Impacts of parasites on insect moulting

Insect development occurs through moulting, where the individual generates a new cuticle and sheds the old one, allowing the insect to grow and develop. This process can be impacted by parasites. However, the way different parasites can impact insect moulting is unknown. We first review studies on insect infection and its effect on insect moulting by considering interactions between insects and: (i) protozoans; (ii) fungi; (iii) viruses; and (iv) parasitoids. We show that insect moulting is impacted by moulting delays, non-moult and defects after moulting, besides increasing insect mortality during moulting. However, while there is evidence that parasite- infected insects can experience increased mortality during moulting, this process is not well understood yet. We then documented this so as to raise hypotheses about the mechanisms, with a focus on behaviour, using as a model system the triatomine bug Rhodnius prolixus (Hemiptera: Reduviidae) and the protozoan parasite Trypanosoma rangeli. We quantified mortality and investigated alterations in ecdysis-related behaviour. We found that the high mortality of infected insects is related to increases in the time taken to finish ecdysis. We then investigated cuticular thickness and ecdysone levels as potential factors to explain this phenomenon. Mortality of infected insects was 6% higher than that of uninfected insects. Infected insects show a thinner cuticle over time and lower ecdysone levels compared to controls. We suggest this thin cuticle in infected insects is associated with the moulting delay. As moulting is delayed, we investigate glycogen content in the fat body and intestine morphology as possible factors. Infected insects have low glycogen content in the fat body and intestine morphology is not altered between infected and control insects, but intestine epithelium is apparently thicker in infected than the control. Our results allow us to understand better the effect of insect infections at behavioural, morphological and hormonal levels. This study is a starting point for further reasearch on the moulting physiology of insects infected by parasites in order to improve our understanding of insect-parasite interaction. Keywords: Cuticle. Development. Ecdysis. Ecdysone. Fungus. Moult. Parasitoid. Pathogen. Physiology. Virus.