The response of Tribolium confusum to sublethal levels of 2 environmental stressors was studied, i.e., parasitic infection represented by the cestode Hymenolepis diminuta, and a physical stressor represented by the natural pesticide diatomaceous earth (DE). These were applied sequentially (DE, then infection) to detect indirect or carryover effects of DE, and concurrently (DE applied immediately after exposure to parasites and DE presence maintained throughout the infection) to detect direct effects of DE. DE alone, but not parasitism alone, produced significant host mortality, and concurrent treatment with DE and parasitism did not increase mortality over DE alone. Parasite abundance was significantly higher following sequential, but not concurrent, DE exposure. Parasite abundance in mated hosts was significantly higher than in virgin hosts. Parasitic infection resulted in significantly fewer eggs retained in the oviduct of beetles, but there was no difference in the number of eggs that accumulated in the culture medium and no difference in the surface-seeking behavior of beetles. Mating status of beetles in all treatments, and DE exposure in concurrent treatments significantly increased their surface-seeking behavior. Concurrent exposure to DE also resulted in a 4- to 6-fold increase in host egg numbers that accumulated in the culture medium. Although DE exposure increased parasite numbers in the beetles, these 2 stressors otherwise appeared to act independently.