A comparative Method for testing Agents used in Sheep Maggot Fly Control

Abstract

A controlled technique is described, whereby the comparative protective values of various dips and sprays used in sheep maggot fly control can be accurately assessed.In order to determine the exact mode of action of the agents under test, each is examined from the point of view of its power to inhibit oviposition by the adult fly and also for its larvicidal properties.The “anti-adult” test involves the weekly exposure of treated groups of sheep to an active and dense fly population, maintained in a closed chamber under controlled conditions of temperature and light.The larvicide test is a modification of a former method of larval implantation, and is applied to the sheep when the “anti-adult” protection, indicated by the previous test, is found to have failed.In the second part of the paper, a number of results are presented which serve to illustrate the working of the technique, and demonstrate the comparative value of several methods of maggot fly control which are in current use.A dip containing 0·5 per cent. DDT in water suspension was found to give the most satisfactory protection, and to achieve this result purely by its action against the adult fly. A 0·5 per cent. DDT benzene emulsion dip was less satisfactory, as alsowas spraying as a method of applying the insecticide. In general, spraying has given about half the protection of dipping, whilst on sheep in full fleece, the application of half a gallon of spray was found to be inadequate. Protection was again found to be poor when the fleece was carefully dressed with half a pound of a dry powder containing 5 per cent. DDT.In contrast to DDT, BHC and arsenic were shown to possess virtually no “antiadult” properties at the concentrations tested. BHC and arsenic both acted as efficient larvicides and provided a valuable and similar degree of protection against the sheep maggot fly, as an incidental effect, when they were tested at the concentrations normally used for their primary function of sheep scab control.