Lethal and non-lethal effects of predators on Culex mosquitoes

Background/Question/Methods

The study of interactions among medically important mosquitoes and their predators has the potential to offer insight into patterns of population and disease outbreaks. The effects of predators on mosquitoes can be particularly complex: predators impact mosquitoes both by killing them, and by inciting predator-avoidance behaviors that carry energetic costs for those mosquitoes that avoid being killed.   When defensive traits are costly for the vector, predators may then have cascading non-lethal effects on pathogen prevalence if the traits altered affect vector abundance or competence.  Here, we investigate the effects of a dragonfly nymph predator, Erythemis simplicicollis, on varying densities of larval nothern house mosquitoes (Culex pipiens sp.).  First in laboratory microcosms and later in the field, we examined both mosquito survivorship and whether any non-lethal effects of predator exposure carry over to affect the size and longevity of adult mosquitoes.  Survivorship from the larval to adult stage was measured along with wing length and longevity of adults.

Results/Conclusions

We found, at most densities, dragonfly nymphs were successful in reducing survivorship of mosquito larvae as well as reducing wing length compared with no-predator controls.  These data suggest larval predators can ultimately help regulate adult mosquito populations, both by reducing overall densities of mosquito adults and by reducing the robustness of those mosquitoes that evade predation. Ongoing field studies are examining how predator community structure impacts mosquitoes through both lethal and non-lethal channels.  Finally, field surveys of predator communities across disturbance gradients will put these results into a landscape perspective and may help explain geographic patterns in disease outbreaks.