Microbial control of the cotton leafwonn by bacteria and its preparations

Abstract

Laboratory experiments were carried out to study the efficacy of bacterial commercial insecticides of B. thuringiensis ( Berliner ) ; namely Dipel 2X , Dipel EC and Ecotech Bio on the different growth stages of S. Littoralis ( Boisd .) . The treated stages included treatments of the 6 larval instars with 6-7 concentrations of the bioinsecticides . Data were recorded from the tested larvae and subsequent stages and included mortalities , malformations, egg-laying of the resulting adults and hatchability percentages amongst the deposited eggs . Studies extended also to include the field studies by spraying Dipel 2X on cotton plants artificially infested by S. Littoralis egg- masses , and after that the percentages of infestation to cotton leaves was estimated . On the other hand , the detrimental effect of UV and that of direct sunlight on B. thuringiensis spores was estimated by laboratory and field studies . Trials were also made for protection of B. thuringiensis spores from UV by adding different materials (shellac, melanin and neste- coffee) . Studies extended also on endotoxin material prepared by genetic engineering which proved from the presented study as more tolerant to UV than the common commercial bactericides . Studies included also the effect ofDipel2X treatment to the 2nd and 4th larval instars on S. littoralis haemolymph (total haemocyte counts, THC's and DHC's ) and also the histopthologicl effect of the same preparation on the mid - gut of S. littoralis by treatment of the l st and 3rd larval instars .