Department of Entomology

Title: "Pathogen of most resistance: Floral chemicals, temperature and the bumblebee Trypanosomatid Crithidia bombi." 

Abstract:

Nectar and pollen are rich in phytochemicals, some of which can reduce disease in pollinators. These effects could influence ecological and evolutionary relationships between plants, pollinators, and parasites that cause pollinator disease. I used cell cultures of the intestinal trypanosomatid parasite of bumble bees, Crithidia bombi, to

(1) describe how resistance to nine floral phytochemicals varied among four parasite strains,

(2) evaluate effects of phytochemical combinations on parasite growth, and

(3) test for evolution of resistance to individual phytochemicals and a two-compound blend.

Results

Crithidia bombi showed resistance to several phenolics at levels beyond those found in nectar and pollen; literature surveys showed that C. bombi resistance to these compounds exceeded that of bloodstream-form trypanosomatids by several orders of magnitude. However, thymol and eugenol inhibited growth at concentrations found in pollen and nectar. C. bombi strains varied in resistance to phytochemicals, which could mediate inter-strain competition in wild populations. Thymol and eugenol had synergistic effects against parasite growth that varied in magnitude across parasite strains. Synergistic antiparasitic effects of phytochemicals may be an unexpected benefit of floral diversity for pollinators. Crithidia bombi evolved increased resistance when chronically exposed to single chemicals or the 2-compound blend. Patterns of phytochemical exposure in monotonous landscapes could attenuate the medicinal value of phytochemicals. Plant communities could select for parasite strains with resistance to locally common floral phytochemicals and blends, thereby shaping the spatial and genetic structures of parasite populations. Overall, exposure to phytochemicals, whether within bees or during parasite transmission via flowers, could influence infection dynamics and host-parasite ecology.

Outlook

At UCR, I am studying how temperature affects interactions between bumble bees, C. bombi, and the core gut microbiota. Elevated body temperatures can ameliorate infection in many taxa. However, effects of elevated temperature on bumble bee infection remain uninvestigated. Moreover, no studies have examined the consequences of elevated body temperature for core symbionts of infected hosts. High temperatures could mediate competition between parasites and symbionts in the gut, with consequences for host infection and fitness. I will compare thermal tolerance of parasite and symbiont cell cultures, test how temperature affects parasite-symbiont competition in vitro, and document how temperature affects bumble bee infection and gut microbiota. Results may reveal novel microbiome-mediated costs and benefits of febrile states in animals.