Indian [n<;titutc of Horticultural Research, Hessuraghattu, Bangalorc. India

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1 Entomon 1989 Vol. 14 No.3 & 4 pp. 319 to 324 ECOLOGICAL STUDIES ON CITRUS PSYLLA, DIAPHORINA CITRI KUWAYAMA (HEMIPTERA: PSYLLIDAE) WITI-I SPECIAL REFERENCE TO ITS SPATIAL DISTRIBUTION AND SAMPLING PLAN B. DHARAJO'lHl, ABRAHAM VERGHESE & P. L. TANDON Indian [n<;titutc of Horticultural Research, Hessuraghattu, Bangalorc. India (Rect?il'ed 30 Dcccmber 1988) Basic ecological studies on spatial distribution nod sampling plan were conducted to understand the population dynamics of the citrus psylla, Diapliorillll citri Kuwayama. New shoots of citrus were salnpled. The eggs and nymphs followed contagious distribution, where.as the adult distribution was random to aggregated. The data fitted a negative binomial model, with a probabijit)' range of 0.03 to 0.99, add 0.19 to 0.98 for eggs and nymphs, respectively. There was no significant differences in the mean population density among the four directions. Sample sizes recommended for D. did are 40, 38, arid 19 shoots/tree for eggs, nymphs and adults r~pecti"cl)'. The relevance of these findings to the manngement of D. dtri is discussed. (Key wol'd~: citrus. psylla. Dwpho/'ltw citrt, spatial distribution, sampling) INTRODUCTION NIA TERJALS AN D METHODS The citrus psylla, Diaphorilla curl Kuwayama is one of the key pests of citrus in India. It attacks almost all the commercially cultivated citrus species. Apart from the feeding damage, it acts as a vector of greening disease of citrus which is the prime cause of citrus decline in India (BINDRA, 1966, 1969: BHUTANI, 1979: CAPOOR et a!., 1967). Besides India, it is widely distributed throughout tropical and Sli b~tropicaj Asia and the Far East and has been recorded from Pakistan.. Sri Lanka, Burma, Malaysia, Indonesia, Southern China, Ivlacao, Taiwan and the Philippines (BINDRA, 1970). The present basic ecological studies on spatial distribution, and sampling plan were conducted to understand the population dynamics of D. citri for Ats effect.ive managemem. Contribution No. 296/88 of rndian Institute of Horti. cultural Research. Bangalore. The present studies were conducted at the Experimental Research Station of the Indian Institute of Horticultural Research, Hessaraghatta, Bangalore on ten trees of acid lime selected at random, having uniform size and age. These trees were kept free of insecticidal sprays during the study (July-August 1989). From each t.ree ten new shoots (4 to 5 cm) were sampled at random from each cardinal direction viz., East, West, North and South making a total sample of 40 shoots per tree. The shoots were cut and collectcd in glass tubes and brought to laboratory for population estimation. The egg and nymph populations were counted by observing the shoots under a binocular dissection microw scope. However, adult population was counted in the field. The data were subjected to the analysis of dispersion indiccs. variancemmean ratio, mcan crowding, LLOYDS (1967) index of

2 320 B. DHARAJOTHI ET AL. patchiness, Iwao's patchiness regression (IwAo, 1968) and the exponent-k. After finding the distribution trend from dispersion indices, the data were fitted to a negative binomial distribution for within tree and overal1 population. The fit to the negative binomial was tested against chi-square and the probability of fit was computed in all cases. The mean clump size (A) was calculated to identify the cause of aggregation from the following formula of ARBOUS & KERRleR'S (1951). - x A =-- V 2k where x = mean, and v =-: a function with a X2 fdistribution. with 2k degrees of freedom at the 0.5 probability level. Analysis of variance (ANOY A) was cal.. culated for the data on population from four directions of a tree to find if the mean population density of D. citri differed significantly within the sections of the canopy. The correlations of the pest population in these sections with the total population in the tree were also worked out. To calculate the optimum sample number/ tree for field estimation of psylla population the formula of COCHRAN (1977) was used. with margins of errors at 10% and 20% Cd) with reference to mean values at 5 ~Yo confi dential limits (t-value). RESU LTS AND Spatial distribution of eggs: DISCUSSION The different parameters, mean density (x), variance (82), variance mean. ratio (82/ ;), index of mean crowding (x*), Lloyds index of patchiness, (x*/'x), Iwao's patchiness regression, exponent k, the chi-square values with degrees of freedom, the probability of fit, and mean clump size C\.) representing the within tree and overall distribution pattern of D. curi are presented in Table I ~....-~ Variance/.. binomial dfvariance ding crowindex nent patchi- 52 'k' Probability Lloyd's ness Expo- of (S'/X) Negative binomial fit of ClU~lP x:s X(A) S1ZC for (x*) negative TABLE 1. Spatial di:>tribution of citnts psylla eggs on acid Hme on == x'" == X o S'

