The biological activity of some chitin synthesis inhibitors against the cotton leafworm Spodoptera littoralis (Boisduval), (Lepidoptera: Noctuidae)

The action of three chitin synthesis inhibitors insecticides (chlorfluazuron, teflubenzuron and flufenoxuron) against third and fifth instars of both susceptible and field strains of cotton leafworm Spodoptera littoralis, (Lepidoptera: Noctuidae), were carried out in order to investigate the biological activity of these compounds, in their formulation form, under controlled laboratory conditions. The estimated LC50 values, clearly showed that the third instars were more sensitive to the compounds tested, compared with those of the fifth instars, regardless of strain used. Data from larval dietary bioassay showed an up to 4-fold in LC50 values among the strains tested. Such values, expressed as tolerance level depended largely on the chemical tested and/or the instar used. The tolerance level calculated for the third instars was generally less than that corresponding for the fifth instars, irrespective of compounds tested. The highest tolerance level recorded was observed for chlorfluazuron, whereas the lowest pertained to teflubenzuron. The percentage of accumulative mortality varied according to the compound, concentration, the instar larvae and/or strain studied.