www.IndianJournals.com Members Copy, Not for Commercial Sale Downloaded From IP - 14.139.224.82 on dated 25-Oct-2018 POPULATION DYNAMICS OF BEMISIA T ABACI IN OKRA RAKESH KUMAR, R. K. SHARMA, S. R. SINHA AND KIRTI SHARMA Division of Entomology, ICAR-IARI, New Delhi 110012 Email: rakeshcsa8328@gmail.com ABSTRACT Studies on population dynamics of whitefly Bemisia tabaci on okra crop in Delhi revealed two distinct peaks during 2015 (MSW 30, 21.67 whitefly/ 3 leaves and MSW 36, 17.33 whitefly/ 3 leaves, respectively) and 2016 (MSW 32, 19.67 whitefly/ 3 leaves and MSW 36, 14.67 whitefly/ 3 leaves, respectively). The observations revealed that rainfall (with correlation coefficients of -0.493** and -0.678** during 2015 and 2016, respectively) as the most important predictor of population among the abiotic factors evaluated. Both the generalist predators (biotic factors) were found highly correlated and well fitted in the prediction models. Results also revealed that rainfall, coccinellids and spider population jointly had a significant impact on B. tabaci population buildup in okra. Validation tests for the prediction models showed that the optimized prediction model Y= 27.86413 + 0.04872(X 5 ) - 3.1155(X 7 ) (R 2 = 0.766**) and Y= 21.72667 + 0.0209(X 5 ) - 3.48292(X 7 ) + 1.26738(X 8 ) (R 2 =0.781*) predicted B. tabaci population reasonably well. These models could be used for decision making in IPM, but subject to validation to improve their predictability. Key words: Population dynamics, Bemisia tabaci, okra, prediction model, abiotic factors, rainfall, biotic factors, predators, coccinellids, spiders Indian Journal of Entomology, 80(3): 605-608 (2018) DOI No. : 10.5958/0974-8172.2018.00209.2 Okra, Abelmoschus esculentus (L.) Moench, (Lady’s finger) is most valuable vegetable and it is infested by as many as 72 insect pests afflicting quantitative and qualitative loss (Srinivasa and Rajendra, 2003). Being a virus vector (yellow vein mosaic virus), whitefly Bemisia tabaci (Gennadius) is one of the most serious pests of okra (Sastry and Singh, 1975; Fajinmi and Fajinmi, 2006; Mallic et al., 2016 and Poddar et al., 2016). The population buildup of any insect pest in any ecosystem depends on the abiotic factors prevailing and the active biotic factors. So, fluctuations in the pest population occurs throughout the year. Since, the information available on these are scanty, studies to understand the role of biotic and abiotic factors need to be done to facilitate IPM decisions. Hence, the present study on the population dynamics of B. tabaci to bring out the of role of biotic and abiotic factors in okra. MATERIALS AND METHODS The study was carried out at the Division of Entomology, I.A.R.I., New Delhi during kharif, 2015 and 2016. Okra cv. Arka Anamika was sown in an area of 120 m 2 with 60 x 45 cm spacing. The plot was divided into 3 subplots each measuring 6 x 6m, each separated by 1 m interface to reduce the inter-plot variations. Recommended package of practices were followed, and no plant protection measures were taken up. Observations on population of B. tabaci and their natural enemies- coccinellids and spiders were made on 5 randomly selected plants at weekly intervals. Whitefly population was recorded on 3 leaves (lower, middle and upper) from each plant, while coccinellids and spiders was made from whole plant. Coccinellids included mainly Coccinella septempunctata, Coccinella transversalis and Cheilomenes sexmaculatus. The weekly whitefly observation data were subjected to correlation and regression analysis to find out the influence of biotic and abiotic factors on its population dynamics. A step-wise regression procedure was applied using SAS software to get further insights on the most critical biotic and abiotic factors, deploying step by step selection of precise variables which are significantly correlated with whitefly population. Further, a measure of goodness of fit and the values of c-efficient of determination (R 2 ) was calculated for the developed models. RESULTS AND DISCUSSION The incidence of B. tabaci in okra during kharif 2015 and 2016 revealed that its started from fifteen days after sowing, and maximum population was observed during 30th (21.67 whitefly/3 leaves) and