Submitted to: Proceedings of Workshop on Global Int Org Biocontrol (IOBC) Working Group
Publication Type: Abstract Only
Publication Acceptance Date: August 1, 1997
Publication Date: N/A
The entomopathogenic fungus Paecilomyces fumosoroseus is currently under development as a biological control agent for the Russian wheat aphid, Diuraphis noxia. If the potential of this pathogen is to be realised its virulence against non-target organisms & compatibility with existing insect natural enemies requires evaluation. This study describes the interactions between P. fumosoroseus & the convergent ladybeetle, Hippodamia convergens Beetles were purchased from a biocontrol company & had been collected from overwintering sites in the Sierra Nevada mountains of CA. Two pathogenicity assays using a single strain of P. fumosoroseus (Mycotech 612) were run against beetles at a range of doses equivalent to the LC50, LC95, field, 2 times field & 10 times field rate for D. noxia. Mortality of beetles due to P. fumosoroseus was higher in the 1st assay reaching a maximum of 22%. In the 2nd assay mortality of beetles due to P. fumosoroseus only occurred at 10 times field rate & reached 6%. All aphids succumbed to disease at doses at & above the LC95. The difference in the 2 assays is thought to be rela- ted to the physiological status of the beetles: beetles in the 1st assay were delayed in transit & suffered temperature & desiccation stresses prior to assay which could have affected their susceptibility. In feeding bio- assays H. convergens never fed on sporulating infected aphid cadavers, though they readily consumed uninfected, dead aphids. They were also able to distinguish between dead uninfected aphids & aphids which had recently died from fungus infection but had no external sporulation: they did not consume fungus-infected aphids. Beetles which foraged in the presence of sporulating aphid cadavers became contaminated with conidia & vectored these to healthy aphids, initiating infection in 50% of the population.