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ARS Home » Pacific West Area » Logan, Utah » Pollinating Insect-Biology, Management, Systematics Research » Research » Publications at this Location » Publication #198880
Title: FIELD TRIALS ON THE MICROBIAL CONTROL OF VARROA WITH THE FUNGUS METARHIZIUM ANISOPLIAE

Author
item James, Rosalind
item HAYES, GERALD - FDACS, GAINESVILLE,FL
item Leland, Jarrod

Submitted to: American Bee Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2006
Publication Date: 11/1/2006
Citation: James, R.R., Hayes, G., Leland, J.E. 2006. Field trials on the microbial control of varroa with the fungus Metarhizium anisopliae. American Bee Journal. November. p.968-972

Interpretive Summary: A variety of chemical controls products are currently available to the beekeeping industry for varroa mite control. However, we find that beekeepers are frequently dissatisfied with the level of mite control they are able to achieve, and a biological control agent could potentially offer an entirely new approach to this problem. The fungus Metarhizium anisopliae is known to be pathogenic to varroa mites, and we previously conducted several field trials with this fungus in bee colonies, but obtained poor, if somewhat variable, results. We have decided that it is time to present our most recent results to the beekeeping industry, due to the great interest that this project has generated. We present here two large field trials designed to determine the best application strategy for the fungus. None of our experiments yielded significant mite control, although we tried high doses and several different application methods. Before a microbial control of varroa product can be developed, more work is needed on production methods.

Technical Abstract: A variety of chemical controls products are currently available to the beekeeping industry for varroa mite control. However, we find that beekeepers are frequently dissatisfied with the level of mite control they are able to achieve, and a biological control agent could potentially offer an entirely new approach to this problem. The fungus Metarhizium anisopliae is known to be pathogenic to varroa mites, and we previously conducted several field trials with this fungus in bee colonies, but obtained poor, if somewhat variable, results. We have decided that it is time to present our most recent results to the beekeeping industry, due to the great interest that this project has generated. We present here two large field trials designed to determine the best application strategy for the fungus. None of our experiments yielded significant mite control. For both experiments, we used application rates that we thought would be more than adequate. First we tried several very different application methods, yet did not obtain good control. Next, we increase the dose nearly nine-fold and sprayed frames in colonies with an aqueous suspension of spores. Some infected mites were recovered from the hives, but the spores survived very poorly after application. Before a microbial control of varroa product can be developed, more work is needed on production methods to produce a spore with an adequate shelf-life. Another possible reason for the poor field control may be that our treatments failed to get the spores into direct contact with the mites, a condition required for infection to occur. The mites are protected from exposure to spores when they are in the brood cells, and when varroa are on the bodies of adult bees, thus it is difficult to get the spores directly in contact with the mite cuticle.