Potential mechanism for detection by Apis mellifera of the parasitic mite Varroa destructor inside sealed brood cells

Abstract

Abstract. The parasitic mite Varroa destructor Anderson & Trueman is a major pest of the honeybee Apis mellifera L. throughout the world. Chemical agents currently used for mite control leave contaminating residues and promote pesticide resistance. As an alternative means of control, it would be useful to identify natural substances enabling bees to detect Varroa inside brood cells. These substances could then be used to trigger mite hygienic behaviour by bees.In this study several techniques were used to screen substances that might allow detection of infested brood cells by bees. Gas chromatography-mass spectrometry analysis was performed on substances extracted in dichloromethane from the contents of brood cells. Solid phase microextraction and solid injection were performed on substances obtained from living and dead Varroa, respectively. Electroantennography was performed to assess the sensitivity of olfactory receptors in bee antennae to some of these substances.Principal component analysis based on proportions of cuticular substances allowed discrimination between bees and other cell contents. Foundress Varroa exhibited the greatest dissimilarity to healthy pupae that were used as controls. Immature Varroa and faecal material were intermediate. High molecular weight compounds, mainly dimethylalkanes, were proportionally the most characteristic components of foundress Varroa. This finding suggests that these compounds would be the most apt to induce uncapping of cells infested by Varroa. Solidphase microextraction and solid injection demonstrated the presence of aliphatic acids, esters, and one alcohol, eicosenol, in Varroa. Electroantennographic recordings showed that mite-resistant bees were more responsive to some acids and one ester. We speculate that these compounds may be involved in recognition of living Varroa by honeybees.

A semiochemical from brood cells infested by Varroa destructor triggers hygienic behaviour in Apis mellifera

“…This finding was already noted by Nazzi et al (2002); whereas Martin et al (2002) did not study hydrocarbons shorter than 21 carbon atoms.…”

“…Stimuli coming from both the mite and the brood have been considered in previous research. Results presented by Aumeier and Rosenkranz (2001) and Martin et al (2001Martin et al ( , 2002 suggest that polar compounds from the mite cuticle may trigger hygienic behaviour. Spivak and Downey (1998) and Gramacho et al (1999) showed that body fluid from bee brood is a strong stimulus for the bees to remove treated pupae.…”

Varroa-specific hygienic behavior of Apis mellifera scutellata in Kenya

“…The strong effect of the number of mites on the expression of hygienic behavior is an indicator for the involvement of chemicals in the recognition of mites infesting cells (Nazzi and Le Conte 2016;Plettner et al 2017). VSH bees were more responsive to manipulated brood cells singly introduced with ten mites in a patch of neighboring brood cells as compared to those singly introduced with five mites in a patch of neighboring brood cells probably because the chemical signals that triggers hygienic behavior are less concentrated and harder to detect in brood with low infestation rate (Masterman et al 2001;Martin et al 2002). However, it might be that hygienic bees that uncap and remove mites have a specific internal threshold (Theraulaz et al 1998) for performing that task and under low infestation levels only a minority, those with a low threshold for the odorant cue performs the task.…”

“…It is a heritable and highly variable trait which has been used in programs to breed strain of honey bees of European origin, resulting in diverse honey bee populations that are desirable for bee keeping (Guerra Jr. et al 2000;Vandame et al 2002;Ibrahim and Spivak 2006;Harris 2007). Hygienic bees remove affected brood most likely by detecting odor cues emanating from infested hosts, when these cues exceed the response threshold of the bees within the colony (Masterman et al 2001;Martin et al 2002). Indeed, the transcriptional response in antennal-specific genes suggests a key role for chemical discrimination of mite infested cells (Mondet et al 2015).…”

The Ancient Chemistry of Avoiding Risks of Predation and Disease

“…Detection of oleic and linoleic acids and oleic acid ester were enhanced in ''mite-resistant bees'' (Martin et al 2002). Bees avoid flowers where conspecifics may have been killed (Dukas 2001;Abbott 2006) or those treated with extracts of conspecific body parts (Stout et al 1998).…”