Toxicity evaluation of certain insecticides against the red palm weevil, Rhynchophorus ferrugineus (Olivier), under laboratory conditions

Field strain adults of the red palm weevil (RPW), Rhynchophorus ferrugineus, were collected from Al-Hassa, Eastern Province, Saudi Arabia. Four different insecticides; three of which synthetic insecticides viz. beta-cyfluthrin, deltamethrin, and acephate, and one bio-insecticde, matrine were evaluated against egg, larva and adult (male & female) stages of R. ferrugineus (Olivier) under laboratory conditions. These stages were exposed to residual film on transparent plastic cups of each insecticide using Potter precision laboratory spray tower device. Percent mortality of males and females was recorded after exposure time of 0.5, 2.0 and 24 hrs. After exposing the males and females for 2 hrs to 100 and 300 ppm, deltamethrin caused 33.3% and 86.7% morality against males with LC₅₀ 136.5 ppm and 20% and 93.3% against females with LC50 value of 164.23 ppm. Whereas, beta-cyfluthrin caused 46.7% and 86.7% mortality against males with LC₅₀ value of 135.74 ppm and 46.7% and 93.3% against females with LC₅₀ value of 109.4 ppm when exposed for 2hrs to the same concentrations. However, after 24 hrs both insecticides dramatically affected males and females by causing 100% mortality at 400 ppm. Both insecticides at 120 ppm exhibited strong effect against egg stage by causing 100% and 80% unhatchability for beta-cyfulthrin and deltamethrin, respectively, after 96 hrs exposure time. Whereas at 200 ppm both insecticides were highly effective against larva, it caused percent mortality 86.7% and 100 with LC₅₀ value of 93.19 ppm and 87.2 ppm for beta-cyfulthrin and deltamethrin, respectively. In addition, organophosphate insecticide, acephate and bio-insecticide, matrine had no mortality effects against adults up to 500 ppm and 3000 ppm respectively. In conclusion, values of LC₅₀ revealed that the pyrethroids were most effective on male, female, larva and egg stages after 24 hrs when compared with the other compounds.