Structure—activity relationships in pyrethroid esters derived from substituted 2-phenoxy-3-methylbutanoic acids

Non-cyclopropane pyrethroid esters of different substituted 2-phenoxy-3-methylbutanoic acids have been synthesised using the three alcohols—3-phenoxybenzyl alcohol, α-cyano-3-phenoxybenzyl alcohol and 3, 4-methylene-dioxybenzyl alcohol. Among the 35 esters synthesised and tested against Culex quinquefasciatus Say, the Bancroftian filariasis vector, for both larvicidal and adulticidal activities, α-cyano-3-phenoxybenzyl 2-(4-fluorophenoxy)-3-methylbu-tanoate, with an LC₅₀ value of 2.5 × 10^?3 mg litre^?1 for larvicidal activity, and α-cyano-3-phenoxybenzyl-2-(4-chlorophenoxy)-3-methylbutanoate, with an LD₅₀ value of 30 times; 10^?4 ug insect^?1 for adulticidal activity, were found to be as effective as fenvalerate, a well-known non-cyclopropane pyrethroid ester. Structure-activity studies showed that the insecticidal activity is dependent on the nature and position of the substituent in the phenyl ring of the acid moiety and also on the type of alcohol moiety.