FEEDING-BEHAVIOR AND GROWTH OF HELIOTHIS-VIRESCENS LARVAE ON DIETS CONTAINING BACILLUS-THURINGIENSIS FORMULATIONS OR ENDOTOXINS

Bacillus thuringiensis (Bt), spore/crystal mixtures, and purified Bt endotoxins were tested for effects on Heliothis virescens (F.) growth and behavior by use of diet-incorporation bioassays. Larvae were exposed to three basic diet treatments: 1) feeding arenas containing only normal artificial diet, 2) feeding areas containing only a diet of B. thuringiensis formulation or endotoxin, and 3) feeding arenas where larvae could choose between normal diet and diet containing a Bt formulation or endotoxin. Young larvae avoided Bt formulations and Bt-endotoxin-containing diets. Even concentrations of formulations and Bt-endotoxins that did not cause mortality or severely inhibit growth of young larvae caused avoidance. Fourth and fifth instar larvae avoided formulations and endotoxin-containing diets when the concentrations used inhibited growth. Purified endotoxins produced by transformed E. coli cells caused avoidance similar to the spore/crystal mixture in Dipel.