Barometric pressure decrease induces density-dependent changes in foraging behaviour in a parasitoid fly

Abstract

Insect activities are known to depend on the environmental conditions. In particular, abiotic factors like rain, temperature and barometric pressure represents risks for such small-sized animals. We previously showed a correlation between changes in barometric pressure and the host-seeking behaviour in larvae of the dipteran parasitoid Mallophora ruficauda. In the present study, using olfactometry, we aimed to understand how intraspecific competition modulated this behaviour in response to several scenarios of pressure drops. On the one hand, we found that in larvae raised at low density of population (i.e. under low intraspecific competition), motivation to search for hosts was affected by either a direct or a progressive decrease of pressure. This observation could be explained by an ability of selective larvae to perceive changes in barometric pressure and adopt avoidance strategies that maintain their probabilities of survival. On the other hand, the ability of motivated larvae to orient to hosts was affected by an abrupt and direct decrease of pressure, independently of the level of intraspecific competition. This was not observed under scenarios where the decrease of pressure was reduced, suggesting that the steepness of pressure drop could lead to a failure in recognition of host chemical cues rather than a behavioral strategy. Together, these results confirmed that barometric pressure impacts host-seeking behaviour in parasitoid larvae, and showed that these effects are modulated by intraspecific competition. In conclusion, this study paves the way to a better understanding of the changes in insect crucial behaviours induced by weather, and provides with more knowledge about the risk factors likely to affect insect survival in a context of pest control.