Control of two–spotted spider mite <i>Tetranychus urticae</i> Koch (Acari: Tetranychidae) by some selected chemicals

Abstract

The experiment was conducted to study the effectiveness of four commonly used chemicals viz., deltamethrin, cypermethrin, malathion and sulphur against two-spotted spider mite (TSSM), Tetranychus urticae Koch on potted bean plants and on excised leaf discs. Mite population remained significantly lower in all treated plots except malathion treatment. The population of T. urticae differed significantly due to different chemicals and it remained lower up to 4th week on single-sprayed plants, which again increased. But in double-sprayed plants mite population was checked and remained significantly lower. The estimated LC₅₀ values for cypermethrin, malathion, deltamethrin and sulphur were 2.9956, 15.8663, 0.5386 and 20.7045 nl.cm^-2 respectively when the chemicals were sprayed before mite release. But the LC50 values for these chemicals sprayed after mite release were estimated 1.8110, 8.2746, 0.2192 and 6.8308 nl.cm^-2. The use of chemicals is essential for better yield of crops. Among the four tested chemicals the pyrithroids (cypermethrin and deltamethrin) were found more effective against the TSSM than the other two. Key words: Two-spotted spider mite, Tetranychus urticae, bean, deltamethrin, cypermethrin, malathion, sulphur Univ. j. zool. Rajshahi Univ. Vol.25 2006 p.15-18