Submitted to: American Bee Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2000
Publication Date: N/A
Interpretive Summary: The varroa mite is the most serious of pests attacking the honey bee in the U.S. Much emphasis has been placed on developing natural compounds for varroa control in recent years. Compounds that are present as a result of burning grapefruit leaves were investigated in our study. Extracts of leaves and extracts of collections of smoke were not causing varroa to detach from their bee hosts. The residue that collected on the inner surface of a desiccator, used as the burning chamber, did cause significant numbers of mites to fall from infested honey bees. It is possible that such a residue may be deposited on honey bees and cause varroa to detach, as seen in bioassays. This residue material consisted almost completely of phenolic compounds. One phenolic compound, in particular, was active in affecting varroa.
The varroa mite, Varroa jacobsoni Oud. (Acarina: Varroidae), is the most serious parasite of honey bees, Apis mellifera L. (Hymenoptera: Apidae) in the U.S. Varroa immatures and adults feed on bee hemolymph, causing morphological abnormalities and transmitting debilitating viruses. Without control efforts by man, varroa eventually destroy the colony within ca. 2 years. Blowing smoke from burning of grapefruit leaves over varroa-infeste honey bees has been shown to cause biological activity on the varroa: after exposure, varroa detach and fall from their honey bee hosts. Such detachment of varroa and falling to the hive floor during cooler weather could provide substantial control of the varroa since many varroa are unable to crawl back to the cluster of bees. We investigated the compounds involved in producing this biological activity by grapefruit leaves. Extracts were made of whole leaves, smoke collections and residue from a desiccator used as the burning chamber. Bioassay of these three separate extracts indicated that the residue from the burning chamber contained the compounds most active in varroa detachment. Analysis of this residue by gas chromatography/mass spectrometry revealed that most of the constituents were phenolic compounds. It is possible that such residues can be deposited on treated honey bees, causing the mites to detach. Bioassay of these individual compounds showed that the phenolic 3-methylphenol was most active in causing varroa to detach from bees in the laboratory. Discussion is given on the role of other phenolic compounds in the control of arthropod pests.