Eugregarines reduce susceptibility of the hide beetle, Dermestes maculatus, to apicomplexan pathogens and retard larval development.

Eugregarines are abundant in a great diversity of invertebrates, and yet their relationships with their hosts are subject to controversy and confusion. We tested the effect of the eugregarine, Pyxinia crystalligera, on growth, development, and susceptibility to two Apicomplexa pathogens of the hide beetle, D. maculatus. Heavy infection with eugregarines provided partial protection from two pathogenic members of Apicomplexa, M. trogodermae and A. tribolii. Infection with P. crystalligera caused lower weight in beetle larvae, but did not significantly retard pupation or adult emergence. A. tribolii infection of Lepidoptera and M. trogodermae infection of D. maculatus are reported for the first time.