Here is a blue orchard bee, Osmia lignaria. Photo by Kathy Keatley Garvey

YOLO COUNTY, CA (MPG) – Lexie Martin and Abigail Lehner, two doctoral candidates in the University of California, Davis Department of Entomology and Nematology, presented their research at the Orchard Bee Association’s recent annual meeting at Woodinville, Washington.

Martin of the lab of community ecologist Rachel Vannette, professor and vice chair of the department, presented her talk on “A Sequence- and Lab-Based Approach to Investigate Chalkbrood Disease Infection across the Western Range of Blue Orchard Bees (Osmia lignaria)."

Lehner of the lab of Professor Neal Williams, pollination ecologist, discussed “What Three Years of Longitudinal Monitoring at Osmia Nests Have Revealed About Houdini Fly Parasitism." Lehner was also elected the Orchard Bee Association treasurer. 

This was their third year of giving presentations to the organization. 

Lexie Martin is a doctoral candidate in the University of California, Davis Department of Entomology and Nematology. Courtesy photo

In her talk, Martin said that “Pathogen infection is a significant contributor to mortality and decreased fitness in many bees. Though much research has been done to understand diseases in commercially-managed social bee species, much less has been done to understand infection in solitary bees.”

“In particular, there has been concern for spillover of diseases from managed bee species to wild bee species, which could lead to further population declines of our native bees,” Martin said.

“As a result,” Martin continued, “it is critical to understand the variation in pathogen strains that can infect solitary bees and if pathogen strains can jump between bee host-species. In this study, we use a multi-method approach to investigate one, the variation in chalkbrood strains present within deceased blue orchard bee larvae across their western range and two, how variable communities of chalkbrood impact infection in blue orchard bees.”

It is unknown how chalkbrood strains vary within blue orchard bees and more broadly across bee species, and which strains are infective in blue orchard bees, according to Martin, and this project will have a significant positive contribution to a broader understanding of bee disease dynamics.

In her talk, Lehner said that “The introduction of non-native species poses major risks in agriculture, with hundreds of new alien species recorded annually. Houdini flies (Cacoxenus indagator) were recently introduced to the United States and parasitize cavity-nesting native bees, including the blue orchard bee (Osmia lignaria), a managed solitary bee used to pollinate spring orchard trees.” 

Pictured is Abigail Lehner, a doctoral candidate in the University of California, Davis Department of Entomology and Nematology. Courtesy photo

“The introduction of Houdini flies poses an existential threat to the stability of the solitary bee industry, the livelihoods of orchard managers and to native bee population persistence,” Lehner said. “We have monitored parasitism rates at blue orchard bee nest blocks in Washington, Oregon, and California over three years to understand temporal patterns and long-term impacts of Houdini fly parasitism. We found Houdini fly parasitism rates significantly increased over three years in the Pacific Northwest. Overall, this research will inform commercial management and conservation strategies for cavity-nesting bees.”

Osmia lignaria, commonly known as the orchard mason bee or blue orchard bee, is among 4,000 native bee species in North America. It is a megachilid bee that nests in reeds and other tubelike natural structures. The bee pollinates almonds and blueberries, and a variety of stone fruits, including apples, pears, cherries, apricots and plums. 

Osmia is used commercially in agricultural operations, especially in almonds and early blooming-fruit trees, and occupies handcrafted "bee blocks." Considered efficient pollinators, they are able to forage in cooler temperatures than honeybees. Gardeners often set up "bee condos" or "bee hotels" for them in their landscapes.

The kleptoparasitic fly, Cacoxenus indagator, is a species of fruit fly native to central and southern Europe. The adult lays its eggs in the stored pollen of a mason bee's newly constructed nest.  The fly larvae feed mainly on stored pollen but can also eat the bee larvae. This fly is commonly known as the Houdini fly for its ability to escape through the cell’s mud wall. The small brown fly (wing length 2.5mm) has clear wings and large red eyes. 

The Orchard Bee Association was launched in 2011 by a team of independent businesses, orchard managers and researchers to accelerate the production and use of orchard mason bees (specifically, Osmia lignaria, O. cornifrons, O. cornuta and O. rufa) in various spring crops and orchards.