Effect of abiotic factors on population dynamics of insect pests and natural enemies in potato crop

Insect population dynamics studies in potato crop revealed the occurrence of insect pests of different groups among which the major pests viz. Lepidopterans (Helicoverpa spp., Spodoptera spp., and Agrotis spp.) attained population peaks during initial stages of the crop (June- July), whereas scarabids (Brahmina spp., Holotrichia spp.,) were confined to active growing stage of the crop (July- August) which coincided with monsoon showers. A positive correlation was observed between the insect pest trap catch and abiotic factors viz. maximum temperature (‘r’=0.63 and 0.50) and minimum temperature (‘r’=0.60 and 0.52), relative humidity (‘r’=0.62 and 0.20) and rainfall (‘r’=0.22 and 0.19) during the year 2011 and 2012, respectively. The corresponding periodical sampling for natural enemies revealed the occurrence of coccinellids, syrphids, Chrysoperla carnea and parasitoids like Aphelinus abdominalis and Aphidius sp. The association between predators and or parasitoids with the abiotic factors revealed a positive correlation with their population fluctuation but in case of parasitoids, a negative but non-significant correlation was observed with minimum temperature (‘r’= -0.15) and relative humidity during 2011 (‘r’=-0.23) and with rainfall during 2011 (‘r’=0.20) and 2012 (‘r’=0.15) respectively.