Toxicity of endogenous soil Actinomycetes against larvae of Culexpipiens (Culicidae- Diptera)

Abstract

Fifty seven actionmycetes isolates were isolated from different Egyptian sites. Only 25 isolates showed larvicidal activity against 3rd instar larvae of Culex pipiens mosquito. The isolates which had high larvicidal activity were selected for further investigation. Metabolites of this actionmycetes isolates not only proved its toxicity against larvae of Culex pipiens but its cytotoxic effect were extended to the pupal and adult stage. The metabolites affect the insect body protein as well. Two isolates from the selected isolates, 110 and 108 showed chitinase activity with inhibition zone 3.4 and 2.3 cm, respectively. The isolate 110 was more toxic than the isolate 108 with LC50 values 3.18±1.44 and 5.02± 1.59ml/100 ml H2O after 72 hrs. post treatment, respectively. Both isolates affect insect body proteins and changed its configurations. Histopathological signs after treatment proved that the two isolate metabolites are gut toxins and affect the body wall and fat tissues. The isolate 110 was identified to species level depending on 16S rRNA gene analysis as Streptomyces griseoflavus.