Toxicity of imidacloprid, fenpropathrin, and dimethoate to Ceraeochrysa cubana (Neuroptera: Chrysopidae) through different exposure routes

Abstract

Ceraeochrysa cubana (Hagen) (Neuroptera: Chrysopidae) is an important predator with potential use to control various agricultural pests, including Diaphorina citri Kuwayama (Hemiptera: Liviidae). However, the indiscriminate use of insecticides may affect the performance of this lacewing, reducing its efficiency as a natural enemy. The goal of this study was to evaluate the lethal effect of imidacloprid, fenpropathrin, and dimethoate on C. cubana using different routes of exposure. Bioassays of topical, residual, ingestion, and residual + ingestion (simultaneous exposure) of the active ingredients on the lacewings were performed. The tolerance ratio (TR) was calculated from the lowest LC50 observed. In addition to the lethal effect, we also studied the repellent effect of imidacloprid and fenpropathrin on first instar larva of C. cubana when Ephestia kuehniella Zeller (Lepidoptera, Pyralidae) eggs were treated with those insecticides. In the toxicity bioassay, the residual exposure of dimethoate was the most lethal (lower value of LC50), followed by residual + ingestion exposure of dimethoate and fenpropathrin. With topical exposure, insecticides had similar toxicity and TR was between 20.76 and 23.61-fold. Imidacloprid was not toxic via ingestion and residual exposure; consequently, we did not estimate LC50 in those cases. Ephestia kuehniella eggs treated with imidacloprid did not repel C. cubana larvae while those treated with fenpropathrin had a repellent effect. Dimethoate was toxic to C. cubana and it should be used with caution while imidacloprid has a lower lethal effect via residual and ingestion exposure and it does not have a repellent effect on C. cubana.