COS 65-5 - Targets of aggressive competitive behaviors in an introduced solitary wool carder bee

Abstract: Pollinators provide a critical ecosystem service but are generally declining. While insect pollinators can be successfully conserved in urban and suburban areas, non-native species can be more abundant in cities and have the potential to limit conservation efforts. For example, Anthidium manicatum is a solitary wool carder bee that was first documented at our research site in 2016. Male A. manicatum are territorial and engage in both intraspecific and interspecific competitive aggressive behaviors in the vicinity of specific flowering plants. The objective of our research was to evaluate the relative frequency of attacks and other interactions of male A. manicatum with pollinator species and compare those to the abundance of potential targets. We conducted our research from 2020-2022 on Gonzaga University’s campus located near downtown Spokane, Washington. Honey bees, wool carder bees, at least eight species of native bumble bees, and several solitary bees and wasps occur at our field site. Our methods consisted of live observations of A. manicatum behavior, mark-resight methods, video recordings, and live timed counts of floral visitors on ornamental blue salvia to quantify interaction frequency and the relative abundance of potential targets. In all three years, honey bees were the most abundant pollinator at our site. In proportion to their abundance, honey bees were also the most frequent targets of A. manicatum’s attacks. During all three years, male A. manicatum attacked conspecific rivals at a greater rate than expected from their abundance relative to honey bees. Data from 2021 and 2022 were sufficient for us to examine weekly patterns in abundance and interaction rate. In 2021, the week-to-week correlation between the abundances of A. manicatum and honey bees was negative, while in 2022, A. manicatum and honey bees were not significantly correlated from week to week. During the three weeks when A. manicatum’s per capita rate of attacking interspecific competitors was highest, interspecific targets were between 2.4 to 8 times more abundant than male wool carders. We suggest that A. manicatum has negative effects on other pollinators and is a concern from the perspective of pollinator conservation. However, A. manicatum might have limited ability to exclude interspecific competitors from flowers because it disproportionally targets conspecifics. Therefore, A. manicatum might be tolerated in gardens and its impact mitigated by growing flowers that attract rarer pollinators.