Key Words

Bt cotton, Population dynamics, sucking pests

Introduction

Cotton (Gossypium spp), the white gold of India is one of the important commercial crop and greatly contributes to national economy. The insect pest constitute one of the major limiting factors in the production as the crop is vulnerable to attack by about 162 species of insects and mites (Satpute et al., 1988).

Already commercialized transgenic Bt cotton offer an opportunity to contain the bollworm problem, but the cultivation of the crop under diversified agro climatic situations makes the crop to suffer a lot by different kinds of pests and diseases. Large area under rain fed situations and extensive replacement of conventional varieties with superior hybrids makes the crop easily vulnerable to insect sucking pests. Among the key pests of cotton, the cotton leafhopper, Amrasca biguttula biguttula (Ishida) (Homoptera: Cicadellidae) is an alarming pest throughout the crop growth. The nymphs and adults suck the sap from leaves and cause phytotoxic symptoms known as hopper burn which results in complete desiccation of plants and has become one of the limiting factors in economic productivity of the crop. (Shivanna B K et al 2009)

A good cotton crop with minimal pest attack brings prosperity, while severe incidence brings misery. Thus pest is an important determinant of the prosperity of the cotton farmers. The knowledge about incidence of pest during the cropping season and its possible dynamics help in designing pest management strategies (Santhosh et al.,2009). Hence the present study on population dynamics of leaf hopper, Amrasca bigutula bigutula (Ishida) was undertaken during the Kharif seasons of 2009-10 and 2010-11.

Materials and Methods

Field experiment was carried out in Wyra and Thallada area of Khammam District. This region is geographically located in Central Telangana agro climatic zone of Andhra Pradesh. The complete experiment was carried out in farmer’s fields by following all standard agronomical practices under semi irrigated conditions.

The sowings were done on last week of june to first week of July in both seasons. The observations recorded randomly selected 25 plants per each genotype at fortnightly intervals till the harvest of the crop from the beginning. The observations of leaf hopper populations were counted on three leaves selected randomly from top, middle and bottom, 15 days after sowing and later calculations worked out per leaf per plant.

The selected Bt genotypes in the study were Brahma Bt, Dyna Bt, NCS-207 Mallika Bt, NCS

145 BG II (Bunny), Akka BG II in 2009-10 season and VICH 15 BG II, MRC 7929 BG II, NCS 207 BG II, RCH 533 BG II, Tulasi 7 BG II in 2010-11 season. The Bt genotypes selected in the experiment are incorporated genes coding for Cry 1 Ac (Event MON 531) and Cry1Ac + Cry2Ab (Event MON 15985).

Results and Discussion

Field experiment was carried out in Wyra and Thallada area of Khammam District. This region is geographically located in Central Telangana agro climatic zone of Andhra Pradesh. The complete experiment was carried out in farmer’s fields by following all standard agronomical practices under semi irrigated conditions.

The sowings were done on last week of june to first week of July in both seasons. The observations recorded randomly selected 25 plants per each genotype at fortnightly intervals till the harvest of the crop from the beginning. The observations of leaf hopper populations were counted on three leaves selected randomly from top, middle and bottom, 15 days after sowing and later calculations worked out per leaf per plant.

The selected Bt genotypes in the study were Brahma Bt, Dyna Bt, NCS-207 Mallika Bt, NCS 145 BG II (Bunny), Akka BG II in 2009-10 season and VICH 15 BG II, MRC 7929 BG II, NCS 207 BG II, RCH 533 BG II, Tulasi 7 BG II in 2010-11 season. The Bt genotypes selected in the experiment are incorporated genes coding for Cry 1 Ac (Event MON 531) and Cry1Ac + Cry2Ab (Event MON 15985).

Table: Fortnightly mean population of leaf hopper on transgenic Bt Cotton