Abstract
A study was made of the seasonal variation in population density of larvae of Boophilus microplus (Can.) in four locations in Jamaican pastures where the mean annual precipitation ranged from 59 to 222 cm. Variations in population density were related to rainfall. Generally, four months of heavy rains in August to November preceded significant increases in B. microplus populations in December to February. This was followed by a reduction then another slight increase, resulting in a bimodal pattern of activity. Although populations fell to very low levels by the end of the dry season, only in one focus were they depleted to undetectable levels.