Efficacy of Chemical and Bio-Rational Insecticides Against Cotton Leaf Worm (Spodoptera littoralis) in Soybean

Document Type : Original Article

Authors

1 Food Legumes Reserarch Department, Field Crops Research Institute, Agricultural Research Center, Giza. Egypt.

2 Department of Vegetable and Ornamental Pests, Plant Protection Research Institute, Agricultural Research Center, Giza. Egypt.

3 Seed Technology Research Department, Field Crops Research Institute, Agricultural Research Center, Giza Egypt.

Abstract

The cotton leafworm, Spodoptera littoralis, poses a significant threat to soybean production in Egypt, prompting a search for the insect control using sustainable alternatives to conventional chemical insecticides. This study aimed to evaluate the efficacy of a chemical insecticide (indoxacarb), a bio-pesticide (Bacillus thuringiensis - Agerin), and a botanical extract (lemongrass) on three soybean varieties (Giza 111, Giza 35, and Crawford) for managing S. littoralis and to assess their interactive effects on pest mortality, agronomic performance, and seed quality. Field experiments were conducted over two seasons (2021-2022) using a split-plot design. Results showed that while indoxacarb caused the highest larval mortality (94.38-95.48%), the bio-pesticide Agerin (84.81-86.15%) and lemongrass extract (74.89-76.25%) were also highly effective. The varieties Giza 111 and Giza 35 caused high mortality to larvae of S. littoralis compared to the susceptible Crawford variety (the insect susceptible check). Regarding yield, bio-rational treatments performed comparably or superior to indoxacarb. Giza 111 was the highest-yielding variety, and its combination with lemongrass or Agerin produced the highest seed yield (up to 1.99 ton/fad). Notably, Agerin and lemongrass treatments significantly enhanced seed quality, increasing protein and oil content, whereas indoxacarb application resulted in a significant reduction in protein content compared to the control. This study concludes that an integrated strategy combining the insect tolerant, high-yielding Giza 111 variety with the bio-pesticide (Agerin or lemongrass extract) is an effective and sustainable approach for managing S. littoralis, maximizing both yield and seed quality while avoiding the negative impacts of chemical insecticides.

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