Diflubenzuron Did Not Affect the Abilities of the Backswimmer Buenoa tarsalis to Survive and Prey Upon Larvae of Aedes aegypti

TL;DR

This study shows that the insecticide diflubenzuron does not harm aquatic predators like backswimmers or guppies, even at high concentrations, and does not affect their ability to prey on mosquito larvae.

Contribution

The study demonstrates that diflubenzuron is safe for non-target aquatic predators, even at high concentrations.

Findings

Diflubenzuron at recommended field doses did not affect the survival of non-target aquatic predators.

Exposure to 1000-fold field doses did not impair the predation ability of Buenoa tarsalis on Aedes aegypti larvae.

Diflubenzuron poses negligible ecological risks to mosquito predators in aquatic ecosystems.

Abstract

Diflubenzuron is a widely used insecticide. It is used on a variety of target organisms, including mosquitoes’ larvae. However, the misuse of diflubenzuron near and in aquatic environments can lead to unintended effects to beneficial organisms that inhabit these places. Here, we evaluated the impacts of diflubenzuron on two species of water bugs, Buenoa tarsalis and Belostoma anurum, and on the guppy fish Poecilia reticulata. Exposure to the insecticide at concentrations equivalent to the recommended field dose had no impact on the survival of the species. Even at 1000-fold higher concentrations, diflubenzuron was unable to impact on the ability of Bu. tarsalis to prey upon larvae of the mosquitoes Aedes aegypti. The results reinforce the safety of diflubenzuron for non-target aquatic organisms capable of preying on mosquitoes’ larvae.

Diflubenzuron is a growth regulator insecticide and acaricide commonly used to control the immature stages of agricultural pests and mosquitoes that vector relevant animal diseases. Despite the beneficial effects of diflubenzuron, residues of these molecules can reach the aquatic ecosystems, which may lead to detrimental effects on aquatic non-target organisms. Here, we evaluated whether exposures to diflubenzuron (0.267 mg active ingredient [a.i.]/L, which is the equivalent to field dose recommendation) would affect the survival abilities of three non-target aquatic predators: adults of the backswimmer Buenoa tarsalis (Hemiptera: Notonectidae), nymphs of the water bug Belostoma anurum (Hemiptera: Belostomatidae), and adults of the guppy fish Poecilia reticulata (Cyprinodontiformes: Poeciliidae). We further evaluated potential undesired sublethal effects by assessing the abilities of Bu. tarsalis to prey upon second instar larvae (L2) of Aedes aegypti (Diptera: Culicidae) when exposed to the no-observed-lethal concentration (NOLC, 267 mg active ingredient [a.i.]/L., which corresponded to 1000-fold the field dose recommendation). Backswimmer adults were exposed to two sublethal exposure (24 h and 96 h) conditions and three prey densities (i.e., three, six, and nine larvae/100 mL) using artificial water reservoirs. Our results revealed that diflubenzuron (0.267 mg [a.i.]/L) was not lethal to any non-target aquatic predators. Furthermore, exposure (24 h and 96 h) to diflubenzuron at concentrations of 267 mg [a.i.]/L was unable to disturb the ability of Bu. tarsalis to survive and to prey upon Ae. aegypti larvae at all prey densities. Altogether, our findings demonstrate that diflubenzuron exhibits negligible ecological risks to naturally occurring mosquito predators and represents a safe tool to be utilized in aquatic ecosystems.

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