Effect of antifungal agents on biological fitness of Lygus hesperus (Heteroptera: Miridae)

Artificial diets have become important components of rearing systems for insects that are used for research purposes and in commercial production. Because the rearing conditions for insects also provide ideal settings for mold growth, antifungal additives are often used to reduce diet contamination. However, the antifungal agents must not only be effective in mold suppression, they must also be safe to the target insects of the rearing programs. The toxicity of five commonly used antifungal agents (benzoic acid, formalin, methyl paraben, propionic acid, and sorbic acid) was tested using diet bioassays on Lygus hesperus Knight, and the effect on biological fitness was measured. Biological fitness was defined as total number of survivors, mean biomass (dry weight) accumulated per cage over the total treatment period, egg production, time to adult emergence, and time to start of egg laying. Methyl paraben and formalin were found to have significant negative effects on these measurements of biological fitness. Challenge tests to determine the ability of the antifungal agents to suppress mold growth when inoculated into the diet medium are currently in progress.