The Pathogenic Effects of Some Bioinsecticides on Culex pipiens L.(Diptera: Culicidae)

Abstract

The present study examined the pathological effectiveness of two entomopathogenic fungi (Beauveria bassiana andMetarhiziumanisopliae) against 3rdinstar Culex pipienslarvae in the laboratory. As judged by a comparison of LC50 values resulted from the bioassay test, Metarhizium anisopliaewas more effectivewith a recorded LC50 value of 0.36X108 spore/mlthanBeauveria bassiana with an obtained LC50 value of 0.72X1011 spore/ml.The biochemical effects of the two entomopathogenic fungi were studied.Results revealed significant reduction in the total proteins of the treated Cx. pipiens larvae compared to the control larvae.Protein analysis usingSodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) revealed that there was a reduction in the number of protein bands due to the treatment with either of the two fungi. Light microscopy and transmission electron microscopy were used to examine different tissues of the control and treated larvae including cuticle,muscles, andmidgut.Examination of several tissues of the treated larvaerevealed that the epicuticle layer is completely deformed and detached.Muscles were gradually disorganized over the treatment time in treated larvae with appearance of rupture and tearing in the muscles. In addition, the mid gut epithelial cells showed loss of microvilliat the midgut cell apex and loss of adhesion between adjacent cells. Moreover, deeply altered intracellular organelles gave rise to vacuoles in the cytoplasm of the epithelial cells.