ROY S., GURUSUBRAMANIAN G.
Abstract
This study was conducted to determine dose-mortality response of the three sucking pests of tea: Helopeltis theivora Waterhouse,
Scirtothrips dorsalis Hood and Empoasca flavescens Fabricious, to neem formulation of varying azadirachtin content (300, 1 500, 3
000, 10 000 and 50 000 ppm) under field conditions. Of neem formulation tested, 50 000 ppm and 10 000 ppm had the lowest LC50
values, highest slopes and relative potencies for the three target pests. Among the three sucking pest species studied, S. dorsalis was
highly susceptible to neem formulation of varying azadirachtin content as revealed by the lower LC50 values (0.09 – 0.20 ppm),
highest slopes (1.99-2.54) and mean percent reduction (46.8-75.8%) followed by E. flavescens (0.12-0.39 ppm; 1.92-2.38; 46.3-
64.5%) and H. theivora (0.16-2.27 ppm; 1.48-2.25; 34.8-54.1%). LC50 decreased as the azadirachtin content of neem formulation
was increased. Pest damage (evaluated in terms of mean % reduction of pest population) was lessened as the concentration of
azadirachtin (tested dose) increased. The present study, however, revealed the fact that azadirachtin concentration is the determining
factor in terms of its bioactivity, i.e., in controlling the pest. The bioactivity of azadirachtin concentration may vary from insect to
insect but in tea, using of 50 000 ppm azadirachtin is ideal for managing the three major sucking pests.
Key words:
Azadirachta indica A. Juss; bioactivity; field conditions; mortality; population count; Helopeltis theivora; Scirtothrips dorsalis; Empoasca flavescens