Reproductive parameters of female Varroa destructor and the impact of mating in worker brood of Apis mellifera

Abstract

During a reproductive cycle, not all daughter mites of Varroa destructor mate and thus leave the brood cells as virgins. Here, we show that virgin mites are present within both the phoretic (10%) and reproductive (8%) mite population. Most (n = 29 of n = 33) of these encountered virgins laid unfertilized (= male) eggs, and some (n = 10) mated later on with their own son. These findings were verified by tests with artificially reared virgin mites. Obviously, mating is not a prerequisite for Varroa reproduction. However, due to the small number of reproductive cycles, the contribution of virgins to the Varroa population is regarded as low. This study also confirms conclusively that sex of V. destructor is determined via arrhenotokous parthenogenesis and not-as previously assumed-via pseudo-arrhenotoky. Furthermore, reproductive parameters of naturally invaded and artificially introduced Varroa females were compared, and artificial infestation was reconfirmed as a suitable method.

Varroa destructor: how does it harm Apis mellifera honey bees and what can be done about it?

“…Recently, Häußermann et al revealed the possibility of a virgin mite beginning the phoretic phase. In that case, the mite invades a brood cell, lays an unfertilised egg in a new comb, and mates with its male offspring [13]. This finding confirms that female Varroa do not need to mate to lay eggs, and thus, have an arrhenotokous parthenogenetic reproduction system.…”

Genome-Wide Identification of Long Non-coding RNAs in the Gravid Ectoparasite Varroa destructor

“…Considering these timing, we collected the mites 48 h later after the mite was introduced into the freshly capped cells. The artificial infestation has been established to be a suitable method for V. destructor research (Dietemann et al, 2013;Lin et al, 2018;Häußermann et al, 2019), and mites parasitized in the capped brood cells are less variable in physiology and fitness than on the adult bee bodies (Milani, 1995). The mites collected were further confirmed gravid with dilated post-abdomen, from which we can even see the eggs inside under microscope (Supplementary Figure 1B).…”

“…destructor lives entirely on its host and cannot survive independently (Traynor et al, 2020) with two life cycles: the phoretic (non-reproductive) phase on the body surface of adult bees and the reproductive phase in the sealed brood cells with immature bees (Martin, 1994). Reproduction of the parasite starts from the oogenesis process, which occurs since approximately 6 h later after the invaded cell is capped and is crucial for understanding the reproductive biology of the parasite (Garrido et al, 2000;Häußermann et al, 2019). A great number of studies have been performed on different life phases of this obligate bee parasite, however, molecular studies are very limited as a result of the lack of genomic information.…”

Three Decades of Selecting Honey Bees that Survive Infestations by the Parasitic Mite <em>Varroa destructor</em>: Outcomes, Limitations and Strategy

“…Indeed, a cross-fostering experiment involving queens exchanged between colonies with either high or low mite reproduction rates revealed that the SMR values changed according to the origin of the new queen (Harris and Harbo, 2000). However, SMR also depends on many honey bee-or miterelated factors: it is influenced by the reproductive ability of the mite entering the cell (Bienefeld et al, 1998;Fuchs, 1994;Harris and Harbo, 1999;Häußermann et al, 2019;Locke et al, 2012), by the origin of the brood (Conlon et al, 2018;Frey, 2009), by the brood quantities available (Locke and Fries, 2011) and by the behaviour of adult workers, including VSH (see section 1.1.1.2) (de Guzman et al, 2008;de Guzman et al, 2015;Harris et al, 2010;Harris et al, 2012;Kirrane et al, 2015;Kirrane et al, 2011;Kirrane et al, 2018) and uncapping-recapping behaviour (Oddie et al, 2018a) targeting infested cells. SMR has also been shown to fluctuate according to the parasitic pressure: at higher infestation levels, the number of offspring per mite tends to decrease (Eguaras et al, 1994), which may negatively impact the repeatability of trait measurement.…”