As a result of some major problems that come from using insecticides, the use of safe alternatives to these pesticides has become very necessary. Thus, a novel series of predicted toxicologically active urea, thiourea, thiosemicarbazide, oxadiazole, pyrazole, and triazine derivatives have been synthesized in a pure form to be lufenuron analogues as insect growth regulators which were screened and examined against Spodoptera littoralis (Boisd). The structure of synthesized compounds was established by means of spectroscopic and elemental analyses. Compounds b5, b2, b3, and a4 showed high insecticidal toxicity, and their LC50 values for the second larvae instar were found to be 26.63, 46.35, and 60.84 ppm, respectively, whereas the LC50 value for lufenuron as a reference insecticide was 17.01 ppm.

Due to the complicated problems coming from excessive applications of insecticides, searching for safe substitutes to these insecticides has become a necessity. Thus, the insect growth regulators are candidates to be used in such concern. Comparative studies of the effects of three compounds, 2-benzoyl-N-phenylhydrazine-1-carbothioamide (1), 2-(cyanoacetyl)-N-phenylhydrazine-1-carboxamide (2) and N-(2-(2-cyanoacetyl)hydrazinecarbonothioyl)furan-2-carboxamide (3) (an insect growth regulator inhibiting chitin synthesis), were conducted on Spodoptera littoralis (Boisduval, 1833). The compounds, orally administered, caused larval mortality proportional to the concentrations in the food source. larvae were unable to complete the molting process and died in the old larval cuticle. Larvae contaminated by sublethal doses completed their development to adulthood. N-(2-(2-cyanoacetyl)hydrazinecarbonothioyl)furan-2-carboxamide (3) is more active than the other compounds have LC50 17.082 ppm for 2nd instar larvae and 60.832 ppm for 4th instar larvae.

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In this article, series of semicarbazide, thiosemicarbazide, urea and thiourea derivatives have been successfully prepared via an easy synthetic strategy. The chemical structure of the prepared compounds have been confirmed based upon spectral and elemental data. The compounds showed excellent insecticidal activity against Spodoptera littoralis which causes a harmful damage to the cotton crop which represent a principal figure in economics of North Africa countries. Among all the prepared compounds, methyl-4-{[(4-chlorobenzoyl)carbamothioyl] amino}benzoate 7 showed the highest insecticidal activity against S. littoralis, with LC50 values of 9.882 for 2nd instar larvae & 102.66 for 4th instar larvae, respectively. Graphical abstract

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