Relative susceptibility of populations of Amrasca biguttula biguttula (ISHIDA) infesting Bittergourd (memordica charantia L.) collected from different locations to insecticides part II
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Date
1994
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Department of Agricultural Entomology, College of Horticulture, Vellanikkara
Abstract
A study was undertaken at the college of Horticulture, Vellanikkara during 1993-94 to evaluate the relative susceptibility of eight different populations of Amrasca biguttula biguttula (Ishida) on bittergourd collected from four districts of Kerala state to six insecticides belonging to different chemical groups. Two different localities were selected for the collection of the leaf hopper, from each district. The selected localities were, Pattikadu and Nedupuzha (Thrissur district), Pothappara and Odanallur (Palakkad district), Wandoor and Chattipparambu (Malappuram district) and Vempalli and Kurichi (Kottayam district). All the populations were collected from farmers fields which were subjected to regular insecticidal spraying.
The insecticides selected for the study belong to different chemical groups viz. organophosphorus compounds (quinalphos, monocrotophos and phosphamidon), organochlorine compounds (endosulfan), synthetic pyrethroid (deltamethrin) and CHO compound (ethofenporx). Among these insecticides, the organophosphorus compounds were widely used by the farmers for controlling this pest in the field.
Relative toxicity of different insecticides to different populations were found by leaf dipping technique of bioassay and the results were subjected to probit analysis (Finney, 1971). Based on the relative toxicity studies it was clear that endosulfan was the most toxic insecticide against A.biguttula biguttula collected from all the eight localities. Monocrotophos ranked second in toxicity against populations from Thrissur district while deltamethrin was proved to be the second highly toxic insecticide to Palakkad and Kottayam hopper populations. Against Malappuram populations of A.biguttula biguttula highest toxicity of endosulfan was followed by ethofenprox. Phosphamidon was found to be relatively less toxic to this pest. Quinalphos, the commonly used organophosphorus insecticide was found to have least toxicity and thereby it was observed to be ineffective in controlling this pest in bitttergourd in all the four districts.
Great variation was observed in the relative toxicity values of different insecticides indicating their difference in toxicity level to A. biguttula biguttula. The order of toxicity of different insecticides was found to be the same between the two populations from each district but varied with populations from different districts.
Organophosphorus compounds were found to be relatively less toxic than endosulfan, deltamethrin and ethofenprox belonging to other groups. Therefore, the use of quinalphos against A.biguttula biguttula among the farmers has to be discouraged and endosulfan can be advocated against A. biguttula biguttula in bitterfourd as an alternative. Carbaryl was proved to be ineffective against leaf hopper populations in bittergourd earlier (Sabitha, 1992).
The relative susceptibility studies with populations of A. biguttula biguttula from the four districts revealed that all the eight populations were highly susceptible to endosulfan. The LC50 value of endosulfan was found to be very low, ranging from 0.00022 to 0.00041 per cent. At the same time all the populations were least susceptible to the most commonly used organophosphorus insecticide quinalphos. All the populations showed higher susceptibility to endosulfan, deltamethrin and ethofenprox than the organophosphorus insecticides. Thrissur population was more susceptible to monocrotophos next to endosulfan. Palakkad and Kottayam populations were more susceptible to deltamethrin while Malappuram populations indicated more susceptibility to ethofenprox, next to endosulfan. The LC50 value of phosphamidon ranged from 0.02 to 0.06 and all the eight populations of A.biguttula biguttula manifested lower susceptibility to this insecticide in comparison with the other chemicals
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