Evaluation of insecticide dips as protectants of stored dried fish from dermestid beetle infestation

Dried Tilapia species were dipped for 4 s in 10 l. of solutions containing, at two concentrations, pirimiphos-methyl, iodofenphos, fenitrothion, diflubenzuron or deltamethrin. After draining excess fluid, the fish were left in a store at Lake Turkana, Northern Kenya, where they were subjected to infestation by Dermestes maculatus Degeer (Coleoptera: Dermestidae). The treatments were compared with untreated or water dipped controls and to fish dipped in a commercial formulation of pyrethrins synergised with piperonyl butoxide. All treatments gave good protection for 2 months but only the deltamethrin gave adequate control for 6 months. Deltamethrin had a distinct repellent effect which was lacking with other treatments except the natural pyrethrins. There was no difference in effectiveness between high and low dosages nor between different formulations. Low dosages of each treatment produced residues in fish that were similar to the maximum recommended for raw cereals and pulses and can be regarded as levels that would be safe for human consumption. The results suggest that deltamethrin and pirimiphos-methyl have potential for use as long lasting protectants of dried fish in store.