Influence of Resistant Soybeans on the Susceptibility of Lepidopterous Pests to Insecticides

TLDR: In the laboratory, Heliothis zea (Boddie) larvae that were fed foliage of ED73–371, a genotype resistant to the Mexican bean beetle, Epilachna varivestis Mulsant, weighed less and were more susceptible to methomyl and Bacillus thuringiensis Berliner compared to larvae feeding foliage of the ‘Bragg’ variety.

Abstract: In the laboratory, Heliothis zea (Boddie) larvae that were fed foliage of ED73–371, a genotype resistant to the Mexican bean beetle, Epilachna varivestis Mulsant, weighed less and were more susceptible to methomyl and Bacillus thuringiensis Berliner compared to larvae fed foliage of the ‘Bragg’ variety. No difference was detected in the LD50, of methyl parathion when H. zea larvae were reared on Bragg and ED73–371. Larvae of Pseudoplusia includens (Walker) weighed less and were significantly more susceptible to methyl parathion when fed ED73–371 foliage than when fed Bragg foliage, whereas LD60’s of methomyl and B. thuringiensis were similar on the 2 genotypes. Percent control of field populations of H. zea was greater in ED73–371 than in Bragg soybeans when plots of each genotype were treated with similar rates of methyl parathion or B. thuringiensis . Fewer larvae were found in untreated plots of ED73–371 than in Bragg, indicating a lower natural population in the resistant soybeans.