Absorption and Toxicity of Three Radioactive Insecticides in Larvae of Two Species of Mosquitoes

Abstract

Acetone-water suspensions of solutions of radioactive DDT, Bayer 21/199, and Am. Cyanamid 12880 [O,O-dimethyl S- (N-methylcarbamoylmethyl)- phosphorodithioate] were tested against fourth-instar Anopheles quadrimaculatus Say and Aedes taeniorhynchus (Wied.) larvae [Culicidae:Diptera]. Concentrations required for equivalent 24-hour mortality were in the order of DDT < 21/199 < 12880. A. quadrimaculatus were more susceptible to DDT and 12880 but less to 21/199 than taeniorhync hus; however, at the LD-50 only small differences (0.0033- 0.0142 üg/larva) were seen between species and chemicals. Increasing the number of quadrimaculatus larvae per unit volume resulted in lower mortalities with DDT, but no change with 21/199 and 12880. A. quadrimaculatus larvae exposed to 21/199 for 48 hours absorbed a maximum amount in the first few hours but the mortality increased with time. When quadrimaculatus larvae were transferred to clean water, 73% of the acquired dosage of 21/199 was excreted in 12 hours. Live larvae of both species absorbed more 21/199 than did dead larvae.