Parasite infection delays ecdysis in an insect model (Rhodnius prolixus), with ecdysis-related defects and mortality

Insect development depends on the success of moulting, which is the process of producing a new cuticle and shedding the old one. While there is evidence that insects infected by parasites can experience increased mortality during moulting, this phenomenon is not well quantified or understood. Here we used the triatomine bug Rhodnius prolixus (Hemiptera: Reduviidae) and the protozoan parasite Trypanosoma rangeli as a model system to address this. Rhodnius prolixus has long been used as a model for moulting due to its easy maintenance and predictable development after feeding. Here, insects were first infected through feeding on infected mice, followed by haemocoel injection of the parasite. Survival and moulting-related behaviour were then assessed. Mortality of 4th instar T. rangeli-infected nymphs was 6 % higher than that of uninfected insects. Infected insects showed more defective moults as well as failure to moult. Moulting was initiated at 42 days after the blood meal in infected insects, a severe delay compared to 17 days in uninfected insects. We also analyzed ecdysis-related behaviour of insects under infection. Infected insects took longer to complete the actual process of ecdysis (once initiated) than did uninfected insects, specifically at the beginning (ecdysial line disruption) and the end (exuvium release) of the process. Our results indicate likely effects of infection on the behaviours that allow the insect to escape from the old cuticle, and help understand fundamental physiological processes of insect development under infection. Increased mortality during moulting of infected insects is probably a common phenomenon, but one that is likely largely overlooked in both laboratory and field studies.