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Title: Two strains of Pseudomonas fluorscens bacteria differentially affect survivorship of waxworm (Galleria mellonella) larvae exposed to an arthropod fungal pathogen, Beauveria bassiana

Author
item Meikle, William
item BON, MARIE-CLAUDE - European Biological Control Laboratory (EBCL)
item Cook, Steven
item Gracia, Carlos
item Jaronski, Stefan

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2012
Publication Date: 1/9/2013
Citation: Meikle, W.G., Bon, M., Cook, S.C., Gracia, C.G., Jaronski, S. 2013. Two strains of Pseudomonas fluorscens bacteria differentially affect survivorship of waxworm (Galleria mellonella) larvae exposed to an arthropod fungal pathogen, Beauveria bassiana. Biocontrol Science and Technology. 23(2): 220-233.

Interpretive Summary: In a field experiment by the same senior author (Meikle), biopesticide (which is like a pesticide but instead of chemicals it uses live fungal spores to attack pests) that had been commercially produced had very little effect on the bee mites (Varroa) that the product was trying to treat, and a negative effect on the nontarget insects, the bees themselves. This result was very different from previous field trials. The biopesticide was found to be contaminated by two strains of a bacteria that are often found in spoiled food and unclean water. The question was whether the bacteria may have interfered with the fungal spores and their ability to kill the mites. The authors found that the bacteria did affect how well the fungal pathogen infected its host. Insects treated with one of the bacterial strains and then the fungus often lived longer than insects treated with just the fungus, which means the bacteria somehow interfered with infection or slowed the growth of the fungus. When only bacteria were applied, they did not affect how long the insects lived. This result shows how important it is to make sure that biopesticide products do not have high microbe contaminations.

Technical Abstract: Two strains of Pseudomonas fluorescens were found contaminating a biopesticide used in a previous study against Varroa destructor infestations in honey bee hives. In the aforementioned study the biopesticide, a formulation of the arthropod pathogen Beauveria bassiana, failed to have any impact on the mite infestation despite successful results in previous studies. The objective of the present research was to determine whether the bacteria may have interfered with the infectivity and/or virulence of the arthropod pathogen, Beauveria bassiana, used in the biopesticide. Galleria mellonella late instar larvae treated topically with both a bacterial suspension of 6.8 to 7.0 x 10**7 cfu per ml and a conidial suspension of 2.5 x 107 or 2.5 x 10**8 B. bassiana conidia per ml showed, in the case of one of the bacterial strains, significantly increased survivorship compared to larvae treated with just the B. bassiana suspension. In a second series of experiments in which the larvae were immersed in a bacterial suspension prior to application of the B. bassiana suspension, which was applied using a spray tower, a significant effect of the same P. fluorescens strain on larval survivorship was observed at 2.5 x 10**8 conidia per ml. In none of the experiments did either bacterial suspension by themselves or blank control solutions have an impact on larval survivorship. These results show that an interaction between the bacteria and the pathogen may explain some of the results from the prior field trial. Further work on temperature effects is needed.