Behavioural responses of fourth instar Aedes aegypti (Diptera: Culicidae) larvae to Plagiorchis elegans cercariae

Exposure of fourth instar Aedes aegypti larvae to graded concentrations of the entomopathogenic cercariae of the digenean Plagiorchis elegans, induced fundamental changes in the partitioning of time among a number of major behavioural activities. In the absence of the parasite, swimming, breathing and feeding remained stable over time. Grooming was rarely observed. In the presence of cercariae, larvae increased grooming 26-fold. Concomitantly, feeding was reduced to 33% of control values. Times spent swimming and breathing remained unchanged. The increase in grooming activity was attributable to the attachment of cercariae to the surface of the mosquito larvae, but was independent of infection. Grooming reduced cercarial penetration. Seventy-five percent of cercariae were lost to predation by larvae, but their caloric value was insignificant and failed to compensate for the loss of feeding time due to grooming. The findings are discussed in the context of their impact on larval growth, development and survival.