The Action of the systemic Insecticide Fluoroacetamide on certain Aphids and onPieris brassicae(L.)

Abstract

Fluoroacetamide has been tested as a systemic insecticide againstAphis fabae Scop.,Brevicoryne brassicae(L.),Myzus persicae(Sulz.) and the eggs and larvae ofPieris brassicae(L.). In the majority of tests, sodium fluoroacetate and schradan have been included for comparison.In dipping tests againstA. fabaeandB. brassicae, fluoroacetamide was as effective as sodium fluoroaeetate and both were much superior to schradan. Fluoroacetamide was superior to sodium fluoroacetate in preventing eggs ofP. brassicaefrom hatching and they were about equally effective against the newly hatched larvae. Schradan was already known to have little action on the eggs or larvae. Neither of the fluorine compounds was very effective against fourth-instar larvae.When watered on to the soil, fluoroacetamide was more readily absorbed from sand than from soil—like other systemic insecticides. AgainstA. fabaeit was as immediately effective and persistent as sodium fluoroacetate and both were superior to schradan. ToB. brassicaeandM. persicae, fluoroacetamide was more toxic than sodium fluoroacetate,M. persicaebeing somewhat more resistant to fluoroacetamide and much more resistant to sodium fluoroacetate. Slight phyto-toxic effects were observed only at the higher dosages.When poured on to the soil around the roots of cabbage plants, neither compound prevented eggs ofP. brassicaefrom hatching, but the young larvae were killed when they began feeding. Applied systemically in this way, fluoroacetamide was more toxic than sodium fluoroacetate to these young larvae and to fourth-instar larvae.When John Innes potting compost was treated with solutions of the fluorine compounds and stored in the greenhouse it was found that both compounds were quickly decomposed at the dosages necessary for systemic action against aphids, but higher dosages were much more persistent.In solution, given systemicallyviathe roots to broad beans, fluoroacetamide and sodium fluoroacetate were about equally effective and both were more toxic than schradan toA. fabae. Fluoroacetamide was the more toxic of the fluorine compounds.The technique of the cut tap-root showed that the approximate LD 100 forA. fabaeon broad beans was: fluoroacetamide between 0·09 and 0·9 mg./kg.; sodium fluoroacetate 0·7 mg./kg.; schradan 50 mg./kg. When taken up by cabbage leaves through the cut petioles, 5 mg. of the fluorine compounds or 50 mg. of schradan per kg. of fresh plant tissue killed allB. brassicaein 2–3 days.Leaves of cabbage treated in the same way with fluoroacetamide were fed to larvae ofP. brassicae. It was found that the growth of the larvae feeding on the leaves was not prevented until a dose of about 20 mg./kg. was reached. The same value was found for sodium fluoroacetate. For schradan, more than 2,900 mg./kg. were required.Finally, with applications made to the older leaves against all these species of aphids feeding on the younger leaves of their host-plants, fluoroacetamide was equally effective or slightly superior to sodium fluoroacetate as a systemic insecticide. Schradan was nearly as effective againstB. brassicaebut much less effective against the other two aphids.Even after repeated applications none of the compounds acting systemically prevented eggs ofP. brassicaefrom hatching or had a detectable toxic action on fourth-instar larvae.