Cattle dung in aquatic habitats alters mosquito predatory biocontrol dynamics

Abstract

Anthropogenic land use changes influence ecosystem functioning and may alter trophic interactions. Intensification of free–range pastoral farming could promote degradation of aquatic habitats, with nutrient inputs adversely affecting water quality and resident communities. Reductions in natural enemies (and potentially efficacy thereof) and dampening of their interaction strength could promote the proliferation of vector mosquitoes, with consequences for disease transmission and nuisance biting. This study examined implications of a cattle dung eutrophication gradient (T0–T4: 0 g L−1, 1 g L−1, 2 g L−1, 4 g L−1 and 8 g L−1) on aquatic habitats for trophic and non–trophic interactions by two larval mosquito (Culex pipiens) natural enemies (notonectid: Anisops sardea; copepod: Lovenula falcifera) using comparative functional responses. Copepods generally exhibited lower interaction strength compared to notonectids, both as individuals and conspecific pairs. Effects of dung pollutants differed among predator groups, with high concentrations dampening interaction strengths being observed for single/paired copepods and paired notonectids, but not single notonectids or heterospecific pairs. Individual predators exhibited Type II functional responses, with feeding rates largely similar across dung concentrations within species. Non–trophic interactions were predominantly negative (i.e., antagonistic) between conspecific pairs and scaled unimodally with prey density. Dung pollution intensified negative non–trophic interactions in notonectid pairs, whereas heterospecific pairs exhibited positive (i.e., synergistic) non–trophic interactions at the highest dung concentration. Physico–chemical properties indicated that turbidity and pH increased with dung treatment concentrations, whereas conductivity and total dissolved solids both peaked at 1 g L−1 and 2 g L−1. These results improve understanding of mosquito regulation in degraded habitats, indicting effects of agricultural pollutants dampen trophic interaction strengths, depending on the taxon.