Determination Of Attractant Semio-Chemicals Of The Wax Moth, Galleria Mellonella L., In Honeybee Colonies
The role of honeybees remains crucial in global food security, ecosystem stability and poverty alleviation. However, recent reports indicate a global decline in population of both the feral and domesticated honeybees. The decline is attributed to interaction of myriad drivers including: climatic changes, intensive application of pesticides, habitat alteration, pathogen and diseases, and pest which often act in synergy. Pathogens and pests have been undoubtedly identified as key drivers. Amongst honeybee pests, the greater wax moth, Galleria mellonella, has been reported as the most devastating pest. The greater wax moth larvae feed on pollen, honey, wax and occasionally brood. Larvae tunnel through the comb structure, leave masses of web, which result in galleriasis, bald brood and absconding of colonies. Several management strategies including physical, biological and chemical are applied against greater wax moth invasion of honeybee colonies and honeybee product stores, but all have short comings that limit their application. There is scarce information regarding its chemical ecology, thus, determination of semio-chemicals involved in the wax moth behaviour is crucial. In the current study, laboratory raised colony of the wax moth was used to elucidate larva aggregation pheromones and adult female host kairomones. Dual choice assays using Y-tube olfactometer revealed significant attraction of immature instars to only food and frass volatiles, while mature instars were strongly attracted to conspecific cocoon-spinning larva odors only. Analyses and identification in a coupled gas chromatography-mass spectrometry (GC-MS) using NIST libraries revealed presence of three alcohols, alkane and aromatic hydrocarbons in frass and feces volatile extracts, while food extracts in addition to the three classes of compounds in frass, have a ketone, lactone, three monoterpenes and four sesquiterpenes. Furthermore, analysis of cocoon-spinning larva volatile extracts revealed presence of two aldehydes and two alkanes. Wind-tunnel bioassays showed that only mated females significantly respond to honeybee comb odors. Analysis of honeybee comb volatile extracts revealed presence of various classes of organic compounds. However, further analyses in GC with both flame ionization (FID) and electroantennographic detection (EAD) revealed that only 7 compounds viz ethyl propanoate; 2-methyl, ethyl propanoate; ethyl 2-methyl butanoate; 3-methyl butyl acetate, nonanal ,decanal and sylvestrene elicited antennal response in mated female. These results demonstrate that honeybee hive related semiochemicals play crucial role in chemical communication of G. mellonella both at larval and adult stages. Further, the results offer a benchmark in developing semio-chemically based management and control system for the pest.
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