Pollination, usually considered a mutualism, may in some cases be a type of parasitism. When the presence of a less effective pollinator reduces the number of pollen grains available to a more effective pollinator, the less effective pollinator is, in effect, a pollen parasite. The effectiveness of hymenopteran pollinators of Penstemon strictus (Scrophulariaceae) was measured in the summers of 2002 and 2003 in south-central Colorado. Hymenopterans were allowed to visit flowers and the proportion of pollen removed was measured. There was a significant effect of pollinator type and of behavior. The number of pollen grains deposited by different types of insect pollinators was also measured. To judge pollinator importance, the above data was combined with data on visitation rates. The data were used to parameterize models of the degree of mutualism or parasitism exhibited by each species.
Species 1: Hymenoptera Apidae Bombus (bumble bee)
Species 2: Hymenoptera Megachilidae Osmia (mason bee)
Keywords: pollination efficiency, mutualism
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