Modeling population dynamics of Myzus persicae(Sulzer) and its associated parasitoids in bell pepper in relation to climatic factors

Abstract

Effect of climatic factors on population build-up of green aphid, Myzus persicae (Sulzer) and associated parasitoids was studied on bell pepper under protected environment over a period of two cropping seasons. Plants were infested artificially by releasing 1, 2, 4 and 8 aphids per plant on 30 days after transplanting. In summer crop, population of apterous aphids at initial infestation levels of release peaked on 42 days after infestation (DAI) with the population of 986.0, 2304.9, 3267.3 and 4380.5 aphids per plant, respectively. Aphid population remained comparatively low in autumn crop, and peaked between 63–70 DAI in different infestation levels. The population levels differed significantly at all infestation levels in summer crop but was on a par at 1 and 2 aphid levels in autumn crop. Alate formation initiated three weeks after release of aphids in both the seasons. Correlation coefficient between aphid population and climatic factors indicated that the temperature favoured build-up of aphid population positively in summer crop, being significant with minimum temperature only (r = 0.5247; p = 0.05), whereas, in autumn crop, both temperature and relative humidity influenced the population buildup negatively, which being significant with minimum temperature and minimum relative humidity. Predictive model using stepwise regression analysis between aphid and abiotic factors revealed that minimum temperature to contribute significantly in influencing the population in both cropping seasons, being less in summer crop (26.6%) as compared to autumn crop where it contributed to the extent of 45.1 per cent. Three hymenopterous parasitoids namely, Aphelinus asychis Walker, Aphidius matricariae Haliday and Aphidius ervi Haliday were found associated with M. persicae. The parasitoid, A. asychis and Aphidius spp. resulted in parasitization varying from 1.0–13.7 and 0.7–61.4 per cent in different aphid infestation levels in summer and autumn crop, respectively. A. asychis showed negative functional response to M. persicae population, whereas Aphidius spp. responded positively. Except maximum temperature all other environmental factors influenced the parasitization positively in both cropping seasons, being significant with minimum relative humidity (r = 0.6990; p = 0.01) in autumn crop only.