This study was carried out to evaluate the activity of some enzymes in cotton leafworm, Spodoptera littoralis (Boisd.). The fourth instar larvae were treated with LC50 values of certain insect growth regulators i.e. teflubenzuron, methoxyfenozide and tebufenozide as well some biocides i.e. spinosad and Dipel 2X (Bacillus thuringiensis) compared with an OP compound; chlorpyrifos. All tested compounds were evaluated after 72 hours with the exception of chlorpyrifos after 24 hours of treatment.
Generally, all the tested compounds caused significant decrease in the activities of amylase and trehalase enzymes comparing to control in the supernatant of S. littoralis larvae. Likewise, the tested treatments caused irregular results in the activity of invertase enzyme. Methoxyfenozide and spinosad showed significant increase in its activity, whereas teflubenzuron, chlorpyrifos, Dipel 2X and tebufenozide significantly decreased the activity.
As regard to the lactate dehydrogenase (LDH) enzyme activities chlorpyrifos showed remarkable significant increase (112.48 % relative to control). Spinosad gave a slight increase in the activity (101.44 % of control). On the other hand, the rest treatments caused reduction in LDH activity that recorded (95.35, 88.74, 71.59 and 53.56 % of control) for methoxyfenozide, teflubenzuron, Dipel 2X, and tebufenozide, respectively.
The activities of acid and alkaline enzymes were generally reduced as affected by all treatments than control.
The tested insect growth regulators significantly elevated the chitenase activity comparing to control, record 153.58 % for tebufenozide followed by teflubenzuron (136.29 %) and methoxyfenozide (102.39 %).
Results also showed changes in the activity of acetylcholine esterase in S. littoralis larvae. Spinosad gave significant increase comparing to its control (150 %). In contrary, chlorpyrifos recorded significant reduction as compared to control (63.72 %).
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