Toxicological responses of the boll weevil (Coleoptera : Curculionidae) ectoparasitoid Catolaccus grandis (Hymenoptera : Pteromalidae) to selected insecticides

A glass vial bioassay was used to determine the toxicity of 10 insecticides to 3 strains of the boil weevil, Anthonomus grandis grandis Boheman, ectop arasitoid Catolaccus grandis (Burks). Technical-grade samples of dimethoate , endosulfan, oxamyl, acephate, malathion, azinphos-methyl, cyfluthrin, met hyl parathion, spinosad, and fipronil were used in bioassays. Three strains of C. grandis were tested: 2 in vivo-reared strains, (i.e., the In Vivo st rain and the Sinaloa strain), and 1 in vitro-reared strain reared on an art ificial diet completely devoid of insect components (i.e., the In Vitro str ain). Endosulfan, spinosad, and azinphos-methyl were significantly less tox ic to the In Vivo strain than other treatments. Endosulfan was also signifi cantly less toxic to the Sinaloa strain than other treatments. Azinphos-met hyl was significantly less toxic to the In Vitro strain than other treatmen ts. In addition, malathion, the insecticide most widely used in bell weevil eradication, was significantly more toxic to the In Vitro strain than othe r treatments. However, it cannot be determined directly from the data which insecticides may be more toxic to C. grandis in the field. Bioassays must be refined so that risks to natural enemies can be predicted reliably. In s o doing, chemical insecticides may be developed and used that may be select ive (i.e., more toxic to a pest than to a beneficial species). The data rep orted herein, however, is likely to be useful to many ecotoxicologists.