Factors Affecting Juvenile Hormone Analogue Activity in the Tobacco Budworm12

Abstract

Tests showed last instars of Heliothis virescens (F.) to be the larval stage most sensitive to juvenile hormone (JH) analogues based on morphological defects in the pupal stage. Peak sensitivity of the last in star to a JH analogue appeared 2 days after ecdysis, When treating last instars, greater effects (up to 10-fold) were observed when the same dosage was extended over a 3-day period. Intrahemocoelic injections of a JH analogue produced fewer deformities than topical applications. Comparing 2 posttreatment temperatures, the higher gave a 2 to 9-fold increase in effectiveness over the lower temperature. Differences in tolerance to JH analogues were shown to exist in 2 strains of tobacco budworms. The insecticidally resistant strain proved to be more tolerant to JH analogues than the susceptible strain. Additional studies revealed that Heliothis eggs also were sensitive to JH analogues based on failure to hatch. These ovicidal tests indicated that sensitivity was greater when eggs were less than 12-hours old.