Microbial control of varroa: misadventures in the field

Authors: James, Rosalind; HAYES, G. - FL DEPT AG&CONS,GAINES.FL

Submitted to: Journal of Anhui Agricultural University
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2006
Publication Date: 5/1/2007
Citation: James, R.R., Hayes, G. 2007. Microbial control of varroa: misadventures in the field. Journal of Anhui Agricultural University. 34(2) :162-166

Interpretive Summary: We report six different field trials used to test the potential of using fungi to control varroa mites in honey bee hives. The fungus used was Metarhizium anisopliae, which will infect varroa mites in laboratory tests. Varroa mites are parasites of honey bees, and cause serious damage to the bees, usually leading to the eventual death of the colony. Several treatments are available, but none are very effective, so new, more effective methods are being sought. In our first two field trials, we found that applications of fungal spores to the hives reduced the numbers of mites in the hives and had no adverse effect on the bees. However, in subsequent field trials, we were unable to obtain any varroa control, despite attempting several different application methods, two different strains of the fungus, and testing in different climates and during different times of the year. We conclude that microbial control of varroa using fungi is not likely to be effective unless some way is found to prolong the survival of the spores in the hive environment.

Technical Abstract: We report six different field trials testing the efficacy of Metarhizium anisopliae, an entomopathogenic fungus, against varroa mites in honey bee hives. Varroa mites are parasitic on honey bees and cause serious damage to Apis mellifera colonies. Several control methods are available for varroa mites, none are very effective, so new, more effective methods are being sought. Varroa has previously been shown to be highly susceptible to M. anisopliae infections, and in our first two field trials, we found some efficacy from spore applications. However, in subsequent field trials, we were not able to obtain any varroa control, despite attempting several different application methods, two different strains of the fungus, and testing in different climates and during different phenological states of the honey bee colony. We conclude that microbial control of varroa using fungi is not likely to be effective unless some way is found to prolong the survival of the spores (or other infective units) in the hive environment.