No abstract

Habitat avoidance is an anti-parasite behaviour exhibited by at-risk hosts that can minimize exposure to parasites. Because environments are often heterogeneous, host decision-making with regards to habitat use may be affected by the presence of parasites and habitat quality simultaneously. In this study we examine how the ovipositing behaviour of a cactiphilic fruit fly, Drosophila nigrospiracula, is affected by the presence of an ectoparasitic mite, Macrocheles subbadius, in conjunction with other environmental factors – specifically the presence or absence of conspecific eggs and host plant tissue. We hypothesized that the trade-off between site quality and parasite avoidance should favour ovipositing at mite-free sites even if it is of inferior quality. We found that although flies avoided mites in homogeneous environments (86% of eggs at mite-free sites), site quality overwhelmed mite avoidance. Both conspecific eggs (65% of eggs at infested sites with other Drosophila eggs) and host plant tissue (78% of eggs at infested sites with cactus) overpowered mite avoidance. Our results elucidate the context-dependent decision-making of hosts in response to the presence of parasites in variable environments, and suggest how the ecology of fear and associated trade-offs may influence the relative investment in anti-parasite behaviour in susceptible hosts.

Host bioenergetics and energy fluxes can be applied to measure the ecological and physiological effects of parasitism. By measuring changes in host metabolic rate, one can estimate the physiological costs of infection. Additionally, metabolic rate dictates the rate of resource conversion within a host and, by extension, the resources available to a parasite. We hypothesize that parasites are selected to respond to cues that indicate high resource availability, that is, host metabolic state. We investigated whether an ectoparasite mite (Macrocheles subbadius) can differentiate between potential hosts (Drosophilia nigrospiracula) on the basis of relative carbon dioxide output as measured by respirometry. In pairwise choice tests, mites were allowed to choose between two size-matched fruit flies with differing metabolic rates or levels of CO output. Our results showed that mites preferentially infect flies with relatively higher respiration rates. Accordingly, we investigated whether fly respiratory rate (measured by CO production) changes in response to injury, potentially explaining a previously reported preference for injured flies. We also tested whether chemical cues released during injury influence preference for injured hosts. We determined that fly exudate (mostly consisting of hemolymph) applied to an uninjured fly released at the site of injury significantly increased the likelihood of infection, but injury did not significantly change the CO output of the flies. Our results suggest that parasites are relying on chemical cues not only for host finding but also to discriminate between hosts on the basis of the rate of respiration, with potentially important implications for the metabolic theory of ecology.

The geographic range and occurrence of tick species is dynamic. This has important public health implications due to important tick species that can transmit pathogens. This study presents a retrospective review of tick genera recovered from humans and submitted for identification in Alberta, Canada, over a 19-year period. The total number of ticks and proportion of genera were analyzed over time. Molecular testing for a number of pathogens associated with Ixodes scapularis and I. pacificus was conducted. A total of 2,358 ticks were submitted between 2000 and 2019, with 98.6% being acquired in Alberta. The number of ticks submitted increased significantly over time ( p < 0.0001). Dermacentor ticks were the most abundant genus, followed by Ixodes and Amblyomma . There was a significant decrease in the proportion of Dermacentor ticks between 2013 and 2019 ( p = 0.02), with a corresponding increase in the proportion of Ixodes ticks over the same time ( p = 0.04). No statistically significant change in seasonality was identified. Borrelia burgdorferi was detected in 8/76 (10.5%; 95% CI 5.4–19.4%) of all I. scapularis and I. pacificus ticks submitted. This translated to a B. burgdorferi positivity of 0.35% (95% CI 0.15–0.68%) among all ticks received. Dermacentor species (especially D. andersoni ) remains the most common tick feeding on humans in Alberta. Small numbers of vector species (including I. scapularis/pacificus ) are encountered annually over widely separated geographic areas in the province. The risk of exposure to tick-borne pathogens (e.g. Lyme disease) in Alberta remains low.