Gromphadorholaelaps schaeferi is a symbiotic mite associated with the Madagascar hissing cockroach Gromphdorhina portentosa. The population structuring of G. schaeferi is described based on examination of 19,421 mites collected from 1,915 individuals of G. portentosa taken from a large laboratory colony. The mites exhibited an overall prevalence of 50.7% and mean intensity (+SE) of 20.0 (+0.6) with an infestation intensity range of 1-116, and relative abundance (+SE) of 10.1 (+0.4). Both prevalence and mean intensity of infestation exhibited a dramatic increase with increasing cockroach size/age. By the time cockroaches reach 40 mm the prevalence is nearly 100%. Mean intensity increases with cockroach length up to about 60 mm and then levels off at about 43 mites/cockroach. Overall, the mite distribution among cockroaches exhibited pronounced overdispersion with a variance to mean ratio of 30.1 and k value of 0.182101. Nevertheless, the distribution of mites on G. portentosa did not conform to expected values of the “classic” negative binomial distribution due to a greater number of moderate infestations than expected and a lower number of heavy infestations than expected.

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