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Although structure modifications of natural pyrethrin constituents have disclosed a variety of potent synthetic analogues, all known examples are cyclopropanecarboxylate esters, a grouping that appeared to be essential for insecticidal activity. Some new substituted 2‐phenylalkanoates, whose biological activities are of a similar nature and potency to those of conventional pyrethroids, are now reported. 5‐Benzyl‐3‐furylmethyl and 3‐phenoxybenzyl 3‐methyl‐2‐phenylbutyrates and their analogues are potent insecticides. Activity is increased on the introduction of appropriate groups into the 3 and/or 4‐positions of the aryl ring and the (S)‐2‐phenylalkanoates are far more active than their (R)‐enantiomorphs. Structure/activity relationships are compared with those for conventional pyrethroids. Some of the new series compare favourably with typical insecticides in tests against Musca domestica, Spodoptera litura and Plutella xylostella.

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Thirteen pyrethroid‐type esters of substituted 1(or 3)‐hydroxymethylimidazolidine‐2, 4‐dione were synthesised and their knockdown activities against houseflies, mosquitoes and cockroaches were examined. Knockdown activities of 2,4‐dioxo‐1‐prop‐2‐ynylimidazolidin‐3‐ylmethyl esters in oil solutions were higher than those of known knockdown pyrethroids; three of the compounds also possessed strong knockdown and flushing‐out activities against cockroaches.

A B S T R A C TPjlrethroid insecticides are churucterised by high knockdown and lethul uctivity, a wide spectrum, good residuul activity, together with repellent and antijeeding activity. With these characteristics, pyrethroid insecticides huve become widely used for plant protection. Their major use has been for the control of bollworms and leafworms in cotton but they have also uchieved widespread use for controlling various species of lepidopterous pests in jriiits and vegetables, aphids in cereals, and marly other minor outlets. Although the early synthetic pyrethroids surered ,from a lack of uctivity against mites and soil pests, later additions, such as &npropathrin, have combined high acaricidal activity with insecticidal activity und .further pyrethroids ure being introduced for use in soil.The extent of pyrethroid use has increased progressively since the ,first oj' the 'photostable' pyrethroids was registered. In 1986, the market shure qf pyrethroids reached 25 ? A of the totul insecticide market ,for plant protection; this j g u r e cun be increased in the ,future.

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