Low parasite loads accompany the invading population of the bumblebee, Bombus terrestris in Tasmania

Abstract

In its native Europe, the bumblebee, Bombus terrestris (L.) has co-evolved with a large array of parasites whose numbers are negatively linked to the genetic diversity of the colony. In Tasmania B. terrestris was first detected in 1992 and has since spread over much of the state. In order to understand the bees invasive success and as part of a wider study into the genetic diversity of bumblebees across Tasmania, we screened bees for co-invasions of ectoparasitic and endoparasitic mites, nematodes and micro-organisms, and searched their nests for brood parasites. The only bee parasite detected was the relatively benign acarid mite Kuzinia laevis (Dujardin) whose numbers per bee did not vary according to region. Nests supported no brood parasites, but did contain the pollen-feeding life stages of K. laevis. Upon summer-autumn collected drones and queens, mites were present on over 80% of bees, averaged ca. 350-400 per bee and were more abundant on younger bees. Nest searching spring queens had similar mite numbers to those collected in summer-autumn but mite numbers dropped significantly once spring queens began foraging for pollen. The average number of mites per queen bee was over 30 fold greater than that reported in Europe. Mite incidence and mite numbers were significantly lower on worker bees than drones or queens, being present on just 51% of bees and averaging 38 mites per bee. Our reported incidence of worker bee parasitism by this mite is 5-50 times higher than reported in Europe. That only one parasite species co-invaded Tasmania supports the notion that a small number of queens founded the Tasmanian population. However, it is clearly evident that both the bee in the absence of parasites, and the mite have been extraordinarily successful invaders.

Genetic diversity, parasite prevalence and immunity in wild bumblebees

“…This field-based study using wild bumblebee populations supports previous laboratory and experimental work that found genetic heterogeneity within colonies to be negatively correlated with parasitic infections in social insects [32,41,42]. Additionally, high loads of the ectoparasitic mite have been found on the invasive Bombus terrestris in Tasmania, which is inbred owing to small numbers of founding queens [43]. There are two mechanisms that might result in low heterozygosity causing increased parasite prevalence.…”

Invasion success of the bumblebee, Bombus terrestris, despite a drastic genetic bottleneck

“…The successful invasion of Tasmania by B. terrestris (Hingston et al, 2002; Hergstrom et al, 2005) could have been greatly facilitated by the loss of parasites in the process (Allen et al, 2007), as well as by the generalized diet of the species that allowed utilizing introduced and native flowering plants alike (Hingston and McQuillan, 1998;Hingston et al, 2002;Hingston, 2006). Yet a remarkable characteristic of the Tasmanian population is the impoverished allelic richness as compared to New Zealand or Europe (Table 1) (Estoup et al, 1996;Widmer et al, 1998).…”

“…It may be those high-quality families whose offspring are able to invade a new area even with a small founder population. Furthermore, the invading population in Tasmania seems to have left its parasites behind (Allen et al, 2007), among other things, it lacks the trypanosome Crithidia bombi, which drastically lowers the success of founding queens in spring (Brown et al, 2003) and which is known to occur in New Zealand .…”

Traits related to biological invasion: A note on the applicability of risk assessment tools across taxa

“…Natural enemies present Presence of predators Presence of predators decreases invasive insect abundance and increases native insect development rate (Juliano et al 2010); Dispersal increases as presence of parasitoids in native range increases (Paynter and Bellgard 2011); Absence of predators/parasitoids increases the likelihood of establishment (Lawton et al 1986, Tsusui and Suarez 2003, Yan et al 2005, Snyder and Evans 2006, Suarez et al 2008, Ugelvig and Cremer 2012 A, C, E Rate of parasitism Invasive insects parasitized less often than natives (Cervo et al 2000, Gamboa et al 2002, Gamboa et al 2004, Allen et al 2007, Cremer et al 2008, Gray et al 2008, Orledge et al 2010, Comont et al 2014 Certain mutualistic interactions will enhance invasion success (Wilder et al 2011); Presence of suitable host species increases invasion success (Brooks et al 2012…”