| Summary: | Abstract Average yields of Mattesia spores (spore productivity) had varied from a minimum yield (0.17 × 107 spores) for Laemophloeus turcicus adult to a maximum yield (7.46 × 107 spores) for Plodia interpunctella larva. Comparatively, the highest increase in Mattesia spore yield, recorded from P. interpunctella larva (7.46 × 107 spores) over the lowest one, estimated for L. turcicus adult (0.17 × 107 spores), was nearly 44-fold. The increase in Mattesia spore yields that calculated from the other hosts (P. interpunctella pupa or moth; Galleria mellonella larva; Rhyzopertha dominica adult; Sitophilus zeamais), over that estimated for L. turcicus adult, was less than 10-fold (6–9-fold). Based on the weight of 1 g of the insect host infected with Mattesia sp., small stored grain insect hosts (e.g. L. turcicus, S. zeamais, and R. dominica) seemed to achieve Mattesia spore yields more than the larger ones (e.g. P. interpunctella). The increase in spore yields over that used for the inoculum, based on an average of 25 P. interpunctella larvae per bioassay container, was ca. 2 to 31-fold. These results revealed that the Indianmeal moth, P. interpunctella, could serve as a potential host for mass propagating the isolated entomopathogenic protozoan, Mattesia sp. Besides Mattesia larval mortality, survivors of Mattesia infection suffered deformities and noticeable undersized pupae or adults than the control ones. Also, many copulated moths (ca.46%) were unable to become separated after copulation until they had died. Bioassay of siftings, obtained from L. turcicus-protozoan-infected stock cultures, was carried out in order to emphasize the suppressive potent role of such protozoan entomopathogens in long-term storage. With the highest tested concentration of the studied siftings (10%), mortality responses due to Mattesia infection ranged from 13 to 68% at 14–169 days post-treatment. The corresponding figures for Adelina infection were 7–42%.
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