3 SPATIAL DiSTRiBUTION OF CITRUS PSYLLA 321 The data presented in Table 1 revealed that variance exceeded. the mean in all the sets, indicating a contagious or aggregated distribution of eggs. The mean crowding values exceeded the mean density, and thereby LLOYD'S (1967) index of patchiness became j?;l'cater than unity in all cases, which confinl1cd the aggregation pattern. The trend was further reflected by the exponent k \vith values ranging from 0.13 to 0.99 in the different sets of data. To understand the distribution further, IWAo's (1968) patchiness regression "vas fitted based on the linear relationship between mean crowding and mean density, over a range of different densities. x*=(a+ 13-;) which worked out to x* = :~. The value of the index of basic contagion (ex :::<: 8.93) being greater than 0 indicated a positive association between individuah in a colony and (fj) the coefficient of density contagiousness being greater than one confirmed the aggregation among colonies. The causes of aggregation for the population described by the negative binomial dis tribution were explained by mean clump size (X). Among the sets, the clump size was varying (both below and above two). The average of 3.15, however, rc:flccted the role of both environment and oviposition behaviour in the aggregation pattern of eggl). The results of the analysis of variance of tbe mean population density (Table 2) revealcd that the four directions did 110t Siglli~ ficantly affect population density. The populations in the four directions were correlated with the total population (Table 2). Those of thc three directions (West, North and South) were highly correlated (at 1%) whereas east was significant at 5 % level. Thus any direction could be sampled from the point of view of accuracy and feasibijity. Spatial distribution of nymphs: The variance was greater than the mean, which.indicatcd an aggregated distribution. TABLE 2. Analysis of variance and correlation of section and total tree population. DirectiOIls Average nymph _.~..-.- ~ _._ ~- East CorrelatIOn with Average egg total ('r') O.92H 0.87-:<* 0.65* *~' (1.23) (0.79).27) R6) Correlation with total ('r') Average adult Correlation with total ('f') 0.94*'" o 09 88** 50 (-0.52) (-0.44) (-0.63).46) ** 0.91"* NS. N.S. N.S. N.S. * Not significant. Significant at 5 %. Significant at 1 %.

4 322 B. DHARAJOTHI El' AL. The index of mean crowding exceeded the mean density and therefore, LLOYD'S (1967) in.dex of patchiness was greater than unity in all the sets showing that the nymph population followed a contagious distribution. This was further confirmed b}' the 'k' values. The IWAO'S (1968) patchiness regression equation was calculated (x;* x) by which also the aggregated distribut:on was confirmed (Tables 3 and 4). In 60 % of the cases the clump size was less than. 2, probably mfluenced by the limited supply of young shoots on which the nymphs congregate and feed. Statistically significant differences were not observed in the mcan population densities among the four directions, based 011 analysls of variance. The population from East, North and South were highly correlated with toial population. However, West shmved no cotrclation (Table 2). Spatial distribution of adu/ ts: In the adult population of psylla, 30 ~~ of the trees showed a tendency to aggregation. and the remaining showed random distribution. with variance-mean ratio almost equal to one (Table 5). The Lloyd's index of patchiness did not show consistency in this eascl hence variance mean ratio and 'k' values were used to explain the distribution. Overall pooled distribution, however conformed to aggregation. Further, the adult population. did not show any significant correlation with total from any direction (Table 2). Sample sizes: The optimum number of shoots required for a reasonably accurate estimation of the egg population at 10% and 20 ~,~margins of error (d) with reference to the mean at 5 /~ value of the confidence limits (t-value) were 40 and 39 per tree (Table 4). A sample of TABLE 3. Spatial di~tnbllti()n of cill'us psylla nymphs on acid lime. Tree No. (x) Variance! (st)' VarIance( (S!I(50 ratio ~.-~ ~. Expo~ nent 'k' crowding (x*) Lloyd's index of Patchiness Negative Probabiltty binomial of fit for negative X 2 df binomial clump size 0,) «) o \ R SS o10 \8 J 0.67 o \ \ X.

