COMPARATIVE TOXICITY AND MUTAGENICITY OF FOUR INSECTICIDES ON THE COTTON LEAF WORM SPODOPTERA LITTORALIS BOISD. (NOCTUIDAE: LEPIDOPTERA)

摘要

An experiment was conducted under laboratory condition to estimate the comparative efficiency of the least minimized concentration (LC4), each of thiamethoxan, emamectin benzoate, chlorfluazuron and chlorpyrifos against the 4th instar larvae of Spodoptera littoralis and to determine the inspected malformed forms of the developed immature and adult moths. The performance of Random Amplified Polymorphic DNA (RAPD) assay for the detection of the possible existing genetic polymorphism between the controland the treated Spodoptera littoralis larvae that occurred. For that purpose, ten primers namely: OPD-03, OPH-02, OPH-03, OPO-02, OPO-05, OPA-02, OPA-03, OPA-15, OPC-03 and OPD-02 were tested. The obtained results revealed that the toxicity of the tested insecticides increased as the exposure time increased. In this concept, Emamectin benzoate was the utmost toxic compound followed by chlorpyrifos, thiamethoxan and the least was the chlorofluazuron. In addition, RAPD data must be considered as preliminary, semi-quantitative, and that gave an overview of DNA effects. The tested primers revealed differences between the untreated and the treated samples with visible changes in number and size of the amplified DNA fragments. Polymorphism ranged from 32 tol00% as screened by the ten primers among all samples. Taking all data together, higher polymorphism was recorded at LC4 (82%) using primer OPC-03 and OPH-02. Definitely, RAPD data confirmed the results of the susceptibility test as well as the recordedindividual's malformation, which suggested that DNA damage and the possible occurring mutations may appear to be the main factor influencing the evident polymorphism between the untreated and the treated larvae.