Differential virulence in a multiple‐host parasite of bumble bees: resolving the paradox of parasite survival?

Abstract

Parasite virulence determines both the impact that parasites have on their hosts and parasite fitness. While most studies of virulence have involved single-species hostÁparasite interactions, the majority of parasites are likely to use multiple concurrent host species. Our understanding of how this impacts on parasite epidemiology and virulence is limited. Using the bumble bee Bombus lucorum, which exists in sympatry with B. terrestris in multi-species assemblages, and their generalist micosporidian parasite Nosema bombi, we tested whether the apparent paradox of parasite maintenance due to parasite virulence in a single host, B. terrestris, could be resolved through understanding the parasite's virulence in this sympatric host species. Nosema bombi significantly impacted colony growth, individual longevity, and individual development in B. lucorum. However, these effects were different both qualitatively and quantitatively to the parasite's impact in B. terrestris. Infected colonies of B. lucorum successfully produced both male and female reproductives, and infected female reproductives were capable of successful mating. Variation in life-history across host species may explain differences in the virulence, or impact of the parasite in B. terrestris and B. lucorum, with species with shorter life-cycles being more likely to transfer the parasite from one annual generation to the next. These results suggest that to understand the virulence and epidemiology of multi-host parasites we need to examine their ecological interactions across their various host species.

Molecular detection of Spiroplasma apis and Spiroplasma melliferum in bees

“…Spores of Nosema bombi from Bombus terrestris were less infective in Bombus lapidarius and Bombus hypnorum, but even genotype-genotype interaction were present, since N. bombi showed different infectivity in different B. terrestris colonies (Schmid-Hempel and Loosli, 1998). Also the virulence of N. bombi was different in B. terrestris and Bombus lucorum, possibly a consequence of the shorter life cycle of B. lucorum (Rutrecht and Brown, 2009). It is evident, to resolve these issues for spiroplasmas, more research is needed, for now we know from feeding experiments in honeybees these bacteria can cause harm in pollinators (Clark, 1978;Mouches et al, 1982).…”

Interspecific geographic distribution and variation of the pathogens Nosema bombi and Crithidia species in United States bumble bee populations

“…and may play key ecological roles in the population dynamics of their hosts, which are among the most important pollinators globally in both agriculturally intense settings (Velthuis and Van Doorn, 2006) and in natural settings where they are cornerstone species in pollination networks (Memmott et al, 2004). Most of these studies have been conducted in Western Europe and have focused on the most common host species, Bombus terrestris L. and Bombus lucorum L. (Shykoff and SchmidHempel, 1991;Korner and Schmid-Hempel, 2005;Rutrecht and Brown, 2009). Little is known about the pathogen complex of the approximately 52 North American Bombus species.…”

“…N. bombi is an obligate intracellular pathogen that produces systemic disease in its host (Fries et al, 2001;Larsson, 2007); the effects are generally chronic, including reduction in individual reproduction rate Schmid-Hempel, 2007, 2008), life span (Fantham and Porter, 1914;Schmid-Hempel and Loosli, 1998;Rutrecht and Brown, 2009) and colony growth (Rutrecht and Brown, 2009). There has been a limited amount of research on susceptibility of European bumble bee species to N. bombi (Schmid-Hempel and Loosli, 1998;Schmid-Hempel, 2007, 2008;Rutrecht and Brown, 2009), and none for American bumble bees. One European study found significant differences in susceptibility of different host species to N. bombi spores harvested from B. terrestris (Schmid-Hempel and Loosli, 1998), but Rutrecht et al (2007) reanalyzed these data and did not find differences.…”

Parasite and host assemblages: embracing the reality will improve our knowledge of parasite transmission and virulence

“…In contrast, the multi-host microsporidian Nosema bombi appears to exhibit runaway virulence in one host species Otti & Schmid-Hempel (2008) and more adaptive virulence in a second (Rutrecht & Brown 2009). This pattern may match predictions based on host resistance Gandon (2004), but the relationship to host quality is unclear.…”