Osmia lignaria (Hymenoptera: Megachilidae) increase pollination of Washington sweet cherry and pear crops

Authors: McCabe, Lindsie; BOYLE, NATALIE - Pennsylvania State University; PITTS-SINGER, THERESA - Retired ARS Employee

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2024
Publication Date: 7/4/2024
Citation: McCabe, L.M., Boyle, N., Pitts-Singer, T.L. 2024. Osmia lignaria (Hymenoptera: Megachilidae) increase pollination of Washington sweet cherry and pear crops. Environmental Entomology. https://doi.org/10.1093/ee/nvae043.
DOI: https://doi.org/10.1093/ee/nvae043

Interpretive Summary: Honey bees are important pollinators for orchard crops worldwide. However, because renting beehives for pollination can be expensive and uncertain in North American orchards, farmers have been looking for other ways to help pollinate their crops. In this study, we looked at whether adding blue orchard bees, along with managed honey bees, could improve the pollination of sweet cherries and pears in Washington orchards. We released blue orchard bees into orchards where honey bees were already being used for pollination. We compared the results to orchards where only honey bees were used (three cherry and three pear orchards). We found that adding blue orchard bees increased the number of fruits that formed, but it didn't increase yeild. We also discovered that the blue orchard bees mostly visited the targeted orchard crop. In cherry orchards, more of the blue orchard bees stayed around (65%) compared to typical return (30 – 60%). However, in pear orchards, fewer bees stayed (17%). Our study shows that using both blue orchard bees and honey bees in Washington orchards can improve pollination, but it doesn't necessarily improve yields. Using multiple species of bee can be helpful when there aren't enough honey bee hives or when the weather isn't good for honey bee pollination.

Technical Abstract: Apis mellifera F. (honey bees) are the primary, global pollinators of spring orchard crops. However, due to high cost and uncertain availability of contracted migratory hive rentals in North American orchards, growers have been exploring alternative pollination options. Here we examine whether spring flying Osmia lignaria Say, the blue orchard bee, plus managed honey bees as co-pollinators enhance fruit set and yield in Washington sweet cherry and pear orchards. We released O. lignaria in orchard sites where honey bees were already added for pollination. We compared fruit set and yield at these sites to similar sites where only honey bees were present (three cherry and three pear sites). We found that within both orchards, the addition of O. lignaria significantly increased fruit set, but not yield. Using microscopic inspection of pollen grains taken from O. lignaria nesting provisions, we revealed the O. lignaria primarily visited the orchard flowers. Retention of O. lignaria in cherry orchards was slightly higher (65%) than historical O. lignaria retention in other orchard crops (30 – 60%). However, retention in pear orchards was significantly lower (17%). Our results show that adding O. lignaria to Washington spring orchard crops can increase overall pollination, but does not improve the fruit yield at harvest time. The strategy of using co-pollinators, O. lignaria and A. mellifera, in U.S. orchards may act as “pollination insurance” in years where A. mellifera hives are in low supply or when the weather is not amenable for A. mellifera flight activity during much of the bloom period.