Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 19, 1999
Publication Date: January 20, 2000
Citation: Siegel, J.P., Tebbets, J.S., Vail, P.V. Prevalence and transovum transmission of bacillus thuringiensis berliner ina navel orangeworm colony. Journal of Invertebrate Pathology. Volume(75):171-173. Interpretive Summary: Bacillus thuringiensis (Bt) has sporadically killed many caterpillars (>15%) in our navel orangeworm (Ameylois transitella (Walker) colony. Bt was recovered from both living and dead individuals. The number of caterpillars containing Bt and killed by Bt changed, and by June 1998 only 2% of the samples from our colony jars contained Bt. The method(s) by which Bt entered and was maintained in the colony was investigated and we demonstrated that Bt survived on the eggs. This is interesting because the A. transitella eggs were soaked in a 5% formaldehyde solution, which should have killed all bacteria. Further experiments demonstrated that Bt on the surface of eggs could survive soaking in a 5% formaldehyde solution for as long as 60 min. However, a 10% formaldehyde solution successfully killed all the Bt on the egg surface. Our results suggest that Bt remained in our colony because our method of surface sterilizing eggs did not work. We now wrecommend using a 10% formaldehyde solution instead.
Technical Abstract: Bacillus thuringiensis (Bt) was isolated in December 1997 from an outbreak in a navel orangeworm, Amyelois transitella (Walker), colony. This bacterium was recovered from both cadavers and apparently healthy individuals. The prevalence of Bt varied, and by June 1998, only 2% of the colony jars contained Bt. Avenues by which Bt entered and was maintained in the colony were investigated, and transovum transmission of Bt was demonstrated. This is noteworthy because the A. transitella eggs were surface-sterilized with a 5% formaldehyde solution. Further experiments demonstrated that Bt associated with eggs could survive immersion in a 5% formaldehyde solution for as long as 60 minutes. However, a 10% formaldehyde solution successfully surface-sterilized the eggs. A Hewlett- Packard microbial identification system was used to examine the relationship among the different Bt isolates recovered. Isolates obtained from eggs were indistinguishable from an isolate obtained from larvae. We conclude that Bt maintained in our colony because a 5% formaldehyde solution was ineffective. We recommend that a 10% formaldehyde solution be used instead for surface-sterilization to reduce the incidence of Bt infections.