Individual nymphs of the predaceous pentatomid Podisus maculiventris Say were each fed a single first instar Douglas Fir tussock moth larva, Orgyia pseudotsugata McDunnough, and held without further feeding at constant temperature for a known number of days before being frozen. Enzyme-linked immunosorbent assay, ELISA, was used to examine these predators for the presence of prey antigens. The concentration of prey antigens in these predators declined at a linear rate over the 7 days they were held post-feeding. Detectable antigens remained in 50% of the predators after three days at 24°C. On the day in which the prey was consumed (day 0) only 80% of the unstarved predators had detectable prey antigens which suggests the possibility of instinctive killing of prey with little or no subsequent ingestion. The amount of prey antigen in molted and unmolted predators was not statistically distinguishable; although molting interrupts feeding, digestion of the antigen(s) employed in this study seems to be continuous.

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The spore load of Ascosphaera species spores on larval chalkbrood cadavers and newly emergent adults of the alfalfa leafcutting bee, Megachile rotundata, was determined. The spore content of chalkbrood cadavers ranged from 3 x 106 to 5 x 108. Adults emerging through zero to nine cadavers carried spores on all body parts examined by scanning electron microscopy. Estimates of the total number of spores obtained from a series of adult washes ranged from 9 x 104 to 8 x 107. Some adult males which emerged through no cadavers carried 104 to 105 spores, indicating that nesting materials might also have been contaminated. However, the control of chalkbrood in commercial bee populations may not be accomplished simply by providing clean nesting materials as adults may still emerge through diseased larvae.

Summary — Twenty-nine cell series of the leafcutting bee, Megachile rotundata (Fabr), each containing 5 or more healthy larvae, no chalkbrood (Ascosphaera aggregata Skou) and no pollen masses were isolated from a population with over 36% chalkbrood. This selected subpopulation was split and isolated for 4 and 6 generations before being challenged by forcing the females to nest in heavily contaminated media, or by weekly dustings with approximately 175 x 10 8 A aggregata spores. The incidence of chalkbrood in both challenged lines was markedly lower than that of the wildtype, and comparable to that of the selected lines, suggesting a genetic component for resistance in both lines. The very low incidence of pollen masses (dead eggs or early instar larvae) in the selected lines throughout the 4 yrs of the study indicates that this trait may also be genetically mediated, either linked to, or independent of disease resistance.