ARTHROPOD/HOST INTERACTION, IMMUNITY Seasonal Variation of North American Form of Gigantolaelaps mattogrossensis (Acari: Laelapidae) on Marsh Rice Rat in Southern Coastal Texas

The ectoparasites of a small mammal community within an intertidal zone in the upper Gulf coast region of Texas were studied to assess the seasonal variation in abundances of the mite Gigantolaelaps mattogrossensis (Fonseca) (Acari: Laelapidae) on the marsh rice rat,Oryzomys palustris (Harlan). Further study into the ecology and dynamics of this parasiteÐhost relationship was deemed to be necessary to expand the understanding of these potential participants in the ecology of BayouHantavirus, an important causative agent ofHantavirus pulmonary syndrome. The objective of this study was to determine the effects of Þve predictor variables on mite abundance: prevalences of hosts, relative humidity, precipitation, temperature, and length of daylight. Mite abundance was modeled as a function of the Þve variableswith analyses of variance andmultiple regressions; however, because the predictor variables pertain to the sampling period rather than to the individual rodent host, the effective sample size was small and thus the sums of squares and cross products matrix was singular. We therefore developed and used a new method for estimating regression coefÞcients based on the “noise-addition method” (random residual variation) combined with a bootstrap step converting the reduced rank data to full rank, providing realistic estimates of conÞdence intervals for the regression statistics. The population abundances of mites ßuctuated signiÞcantly across collecting periods. Humidity and precipitation were the most inßuential variables in explaining the variation in abundances of mites. Model interpretation suggests that G. mattogrossensis is a nidicolous parasite. These results provide a baseline understanding of the seasonal interactions between parasite and host.