Assessments were made of the influence of several microclimatic variables on the availability of third-stage larvae of Ostertagia ostertagi, on pasture herbage. Variables most closely related to recovery of larvae from the lower herbage samples were: maximum air, mat and dung temperatures. Recovery of larvae from the upper portion of the herbage was closely correlated with dung temperature, sampling-time air temperature and maximum air temperature. Bearing in mind that the moisture threshold was maintained throughout the trial the results of this study suggest that under field conditions, larval movement of third-stage 0. ostertagi larvae on herbage is regulated primarily by temperature.
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