The persistence of pyridalyl,
emamectin-benzoate, spinetoram, hexaflumuron, and chlorpyrifos on cotton (Gossypium
barbadense, var. Giza 86) and castor bean (Ricinus communis)
foliages under field conditions, via bio-determination of median lethal time
(Lt50) values, and their efficacy against the 4th instar
larvae of Spodoptera littoralis (Boisd.) laboratory strain were
investigated. The local and systemic activities and fastness against washing
with water of the tested insecticides on cotton and castor bean were studied as
well. Pyridalyl residues were significantly the most persistent on castor bean
and cotton plants with Lt50 values of 14.91 and 9.93 days,
respectively. On the contrary, spinetoram had the least persistent residues on
castor bean and cotton recording Lt50 of 0.20 and 1.06 days,
respectively. With exception of pyridalyl, the tested insecticides were
significantly more persistent on cotton than on castor bean plants. Pyridalyl
and emamectin-benzoate proved to be the most effective against the 4th
instar larvae of S. littoralis that fed on treated cotton plants. When
the larvae were fed on treated castor bean plants, pyridalyl and hexaflumuron
resulted in the superior percentages of larval mortality. The insecticides
implicated in this study did not demonstrate any appreciable systemic
activities in cotton or castor bean plants against the 4th instar
larvae of S. littoralis, although they possessed strong local
activities. The initial deposits of chlorpyrifos, pyridalyl, hexaflumuron, and
emamectin-benzoate were significantly more stable on sprayed castor bean plants
than on sprayed cotton plants versus elimination and washing with water. The
initial deposit of spinetoram was completely unstable on sprayed cotton or
castor bean plants. These results indicated that the kind of the treated host
plant is very effective factor in toxicological properties of the tested
insecticide and this could be useful in bio assay experiments design.