Deposits of deltamethrin suspension concentrate (s.c.) on Terylene net and cotton cloth were bioassayed in Zimbabwe by exposing them to fed, female Glossina pallidipes Austen, using a 45 s contact with cloth and a brief collision with net. On textured yarn net, the effective life of deposits produced from immersion in 0.1% deltamethrin was longer than on flat yarn net, apparently because the textured net held more insecticide and the insecticide was lost more slowly. The addition of an absorber for ultra-violet light (0.1% 2-hydroxy-4-methoxybenzophenone-5-sulphonic acid) did not significantly extend the effective life of deltamethrin deposits on cloth or net. Applying deltamethrin s.c. as a 0.6% suspension to cotton cloth produced mortalities of <90% for 300 days. Applications of 0.8% deltamethrin on cotton cloth and textured net produced mortalities of <70% for 12–16 months and 9 months, respectively, compared to 4–10 months and 5–7 months, respectively for applications of 0.1% deltamethrin. Chemical analyses indicated that the longer effective life of the 0.6–0.8% was due to a higher initial amount of insecticide and a lower rate of loss. It is suggested that for controlling tsetse in southern Africa, all-cloth targets sprayed with 0.6% deltamethrin s.c. will have an effective life of ca. one year.
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