How Crucial is the Functional Pit Organ for the Varroa Mite?

Abstract

Olfaction as well as gustation, are essential for animal survival, allowing behavioral modulation according to environmental input. We focused our study on an obligate ecto-parasitic mite of honey bees, the Varroa destructor Anderson and Trueman (Parasitiformes, Mesostigmata, Varroidae). By mechanically blocking the main olfactory organ on Varroa forelegs by varnishing with nail polish, we were able to show that other sensory organs cannot significantly compensate chemosensory abilities required for mite’s host selection, identification as well as reproduction. In fact, we found that mites with blocked forelegs had a significantly lower ability to reach a host bee than those with varnished idiosoma and unvarnished control. Furthermore, fewer foreleg blocked mites were feeding on the nurse bees and their reproduction in the brood cells was significantly impaired. The inhibition of reproduction was also reflected in altered expression levels of vitellogenin and vitellogenin receptor genes in foreleg-blocked mites.

Towards disrupting Varroa –honey bee chemosensing: A focus on a Niemann‐Pick type C2 transcript

“…In any case, these findings further support the major role of the foreleg in host detection and recognition by the mite, when compared to the gnathosoma, as demonstrated recently by Nganso et al . (2020). We further focused on the putative role of a foreleg‐specific and the most prominent lipid carrier transcript ( Vd40090 ) in Varroa 's host chemosensing using RNAi.…”

“…Of note, both genes play a critical role in the process of egg development in arthropods (Sappington and Raikhel, 1998; Ali et al ., 2017), and their expression is known to be regulated by exposure to the host of specific stage in the reproductive stage of the mite (Cabrera Cordon et al ., 2013). The low reproductive rate of Vd40090 ‐silenced mites at the reproductive stage is thus not surprizing, as it appears similar to the case when forelegs' ability to sense the host was mechanically blocked by nail polish (Nganso et al ., 2020). Although an indirect effect of Vd40090 silencing on Vg and VgR expressions cannot be rule out at the moment.…”

“…A number of volatile compounds from both the bee larvae and the brood cell have also been demonstrated to guide the invasion of the suitable brood cells by the mites, while cues coming from appropriate aged bee larvae regulate mite reproduction (revied by Soroker et al ., 2019). We have recently shown that although Varroa mite probably contain some sensillae on the gnathosoma (mouthparts), the main chemosensory sensillae of the mite are those on the forelegs (Nganso et al ., 2020). Other chemosensory organs, if they exist eg.…”

The effects of crude propolis, its volatiles and ethanolic extracts on the ecto-parasitic mite, Varroa destructor and health of the African savannah honey bee, Apis mellifera scutellata

“…In general, Varroa mites may be unintentionally exposed to propolis volatiles inside the honey bee colonies but it still remains unclear if they can actually get in direct contact with crude propolis. It is important to note that these mites are mostly found on a bee: a forager bee, which carries them from one hive to another, or a nurse bee which carries them within a brood cell to reproduction, though they can sometimes move for a brief period on the surface of the comb (Nganso et al ., 2020). Thus, it seems very likely that Varroa mites, unlike other external invaders, e.g.…”

“…During each experimental period, the total amount of worker brood per colony was determined as described by Nganso et al . (2020) while the mite-infestation level on approximately 100 worker adult honeybees in each colony was determined as previously described by Nganso et al . (2017).…”