Insecticides Alter the Ability of Predator Assemblages to Suppress Prey

Abstract

Agrochemicals are often deposited into freshwater bodies via rainfall and snowmelt events and can have consequences for populations and communities. Insecticides in aquatic systems can cause mortality, behavioral, and reproductive changes in nontarget invertebrates, which have the potential to indirectly effect other populations and ecosystem processes. Thiamethoxam (TMX) is part of the neonicotinoid family, a branch of insecticide that mimics nicotine and binds to the acetylcholine receptor, causing paralysis and death. This research examined 1) the effects of environmentally relevant concentrations of TMX on the diversity, species composition and total abundance of aquatic predatory insects present in freshwater ponds, and 2) how the effects of TMX on each of the diversity, species composition and total abundance of aquatic predatory insects may compromise the ability of the predator assemblage to suppress their prey. I found that, in the absence of TMX, the aquatic predator assemblage present is very effective at suppressing snail population growth. The ability of the predator assemblage to suppress prey, however, is severely reduced in the presence of TMX. TMX reduced the number of predatory insect species present, changed the species composition of the predatory insects present, and reduced the total abundance of predatory insects present. Hemipteran insects appear to be more vulnerable to TMX than Odonates. It appears that a reduction in predator abundance had a minor effect in weakening the ability of the predator assemblage to suppress prey. Furthermore, the effect of species loss, in general, appeared to have little effect on the ability of the predator assemblage to suppress prey. Instead, it appears that the loss of one particular species of predator (Belostoma) as the result of TMX exposure is what mostly likely compromised the ability of the predator assemblage to suppress prey. Given the greater vulnerability of Belostoma to TMX, this means that TMX exposure will likely compromise the ability of the predator assemblage to suppress prey.