JUVENILE-HORMONE ESTERASE-ACTIVITY AND ECDYSTEROID TITER IN HELIOTHIS-VIRESCENS LARVAE INJECTED WITH MICROPLITIS-CROCEIPES TERATOCYTES

Juvenile hormone esterase (JHE) activity in the hemolymph of 5th-instar Heliothis virescens larvae injected with Microplitis croceipes teratocytes was inversely related to the number of teratocytes injected. JHE activity in the hemolymph of larvae injected with 750 3-day-old teratocytes (the approximate number from one parasitoid embryo) was depressed to less than 5% of those levels found in control larvae. During the latter portion of the digging stage and in the burrowing-digging (BD) stage JHE activity in larvae treated with 350 teratocytes was approximately 40% of control values. However, injection of 180 teratocytes did not significantly affect JHE titers. Two-day-old teratocytes caused the greatest reduction in JHE titer with decreasing effects observed with injections of 3- to 6-day-old teratocytes. Nevertheless, because 2-day-old teratocytes were difficult to separate from host hemocytes, 3-day-old teratocytes were used in most of these studies. Injections of nonparasitized H. virescens hemolymph plasma, Micrococcus luteus bacterial cell walls, washed M. croceipes eggs, or teratocytes from Cotesia congregata did not depress JHE titers. Teratocyte injections also significantly reduced growth of host fat body. Ecdysteroid titers in cell formation, day 2 (CF2) larvae injected as new 5th instars with 350 3-day-old teratocytes failed to increase, as compared to noninjected and saline-injected controls. An injection of 1-mu-g/larva of 20-hydroxyecdysone at the BD stage permitted normal pupation in 50% of the teratocyte-treated larvae as compared to 0% pupation for teratocyte-treated control larvae not treated with 20-hydroxyecdysone. Teratocytes seem to be responsible for the inhibition of JHE release and thus indirectly impact on ecdysteroid titers.