The effects of environmental and biological factors of juvenile hormone analogs on Heliothis virescens (F.)

The effects various environmental and biological parameters have on the activity of juvenile hormone (JH) analogs in the tobacco budworm, Heliothis virescens, ( F.), were studied. Preliminary investigations indicate that when last instar larvae are treated, greater derangement of the insect's metamorphic processes can be obtained when a JH analog is applied during the first half of the stadium. Peak activity occurs 2 days following the molt. An even greater effect (up to 10-fold) can be evolked when the same dosage is spread over a several day period. Injections of JH analogs into the hemocoel produced fewer deformities than topical applications. Certain environmental factors appeared to have an important effect on JH activity. Comparative effects produced in two post-treatment temperatures showed that there was a 2-to 9-fold increase in effectiveness in the higher than the lower temperature. The JH activity did not seem to be influenced by a circadian rhythm. Tolerance to JH analogs was shown to exist in the tobacco budworm. One strain (South Florida) which was susceptible to conventional insecticides proved to be susceptible to JH analogs while the other strain (College Station) which was resistant to most insecticides showed resistance to JH analogs. These data suggest JH tolerance may be related to a high level of oxidative enzymes induced by conventional insecticides