STUDIES ON GENETIC IMPROVEMENT OF GREEN LACE WING CHRYSOPA SCELESTES BANKS (NEUROPTERA : CHRYSOPIDAE) : SELECTION FOR MONOCROTOPHOS RESISTANCE
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Date
1993
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AAU, Anand
Abstract
Studies were carried out to develop genetically improved monocrotophos resistant strain of green lace wing, C. scelestes during 1989-92 at Biological Control Laboratory of Gujarat Agricultural University, Anand Campus. Monocrotophos was selected as test insecticide because it proved effective against jassids as well as very toxic to C. scelestes and commonly used in cotton ecosystem. Severe pathological changes were observed when histopathological studies were conducted. Of the three bioassay methods tried, topical application was found better and with insecticidal pressure for 9 generations, the strain could be improved to resist 0.047% of monocrotophos. This method gave higher resistance index (442.38). While at same number of generation, food impregnation and film exposure method, showed 4.06 and 1.00 resistance index respectively. The dosage mortality regression lines moves to the right in successive generation and consequently the LC50 value increases. The resistance developed in C. scelestes was observed to reverse in third generation when selection pressure of insecticide was relaxed. Resistance index was 12.518 and 15.44 for R/P and R/S respectively. The monocrotophos resistant strain showed cross resistance to dimethoate 0.03%, acephate 0.075%, phosphamidon 0.03% and methyl-o-demeton 0.03%, but did not show resistance to quinalphos 0.05%, triazophos 0.05%and amitraz 0.1% through belonged to the same group. Possible explanations are given. Biological studies revealed that the larval period was significantly shorter in resistant strain as compared to susceptible strain. Similarly pre-oviposition, oviposition and post-oviposition was also lower in resistant strain. The resistant female laid lesser number of eggs. Morphometric differences were also observed in the larval and pupal stage. Biochemical analysis revealed that resistant strain had higher amounts of I lipids and higher activity of Acetyl cholineesterase enzyme (AchE) than the susceptible strain. Possible reasons for imparting resistance are explained in detail. Genetic analysis of monocrotophos resistance showed that additive as well as epistasis type genes were found to play important role in the expression of larval length of first instar. Toxicological tests revealed that additive as well as non-additive gene effects controlled the expression of this trait. It suggested the polygenic nature of inheritance for monocrotophos resistance in C. scelestes. The collection of C. scelestes from different geographic regions showed wide variation in their biological characteristics and response to monocrotophos. Resistant as well as susceptible strain integrated with monocrotophos gave effective control of aphids and jassids when open and confined releases were made. However, susceptible strain proved ineffective against B. tabaci confirming its susceptibility to monocrotophos. The resistant strain remained unaffected by monocrotophos and gave effective control of B. tabaci. The monocrotophos resistant strain of C. scelestes and its ability to cross resist to some of the insecticides, offers great scope for developing a sound integrated pest management approach in general and particularly in cotton ecosystem.
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AGRICULTURAL ENTOMOLOGY, AGRICULTURE, A STUDY