Parasites are ubiquitous among insects and well-studied, but knowledge of their full range of host effects is not complete, especially concerning their impact on physical performance of hosts. The horned passalus beetle, Odontotaenius disjunctus (Illiger), in the USA is frequently parasitized by Chondronema passali Leidy, a nematode that can number in the thousands within the hemocoel. We performed an experiment that examined the effects of this parasite on a key performance metric, lifting strength, which should be important during fighting. We assessed beetle lifting strength using a vertically-mounted force gauge, as well as their body mass. At the end of the experiment, we dissected the beetles to determine parasite status and gender. The average beetle (1–2 g each) lifted between 300 and 400 g during the trials. Though the final sample size of non-parasitized beetles was small (n = 8), our results showed parasitized beetles tended to lift 17% less weight than non-parasitized beetles, and this effect approached significance ( p = 0.0766). Beetles tended to lift the most during their first trial, which is relevant information for other researchers who employ performance trials. Also of note was that beetles lost 11% of their body mass during the first week of captivity, which may stem from initial stress or the loss of their accumulated frass supply, which they ingest to obtain endosymbiotic gut microbes. Finally, we were surprised to discover that parasitized beetles lost less mass during captivity than did non-parasitized beetles, which is a result that deserves further study.
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Vol. 69 • No. 4