Larvicidal efficacy of a new semi-synthetic avermectin derivative
Methylamine avermectin (Radical 0.5% EC) was determined against larval instars of
the Egyptian cotton leafworm, Spodoptera littoralis (Biosd.) in the laboratory, field
and semi field experiments. 2nd and 4th instar larvae showed greatest susceptibility to
the Radical in the laboratory experiment. The LC50s values of the 2nd and 4th larval
instar after 48 hours were 0.005 and 0.008 ppm, respectively. Radical was tested with
recommended dosage (200 ml / 100 liter water) in field; it caused 84.6% reduction of
pest population up to day 8 post-treatment. On the other hand, the semi field
application of the same recommended dose on the 2nd instar larvae showed general
mean 73.6% mortality, 7 days after post-treatment. Also, some biochemical changed
in the 4th instar larvae after 48 hours of treatment with tested bioinsecticide were
measured. It’s clear from the results that activities of trehalase, invertase and
acetylcholine esterase were increased in all treatments. Tested bioinsecticide reduced
the activity of alkaline phosphatase at all doses compared to untreated larvae. No
significant changes in acid-phosphatase activities were observed at all treatment
doses. On studying the effect of esterases isozymes patterns, there were no differences
in number and position of esterases isozymes between untreated and treated larvae in
the whole larval body tissues although each band different in its concentration. The
toxicity of the formulation to some beneficial predators was also evaluated in the
field. There was no detectable effect of these bioinsecticide on naturally occurring
beneficial species. |
