Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 6, 1997
Publication Date: N/A
Interpretive Summary: A tiny wasp (Microplitis croceipes), lays its eggs inside the larvae of the tobacco budworm (Heliothis virescens) a major insect pest of cotton. Young wasps develop inside the worm, eventually killing it. Adult wasps emerge from parasitized worms and continue the cycle by locating new worms to parasitize. Due to its potential use in biological control, mass rearing techniques were developed for the wasp and was studied extensively. These earlier studies revealed a virus disease causing developmental problems and premature death of the wasps. The virus, named Microplitis croceipes nonoccluded baculovirus (McNOBV), has also been extensively studied. The present study examined whether the wasp virus could infect the worms which the wasp parasitizes. Sensitive antibody tests detected the presence of virus in inoculated worms and in infected wasps. Electron microscopy confirmed the presence of virus particles in infected insects. Bioassay confirmed the infectivity of virus in samples collected from test insects. The study found that the wasp virus can infect the tobacco budworm. The study also measured deleterious effects on wasp development in virus-infected worms. Furthermore, healthy virus-free female wasps exposed to virus-infected worms during egg laying, became infected with the virus. These findings indicate that the virus disease could be a serious problem for wasps in the field as well as in rearing facilities, thus complicating biological control programs.
Replication of Microplitis croceipes nonoccluded baculovirus (McNOBV) in Heliothis virescens larvae was detected by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA), transmission electron microscopy (TEM), and bioassay. Five-day-old H. virescens larvae were inoculated intrahemocoelically with 0 (control), 3, or 30 ng virus/larva, and subjected to ELISA, verified by TEM, at various hours after inoculation. The ELISA results showed increases of the absorbance values and the amount of virus particles produced in some inoculated larvae. McNOBV infection was observed in 16.3-33.3% and 66.7-83.3% of larvae inoculated with 3 and 30 ng virus, respectively, 24-96 hr post inoculation. Virus particles were detected in hemolymph, fatbody, and midgut epithelial cells of infected larvae. In bioassay, McNOBV-infected larvae were exposed to healthy, premated, female M. croceipes for oviposition, 10.6% of the M. croceipes females became infected with the virus. Examination of M. croceipes offspring indicated significant decreases (control vs. infected) in larval emergence (75.0 to 39.6%), cocoon formation (68.8 to 31.3%), and adult eclosion (68.1 to 22.2%). McNOBV was detected by ELISA in 25.9% of dead larvae, 45.2% of dead pupae, and 37.3% of the surviving adults of M. croceipes. These results demonstrate McNOBV replication in H. virescens larvae and transmission of McNOBV from infected H. virescens larvae to ovipositing M. croceipes females and their offspring.