The control of trichostrongyle larvae (Nematoda) by fumigation in relation to their bionomics

Abstract

A standard culture technique is described for obtaining the various developmental stages of Trichostrongylus colubriformis, and a suitable technique for assessing the effect of methyl bromide fumigations is outlined.Doses of 10, 25 and 150 mg. hr./l. were required to give an LD50 for eggs, pre-infective and infective larvae respectively. The age of infective larvae, the relative humidity and the temperature all influenced the toxicity of the fumigant. Soil, and more especially faeces, sorb the fumigant and probably protect larvae from its full effect. Infective larvae of T. axei, T. retortaeformis and H. contortus were also found to be susceptible to methyl bromide.The activity of larvae surviving fumigation was considerably reduced, but these larvae were still capable of infecting guinea pigs.Methyl bromide killed common pasture grasses at doses of 150–250 or more mg. hr./l., depending on the temperature. Chloropicrin was found to be highly toxic to grass and unsuitable where the pasture is required undamaged.The results are discussed in the light of current theories of the mode of action of methyl bromide on insects and what is known at present of the physiology of nematodes.It is concluded that under certain conditions, methyl bromide might be used to eliminate infestations of trichostrongyle larvae on pasture, without killing the pasture.I am indebted to Professor B. G. Peters and other members of the staff of the Imperial College Field Station and Dr C. W. R. Spedding of the Grassland Research Institute, Hurley, for their help in this work and their advice and criticism.