title: Parasitellus fucorum: a beneficial mite for bumblebees
Creators: name: McArthur, Robin
Publisher: name: University of Reading
Year: 2023

description: It is known that bumblebees (Bombus) have a wide variety of different mite (Acari) species associated with them, however research into the nature and effects of these relationships is scarce. For many species our understanding of their biology and life cycles are incomplete, and our understanding of the effects that most bumblebee-associated mites have on their hosts is likewise inadequate. There have been many studies conducted on a small number of bumblebee associated mite species, such as the obligate endoparasite Locustacarus buchneri, but information on the majority of mite species is limited, and much of the information available is outdated due to changes in the ecological context of British bumblebees in the intervening time (the extinction of several species, introduction of a ‘new’ species (Bombus hypnorum), fragmentation of habitats, and potential importation of foreign mites). One species of particular interest is Parasitellus fucorum. P. fucorum is frequently suggested in previous literature to be a potential mutualist with the bumblebees it associates with, based on the hypothesis that the predatory actions of P. fucorum in bumblebee colonies will result in a net benefit to colony fitness, outweighing any negative effects from the kleptoparasitic instars of P. fucorum’s life cycle. However, no empirical testing has previously taken place to evaluate this hypothesis. P. fucorum is a relatively large, highly mobile and predatory mite species. All species within the genus Parasitellus are obligate associates of bumblebees in the Holarctic region, with broadly similar ecology. In order to address this issue, we aimed to determine what effects Parasitellus fucorum association had on bumblebees at the individual or the colony level. To achieve this we tested the ability of P. fucorum to predate various bumblebee pests and parasites including greater wax moth (Galleria mellonella) eggs and bumblebee wax moth (Aphomia sociella) eggs and 1st instar larvae, and found that P. fucorum deutonymphs were capable of predating all three. It was also shown that P. fucorum predates Tyrophagus putrescentiae mites, a fungivorous pest species commonly found within bumblebee colonies. This work represents the first evidence of these predatory relationships. A field trial was conducted to test the impact of P. fucorum inoculums on commercial bumblebee colony development, the results of which showed that the presence of a P. fucorum population within bumblebee colonies leads to a 165% greater colony mass increase, a 12% relative increase in syrup consumption and a 119% higher number of workers on average compared with controls. This is the first empirical evidence of benefits to bumblebee fitness resulting from association with P. fucorum. These experiments required large numbers of P. fucorum mites, so a suitable method for rearing P. fucorum in laboratory conditions was developed. It was also shown during this project that phoretic P. fucorum numbers on spring queens are inversely correlated with the likelihood of the queen being infested by the parasitic nematode Sphaerularia bombi. A survey of phoretic mite groups and trends in their associations with bumblebee queens in Reading was conducted in order to better inform the project with up-to-date information on local mites, which showed that all mites groups except Parasitellus varied significantly in abundance between different bumblebee species, and that the most common local bumblebee associated mites were Kuzinia spp., Scutacarus spp., Pneumolaelaps spp., and Parasitellus fucorum. From the results of this project it has been shown that the presence of Parasitellus fucorum within bumblebee colonies is beneficial to their development, likely due to the predatory activity of P. fucorum within the colony upon bumblebee pests and parasites. Our findings will be useful to pollinator researchers and acarologists, and may be of interest for future efforts in bumblebee conservation.