Abstract

The life table of rice BPH was studied under field and natural enemy free condition on three rice varieties viz., PTB33, Udaya and TN1 representing resistance, moderate resistance and susceptibility to BPH respectively. Under field condition, BPH mortality was very high in all the three varieties and all the growth stages starting from egg to adult stage due to high predation of spiders and to lesser extent by mesovelid bugs and Dryinids. The population trend index was low, recording 0.72, 2.11 and 2.15 respectively for PTB33, Udaya and TN1, whereas, it was higher recording 13.20, 22.28 and 25.55 respectively under natural enemy free condition. BPH population assumed a near type II diagonal survivorship curve. Mortality survival ratio (MSR) was the highest for the 1 st and 2 nd instar BPH and as the insects grew, MSR values gradually dwindled and again at 5th instar stage there was a rise. Indispensable mortality (IM), at egg stage was maximum followed by early instars in all the three varieties examined and was minimum during late instars and adult stages.

Keywords: Life table, brown planthopper, kharif, spiders, survivorship curve