5 SPATIAL DISTRIBUTION Of' CrrRUS PSYLLA 323 SI. no. off ~ TABLE 4. Optunum sample number/tree for field,estimation of psyl1a population. 5% t value Egg Nymph Pcm issible margins of error Permissihlc margins of error % Spatial % ] % 10~~ distribution of citrus psylla adults on acid lime. Adult _.~_..._ permissible margins of error - Jwao'<;Patchiness o (5<) 02 VarianC'..e Patchiness (S'/x) Lloyd's crowding (x>1") mt'.an lndex l.00 (SS) Exponent ~ , () o Equation x* 'k' = "rr._ ratio """_ of 9.87 x'.... of Variance -..-~

..~ 324 B. DHARAJOTHI ET AI... 40 shoots/trce at 10 % margin of error and at 5 % t value is reasonably good for survey and control studies (SOUTHWOOD, 1978).

6 ..~ 324 B. DHARAJOTHI ET AI shoots/trce at 10 % margin of error and at 5 % t value is reasonably good for survey and control studies (SOUTHWOOD, 1978). Among the samples of 39 and 38 shoots/ tree at 10% and 20 % margins of error at 5 % t-valuc, 38 shoos/tree at 20 % margin of error at 5 ~~ t-value (Table 4) is applicable for population estimation studies: In the case of adults a sample of 19 shoots/ tree at 10 % margin of error at 5 % t-value (Table 4) can he taken as the optimum samp!e size. The present study on the spatial distribu~ tion of D. curi revealed that eggs and nymphs followed contagious distribution which also reported by WANG (1981) in the case of D. citri in. Taiwan. The distribution of adults did not show definite pattern. However from pest management point of view, the eggs and nymphal stages matter most, because immediately after hatching, the nymphs start sucking the sap from the plant. So any control strategy needs to be directed at early stages. Egg sampling, therefore, is crucial to fix a time of spray. The trend of the pest to change from an early aggregated distribution to random distribution in, adults indicates the role of key mortality factors operating. This, therefore, opens new vistas in the study of D. citri for which the sampling plan outlined here will be applicable. ACKNOWLEDGEMENTS We thank Dr. R. M. PANDEY, Director, Indian Institute of Horticultural Research, Bangalore for providing facilities and Mr. G. S. PRASADA RAo. (Scientist-2, Statistics) for analysing the data. The help rendered by Mr. B. B. BOPAIAH and Mrs. S. HANUMANTHARAYAPPA in the maintenance of the citrus orchard is duly acknowledged. REFERENCES ARBOl1S. A. G. & J. E. KERRICH (1951) Accident statistics and concept of accident pronenc'),\. Biometrics, 7, BINf>RA O. S. (1966) Role of insects and other animals in relaion to citrus decline. Pw~iab Hart.. r., 6, BINDRA. O. S. (1969) Controlling citrus pests. Indian Hart.. 13 (2), 28~31. BINDRA, O. S. (1970) Insects, 64-78, ill: Cillll's Decline in India-Causes alld Control (ed. CHADHA et aj.), Jt. Pub!. of PAUjOSU/USAID, Ludhiana, PW1jab, India. BHUI ANI, D. K. (1979) Inscct pests of citrus and their control. Pesticides, 13 (4), 15--2]. CAPOOR, S. P., D. G. RAO & S. M. VISWANATH (1967) Diaphorilla curf Kuway, a vector of the greening disease of ctirus in India. llldiall J. agrlc. Sef., COCHRA~, W. G. (1977) Sampling Technique:>', 2nd ed. Wi1cy, New York, 413 pp. TWAO, S, (1968) A new regression method for analyzing th~ aggregation pattern of animal populations. Research un population Ecology, 10, J-20. LLOYD, M. (1967) crowd mg. J. Anim Ecol.. 36, SOUTIlWOOD, T. R. E. (1978) Ecological Methods. Methuen and Co. London, 391 pp. WANG, C. L. (19Hl) Ecological studies of Asmtlc citrus psyllld (DiapllOrina citri K) with special reference to its spatial distnbution. J. agrie. Res. Chil/a., 30 (4).412-4)9.

International Journal of Education and Research Vol. 1 No. 1 January 2013 DISTRIBUTION OF SPITTLEBUG NYMPH

International Journal of Education and Research Vol. 1 No. 1 January 2013 DISTRIBUTION OF SPITTLEBUG NYMPH 1 SOMNATH BHAKAT, 2 PRADIP DEY & 3 ARUP KR. SINHA 1,2,3 Department of Zoology, Rampurhat College,