood European corn borers. Proc. Annu. Corn Soybean Res. ConL 76; 8]8-820_ Guthrie, W. D., R. L. Wilson, J. R. Coats, J. C. Robbins, C. T. Tseng, J. L. Jarvis, and W. A. Russell European corn borer (Lepidoptera: Pyralidae) leaf-feeding resistance and OlMBOA content in inbred lines of dent maize grown under field versus greenhouse conditions. J. Econ. Entomol. 79: KllIn, J. A., C. L. Tipton, and J. A. Brindley ,4 dihydroxy-7 methoxy-1,4 benzoxazin-3 one (DIMBOA), an active agent in the resistance of maize to the European corn borer. J. Econ. Entomo!. 60: 1529-J533. Levine, E., S. L. Clement, and D. A. McCarlney Effects of seedling injury by the stalk borer (Lepidoptera: Noctuidae) on regrowth and yield of corn. J. Econ. Enlomol. 77:

6 PETERSON et a1.: Stalk Borer Resistance in Corn 71 Lowry, P. R The stalk borer. New Hampshire Agric. Exp. Stn. Tech. Bull pp. Newman, D The distribution of range in samples from a nonna) population, expressed in terms of an independent estimate of standard deviations. Biometrika 31: SUnner, B. R., D. A. McCartney, and W. L. Rubink Some observations on ecology of the stalk borer (Papaiperna rwbn's [Gn.l: Noctuidue) in no-tillage corn agroecosystems. J. Georgia Entomol. Soc. 19: