Male mealworm beetles increase resting metabolic rate under terminal investment.

Harmful parasite infestation can cause energetically costly behavioural and immunological responses, with the potential to reduce host fitness and survival. It has been hypothesized that the energetic costs of infection cause resting metabolic rate (RMR) to increase. Furthermore, under terminal investment theory, individuals exposed to pathogens should allocate resources to current reproduction when life expectancy is reduced, instead of concentrating resources on an immune defence. In this study, we activated the immune system of Tenebrio molitor males via insertion of nylon monofilament, conducted female preference tests to estimate attractiveness of male odours and assessed RMR and mortality. We found that attractiveness of males coincided with significant down-regulation of their encapsulation response against a parasite-like intruder. Activation of the immune system increased RMR only in males with heightened odour attractiveness and that later suffered higher mortality rates. The results suggest a link between high RMR and mortality and support terminal investment theory in T. molitor.

Gas exchange patterns of bumble bee foragers before and after exposing to lowered temperature.

The gas exchange patterns are known to vary between insect species, individuals and even intra-individually. Using volumetric-manometric and flow-through respirometry combined with IR-actography we studied how periods of low temperature affect the respiratory patterns of bumble bee Bombus terrestris foragers. We have shown, in this study, that there is a change in the respiratory patterns of individual B. terrestris foragers after exposing to low temperatures. The bumble bees seemed to become more inactive. The different respiratory patterns appeared in succession and the transition from one pattern to another was associated with the change from an active to a resting state. Typical patterns after exposition to low temperature were discontinuous gas exchange cycles (DGCs).