Elusive enemies: consumptive and ovipositional effects on mosquitoes by predatory midge larvae are enhanced in dyed environments

Mosquito-borne disease incidences continue to proliferate and cause enormous mortality and debilitation rates. Predatory natural enemies can be effective in population management strategies targeting medically-important mosquito species. However, context-dependencies and target organism behavioural responses can impede or facilitate biological control agents. Black pond dye has been shown to be a strong mosquito oviposition attractant, and could potentially be used alongside predatory agents to create mosquito population sink effects. Here, we thus examine the predatory impact of larvae of the non-biting chaoborid midge Chaoborus flavicans towards larvae of the West Nile virus vector mosquito complex Culex pipiens in the presence and absence of black pond dye. We then examine the ovipositional responses of C. pipiens to predation risk and dye in laboratory-, semi-field- and field-based trials. Larval C. flavicans exhibited potentially population destabilising type II functional responses towards mosquito larvae irrespective of the presence of pond dye. Neither consumption rates nor functional response parameters (attack rates, handling times) were significantly influenced by the presence of dye, indicating a use of hydromechanics to detect mosquito prey by chaoborids. Wild-caught adult C. pipiens did not avoid predatory chaoborids when ovipositing, however they were significantly more attracted to oviposit in dye-treated water regardless of the presence of predators. We thus demonstrate high predatory impact towards mosquito larvae by non-biting chaoborid midges during their predaceous aquatic larval stages, and proliferations of such predators may assist or augment control efforts for mosquitoes. Our results suggest a lack of influence of predatory dipterans on oviposition selectivity by C. pipiens mosquitoes, and that pond dye may enhance the efficacy of select predatory biological control agents through the creation of population sinks, characterised by high rates of oviposition and subsequent predation.