The Effect of Weather on the Development and Survival of the Free-Living Stages of Nematodirus spathiger (Nematoda: Trichostrongylidae)

Abstract

A 4-year study is reported on the effect of southwestern Montana weather on the development and survival of Nematodirus spathiger of sheep. Development of ova occurred during nearly any season of the year except the coldest months of the winter. Most rapid development took place from April through September. Development was slow and few embryos developed to the infective stage from October through March. Infective larvae survived longest in the cool or cold seasons. At least 10% of the larvae could survive the winter. The complex of relatively slow development and long survival of the free-living stages of N. spathiger indicates that the largest numbers of infective larvae occur on pasture in spring. It is inferred from the data that the agents most detrimental to the free-living stages of N. spathiger are sunlight and a high soil-surface temperature.