H. M. Graham

Interactions between the tobacco budworm, Heliothis virescens, and the δ-endotoxin produced by the HD-1 isolate of Bacillus thuringiensis var. kurstaki: Relationship between length of exposure to the toxin and survival

Abstract Larvae of the tobacco budworm, Heliothis virescens, which were fed ad libitum for 24, 48, and 72 hr on a diet treated with various levels of the δ-endotoxin produced by the HD-1 isolate of Bacillus thuringiensis var. kurstaki and then transferred to an untreated diet, showed an unexpected capacity to recover from the effects of the toxin, although, as the length of exposure increased, the capacity decreased. Observations on larvae held to emergence indicated that recovery from the toxin was complete. X-ray studies using Ba2+ incorporated into the diet showed that, although the toxin paralyzed the midgut of the treated animals, many animals recovered after the toxin was removed, with food once again passing through the gut.

Laboratory and field cage tests with Bacillus thuringiensis against pink-bollworm larvae

Abstract Newly hatched and mature larvae of the pink bollworm, Pectinophora gossypiella, were susceptible to spores of Bacillus thuringiensis in lactose dusts and in soil-spore mixtures, respectively. The pupation rate of survivors exposed to the spores as newly hatched larvae was inhibited, and pupal weights decreased with increases in concentration of spores. Application of spores to soil in field cages reduced overwintering populations of pink bollworms about 45%.