THE ABILITY OF COTTON LEAFWORM, Spodoptera littoralis (BOISD.) FIELD STRAIN TO DEVELOP RESISTANCE TOWARD SOME CONVENTIONAL AND BIO-INSECTICIDES

Abstract

This study aim to investigate the development of resistance in cotton leaf worm (CLW) to spinosad and abamectin comparing with the development of resistance toward cypermethrin and methomyl as conventional insecticides. All tested strains were selected by dipping the whole 4th instar larvae. Spinosad was only the compound which tested by feeding method in addition to the dipping technique. The spinosad feeding resistant strain (SFRS) was built up by supplying the 4th instar larve of S. littoralis (Boisduval) with castor leaves treated with spinosad for 23 successive generations continuously in the laboratory. Using dipping technique, spinosad, abamectin, cypermethrin and methomyl resistant strains ( SDRS, ADRS, CDRS and MDRS; respectively ) were selected by exposing the 4th instar larvae for 25 generations to each of spinosad and abamectin; and for 32 generations to each of cypermethrin and methomyl. Results indicated that the ability of the field strain of CLW to develop resistance toward spinosad by the two tested techniques were very high. Resistance ratio (RR) values for SDRS and SFRS were 108 and 87 fold, respectively. The ability of building up resistance toward abamectin and methomyl were almost like each other and not as high as spinosad ( only 19 fold ). Developing resistance toward cypermethrin was quiet higher than abamectin and methomyl ( 31 fold ) but still not as high as spinosad.