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 boll weevil, Anthonomus grandis grandis Boheman, ectoparasitoid Catolaccus grandis (Burks). Technical-grade samples of dimethoate, endosulfan, oxamyl, acephate, malathion, azinphos-methyl, cyfluthrin, methyl 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 strain and the Sinaloa strain), and1 in vitro-reared strain reared on an artificial diet completely devoid of insect components (i.e., the In Vitro strain). Endosulfan, spinosad, and azinphos-methyl were significantly less toxic to the In Vivo strain than other treatments. Endosulfan was also significantly less toxic to the Sinaloa strain than other treatments. Azinphos-methylwas significantly less toxic to the In Vitro strain than other treatments. In addition, malathion, the insecticide most widely used in boll weevil eradication, was significantly more toxic to the In Vitro strain than other treatments. However, it cannot be determined directly from the data which insecticides may be more toxic to C. grandis inthe field. Bioassays must be refined so that risks to natural enemies can be predicted reliably. In so doing, chemical insecticides may be developed and used that may be selective (i.e., more toxic to a pest than to a beneficial species). The data reported herein, however, is likely to be useful to many ecotoxicologists. [ABSTRACT FROM AUTHOR]