Influence of abiotic and biotic factors on population dynamics of BPH (Nilaparvata lugens Stal) and GLH (Nephotettix virescens Distant)

Sucking pests of rice, particularly brown plant hopper and green leaf hopper, cause major damage apart from the disease transmission. They are the regular pests and in certain parts of country severe outbreaks were observed to cause heavy damage. Environmental factors play a major role in population build-up and outbreaks of sucking pests during a cropping season. However, biotic factors like natural enemies play a significant role in suppressing the population upsurge of sucking pests. Keeping these points in view, an experiment was laid out to study the influence of environmental factors viz., abiotic and biotic factors (natural enemies) on BPH and GLH. The results revealed a positive significant correlation of pest population build-up with the temperature. However, the morning RH was negatively correlated with both BPH and GLH. A significant positive correlation was obtained with spiders and mirid bugs for both BPH and GLH during initial phase of pest population build-up. The influence of abiotic factors on natural enemies was also found to be same as that on pest indirectly indicating influence of weather parameters on host population. Furthermore, ratio of predator to pest was also calculated which showed that spiders being a generalist predators were abundant than mirid bugs and their population fluctuated less with pest population than mirid bugs. It was ascertained that both abiotic and biotic factors played major role in population fluctuation especially humidity, high temperatures with intermittent rainy days favoured rise of pest population. However, the biotic factors like natural enemies and pest population are highly interdependent.