Juvenile hormone esterase activity and ecdysteroid titer in Heliothis virescens larvae injected with Microplitis croceipes teratocytes

Abstract

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 nonparasitired H. virescens hemolymph plasma, Micrococcus lureus bacterial cell walls, washed M. croceipes eggs, or teratocytes from Coresia 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 pg/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. o 1992 ~i~e y -L i s s , Inc.

Down-regulation of juvenile hormone esterase and arylphorin production inHeliothis virescens larvae parasitized byMicroplitis croceipes

“…1A). These results are consistent with previous observations (Dahlman et al, 1990;Zhang et al, 1992;Fathpour and Dahlman, 1995). Injection of McPDV purified from calyx fluid elicited a similar response (Fathpour and Dahlman, 1995).…”

“…Host juvenile hormone esterase (JHE) activity is reduced in a number of parasitoid-host systems (Beckage and Riddiford, 1982;Dahlman et al, 1990;Hayakawa, 1990;Strand et al, 1990;Zhang et al, 1992). In parasitized insects, hemolymph titers of storage proteins (arylphorins) can be either elevated (Jones et al, 1985(Jones et al, ,1986Jones, 1989;Kunkel et al, 1990) or depressed (Beckage and Kanost, 1993;Shelby and Webb, 1994;Fathpour and Dahlman, 1995).…”

“…Onset of host metamorphosis often is accelerated or delayed, respectively, in these species. In the Heliofhis virescens-Microplitis croceipes system, THE activity and arylphorin titer were reduced significantly in larvae injected with the M. croceipes-associated PDV (McPDV) (Fathpour and Dahlman, 1995, unpublished data) or teratocytes (Zhang, 1992;Zhang et al, 1992). The reduction of host JHE activity and arylphorin levels following parasitism or injection of calyx fluid or teratocytes could be due to selective degradation of these proteins or due to specific inhibition of the translation of the corresponding mRNAs.…”

“…In addition, teratocytes, which are cells derived from the extraembryonic serosal membrane of many braconid parasitoids, are also released into the host hemocoel as the parasitoid hatches (Dahlman and Vinson, 1993). Many effects of parasitization on the hosts, such as altered hormonal titers or regulation, reduced weight gain and altered development, can be mimicked by injection of PDVs (Dover et al, 1987;Wani et al, 1990;Dushay and Beckage, 1993;Shelby and Webb, 1994;Fathpour and Dahlman, 1995) or teratocytes (Zhang and Dahlman, 1989;Wani et al, 1990;Zhang et al, 1992;Pennacchio et al, 1992). Thus, the PDVs and teratocytes appear to play important roles in altering host growth and development, although the precise mechanism(s) of host regulation remain unclear.…”

Antibiosis‐type insect resistance in transgenic plants expressing a teratocyte secretory protein (TSP14) gene from a hymenopteran endoparasite (Microplitis croceipes)

“…Teratocytes inhibit host insect growth and development and cause immunosuppressive conditions in some species (Dahlman and Vinson, 1993;Zhang and Dahlman, 1989;Zhang et al, 1992Zhang et al, , 1997.…”