Toxicity of field-weathered insecticide residues to Anaphes iole (Hymenoptera: Mymaridae), an egg parasitoid of Lygus lineolaris (Heteroptera: Miridae), and implications for inundative biological control in cotton

Anaphes iole Girault is an egg parasitoid that has potential as an inundative biological control agent for the tarnished plant bug Lygus lineolaris (Palisot de Beauvois) in cotton in the midsouth USA. Our research addressed survival of A. iole wasps exposed to field-weathered residues of insecticides important to cotton production in the region. Our objectives were to identify insecticides with decay profiles that might be compatible with augmentative releases of A. iole in cotton. Survival of female wasps exposed to field-weathered residues on cotton leaves was determined at 0, 2, 4, 8, 16, 23, and 30 days after treatment with field rates of nine compounds. Immediately after treatment, residues of most insecticides (acephate, cyfluthrin, λ-cyhalothrin, imidacloprid, thiamethoxam, spinosad, fipronil, and oxamyl) resulted in <3% survival. Indoxacarb was the exception with about 30% survival at this time. Survival of wasps exposed to oxamyl, imidacloprid, indoxacarb, and acephate increased considerably during the first week after treatment. Upper limits of 95% CI values for ST₅₀ estimates (days for 50% survival) were ⩽5 days for these insecticides. Survivorship of wasps exposed to λ-cyhalothrin and thiamethoxam was intermediate (95% CI values between 5 and 11 days). Of the insecticides tested, residues of cyfluthrin, fipronil, and spinosad were most deleterious to A. iole (95% CI values > 11 days). Precipitation and wind speed during the study period were less than 30-year averages; thus, under typical weather conditions insecticides might decay more rapidly than observed in this study. Our results suggest that while most insecticides tested exhibited high acute toxicity to A. iole wasps, residues of several compounds decayed rapidly enough to show promise in an augmentative release program.