Disturbance in temporary pools: Consequences for community and mosquito dynamics

Background/Question/Methods

There is increasing evidence across many natural systems that high species diversity or community saturation can buffer against invasion or production of unwanted species while community simplification can have the opposite effect. Experimental manipulations of diversity gradients or gradients of other measures of food web complexity for effects on mosquitoes are rare.  However, evidence for potential effects of species richness saturation or community simplification in mosquito breeding sites may be gleaned from disturbance studies. Disturbances, through community structure alteration, may then have residual effects on mosquito oviposition site selection and production. We very briefly survey existing literature for such evidence from various disturbances including desiccation, flash floods, eutrophication gradients, and residual effects of predators, and pesticides.  We also consider two new disturbance experiments in outdoor artificial pools: 1) residual effects of a top predator, Salamandra infraimmaculata, after it has metamorphosed and exited pools; 2) effects of different types of pesticides: no pesticide; Bacillus thuringiensis israelensis (BTI), a narrow-spectrum bacterium; temephos, a broad-spectrum organophosphate; pyriproxifen, an insect growth regulator.  We predicted that larval Salamandra and the broad-spectrum pesticides would cause a trophic cascade (fewer herbivores, more algae) and consequently, their residual effects would be greater mosquito oviposition and larval performance.

Results/Conclusions

Much of the evidence from the literature suggests that disturbances to aquatic communities cause an increase in mosquitoes but there was not consistent support for a diversity-mosquito relationship. As predicted, Salamandra caused a trophic cascade as well as residually causing an increase in oviposition in former Salamandra pools. However, Salamandra appears to create an ecological trap: there was considerably lower larval mosquito survival. Temephos and pyriproxifen caused strong immediate reductions in species diversity, which were not followed by an immediate mosquito resurgence. After pesticide application, mosquito oviposition was initially higher in control pools. However, after some time, oviposition and larval mortality increased dramatically in the pyriproxifen treatment.  Thus in both the Salamandra and pesticide experiments, mosquito oviposition and larval performance were not tightly linked to diversity but both the Salamandra and pyriproxifen residually appear to provide ecological traps, attracting mosquito oviposition but causing high mosquito larval mortality.  Future experiments will assess the mechanism for these results.