Efficiency of some new insecticides on physiological, histological and molecular level of cotton leafworm.

Abstract

Efficiency of indoxacarb, spinetoram and methoxyfenozide on cotton leaf worm (Spodoptera littoralis) was determined through exposure of second and fourth instar larvae to dipped castor bean leaves. LC50 estimates of second instar larvae ranged from 0.004 to 0.006 ppm of indoxacarb, 0.022 to 0.033ppm of spinetoram and 0.006 to 0.011ppm of methoxyfenozide. LC50 estimates of fourth instar larvae ranged from 0.36 to 0.54 ppm of indoxacarb, 1.78 to 2.64ppm of spinetoram and 1.36 to 1.69 ppm of methoxyfenozide. Also, the ovicidal activity of these compounds was studied. Three day old eggs are more affected than that of one or two days old in case of indoxacarb and spinetoram while the reverse was in the case of methoxyfenozide. In nutritional assays, all tested compounds reduce food intake and affected growth rate (GR) where indoxacarb caused the highest rate of efficiency and followed by methoxyfenozide and spinetoram against 4 th larval instar fed for two days on castor leaves treated with LC50s of the previous coumpounds. The histological examinations of 6 th larval instar cuticle (after treatment of fourth larval instar by LC50 of methoxyfenozide) showed destruction in the cuticle layers, fissures in the endocuticle and irregular distribution of the hypodermal cells. While indoxacarb and spinetoram treatments showed slight effect in the cuticle layers as compared to methoxyfenozide. In addition, the deteriorative potentialities of aldehyde oxidase and α glycerophosphate dehydrogenase pattern of S. littoralis were screened.