CARPENTER BEE NECTAR ROBBERY EFFECTS ON FRUIT QUALITY AND NESTING PROVISIONS IN RHODE ISLAND

Eastern carpenter bees, Xylocopa virginica L., are among the most abundant native bee visitors to highbush blueberry flowers in Rhode Island, and they frequently slit corollas to rob nectar. My objective was to assess if nectar robbery offsets the possible value of X. virginica as a native pollinator of blueberries in Rhode Island. I studied foraging behavior of X. virginica at the Rhode Island Agricultural Experiment Station planting which consists of 14 highbush blueberry cultivars. I assessed plant and environmental factors related to slitting behavior, and the effects of slitting on fruit set and blueberry quality. The average number of flowers that X. virginica visited per minute was significantly influenced by time of day, temperature, and sex, but the time spent per flower was not. The frequency of corolla slitting by carpenter bees among 14 cultivars during bloom averaged 35% slit flowers (range 16 – 67% ‘Earliblue’ and ‘Lateblue’ respectively) in 2017, and 39% (range 20 – 62% ‘Bluecrop’ and ‘Collins’ respectively) in 2018. Plant and environmental factors that affected the proportion of corollas slit included cultivar, anther length, flower volume, and number of days in bloom at or above 15oC. Corolla slitting did not affect fruit set. Average fruit weight and percent soluble solids resulting from slit and non-slit corollas did not differ significantly in two early- (‘Bluehaven’, ‘Earliblue’), two mid- (‘Collins’, ‘Bluecrop’), and two late-season (‘Herbert’, ‘Lateblue’) ripening cultivars in 2017. In 2018, average fruit weight and percent soluble solids resulting from slit and non-slit flowers did not differ significantly in most cultivars, but slit flowers resulted in berries with greater mass in two cultivars, ‘Bluehaven’ and ‘Collins’. ‘Collins’ fruit from non-slit corollas had a significantly higher percentage of soluble solids at maturity than fruit from slit corollas in 2018. Corolla slitting and nectar robbery by X. virginica did not have a significant negative effect on fruit quality under our growing conditions and pollinator community. Understanding the nesting and foraging habits of Xylocopa virginica can aid in efforts to recruit natural populations to crops for pollination services. Measurements of Xylocopa virginica nest tunnels and cells were similar to those reported in previous studies. Analysis of pollen loaves showed that X. virginica provisioned pollen loaves from 21 different genera of plants in 2016, 19 in 2017, and 39 in 2018. Antirrhinium majus (Garden snapdragon) made up the majority (21.4%) of pollen collected in all three years. Blueberry pollen was a minor component of pollen loaves (0.1%). Only two of 168 trap nests deployed in 2017 were occupied by a total of ten X. virginica bees. However, 33 nests (19.6%) hosted 230 Osmia taurus, 73 Osmia cornifrons, and 8 Osmia lignaria Thirty-four nests (20.2%) were occupied by 151 grass-carrying wasps, Isodontia sp. and 6 vespid wasps occupied two nests (1.2%) in 2017. In 2018, four of ninety-six trap nests were occupied by carpenter bees