Source: CropBiotech Update

The cotton bollworm, Helicoverpa armigera (Hubner), is one of the most devastating pests of cotton, cereals, and food crops worldwide. Farmers control this pest through chemical means, but indiscriminate use of these control methods can also lead H. armigera to develop resistance to insecticides. It is thus important to determine what agro-climatic conditions determine the effectiveness of insecticides, as well as their coordinated use with insect-resistant transgenic crops, so that farmers may still be able to practice sustainable crop production.

H.C. Sharma and G. Pampapathya of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) report on the “Influence of transgenic cotton on the relative abundance and damage by target and non-target insect pests under different protection regimes in India.” Their work is published in a recent issue of Crop Protection.

Scientists grew transgenic cotton hybrids, their conventional counterparts, commercial varieties, and indigenous cotton under insecticide protected and unprotected conditions during the 2002-2004 rainy seasons. They then measured egg and larval density, damage to various cotton plant parts, seed cotton yield, and the effect of transgenic cotton and insecticides on non-target insect pests.

Major findings include the following:

1. there were no significant differences in egg-laying behavior of H. armigera under both protected and unprotected conditions;
2. there were fewer larvae on transgenic hybrids, but only in conditions of high infestation;
3. with few exceptions, bollworm damage in squares and bolls was significantly lower in the transgenic cotton hybrids than in the non-transgenic ones;
4. there were no significant differences in seed cotton yield under moderate infestation levels, but yields of transgenic hybrids were significantly greater during high infestation; and
5. there were no differences between transgenic and non-transgenic hybrids in their relative susceptibility to the cotton jassid, serpentine leaf miner, white fly, green bug, ash weevil, and red cotton bug.

According to the authors, results suggest that it would be useful to combine transgenic resistance to H. armigera with plant characteristics conferring resistance to the target or non-target insect pests in the region in order to realize the full potential of transgenic plants for sustainable crop production.

Subscribers to the journal can read the complete article through http://dx.doi.org/10.1016/j.cropro.2005.11.002.