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Abstract
Assessments were made on the influence of several microclimatic variables on the availability
of third-stage larvae of Haemonchus contortus and Haemonchus placei on four strata
of irrigated Kikuyu pasture. Three replicates of these pasture samples were collected
on 18 sample days over 12 months and the log10 mean counts of the larvae recovered
were analysed by a step-wise regression model. Predictors for the log counts of the
four strata for the two nematode species included relative humidity, illumination,
air temperature and windspeed. The effect of air temperature on larvae of both Haemonchus
species was similar; as air temperature increased, the number of larvae on pasture
increased. The inverse was true for windspeed; as windspeed increased larval counts
decreased. For H. contortus, relative humidity increased as the number of larvae increased
on all strata except upper herbage. The R2 values ranged from 0.11 to 0.21 for H.
contortus and from 0.04 to 0.12 for H. placei. Under the conditions of this study,
only 21% of the effect on H. contortus and 12% on H. placei third-stage larvae on
pasture can be explained by microclimatic conditions.