When was the last time you sighted a bumble bee? Photographed it?

It's National Pollinator Week and one of our favorite bumble bees is the yellow-faced bumble bee, Bombus vosnesenskii. It was also a favorite of internationally renowned bee expert Robbin Thorp, distinguished emeritus professor of entomology at the University of California, Davis, who passed away June 7 at age 85. (See obituary)

In fact, all bumble bees were his favorite, including the elusive Franklin's bumble bee, found only in a small range in southern Oregon and northern California and now feared extinct.  We remember a July 2010 interview with Thorp:

“People often ask the value of Franklin's bumble bee," Thorp told us. "In terms of a direct contribution to the grand scale of human economies, perhaps not much, but no one has measured its contribution in those terms. However, in the grand scheme of our planet and its environmental values, I would say it is priceless.”

“Loss of a species, especially a pollinator, diminishes our global environment,” he said. “Bumble bees provide an important ecological service--pollination. This service is critical to reproduction of a huge diversity of plants that in turn provide shelter, food (seeds, fruits) to diverse wildlife. The potential cascade of effects from the removal of even one localized pollinator may affect us directly and indirectly.”

Thorp treasured bumble bees and encouraged everyone else to do so, too.

The yellow-faced bumble bees are native to the west coast of North America, from Baja California to British Columbia. They're important pollinators, especially important for their buzz pollination of tomatoes, peppers and cranberries. Buzz pollination occurs when they grab a blossom and shake it, dislodging the pollen. Honey bees can't do that.

The Xerces Society for Invertebrate Conservation recently posted that one quarter (28 percent) of North American bumble bees are in some degree of extinction risk. "Bumble bees face many threats including habitat loss, disease, pesticide use, and climate change."  (See more information on bumble bees on the Xerces' site.)

Meanwhile, "across the pond," London has established a seven-mile long bee corridor of wildflowers just for pollinators.

"The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) said wild mammals had declined by 82 per cent since 1980, space for natural ecosystems had halved, and one million species were now at risk of extinction as a result of human action," according to a May 7, 2019 article in The Independent newspaper.  "Insect pollinators are vital for the maintenance of ecosystem health and for global food security. Insects are required to maintain the existence of 75 per cent of crop species, 35 per cent of global crop production and up to 88 per cent of flowering plant species," reporter Harry Cockburn wrote.

Want to learn more about the bumble bees around us? A good start is to read these two books, both co-authored by Thorp in his retirement:  Bumble Bees of North America: An Identification Guide (Princeton University, 2014) and California Bees and Blooms: A Guide for Gardeners and Naturalists (Heyday, 2014).

And, if you would like to get involved in citizen science, Bumble Bee Watch seeks your sightings.

Postdoctoral scholar Rosemary Malfi. (Photo by Kathy Keatley Garvey)

Especially when it comes to bumble bee colonies.

Postdoctoral scholar Rosemary Malfi of the Neal Williams lab, University of California, Davis, will speak on “Timing Is Everything: Bumble Bee Colony Performance in Response to Seasonal Variation in Resources” at 4:10 p.m., Wednesday, May 30 in 122 Briggs Hall.

“Wild bee populations are considered to be strongly regulated by the availability of flowering resources on which they rely for food, that is, pollen and nectar, yet we lack robust, experimental data demonstrating the mechanistic connections between the floral resource environment and bee population health," Malfi says. "The temporal distribution of resources, in particular, is an understudied but potentially highly influential aspect of habitat quality affecting bees. Bumble bees (Bombus spp.) are annual, euosocial insect with high conservation value. Because their colonies must grow for several weeks before reproducing the timing of within-season resource abundance and scarcity is especially likely to impact their demographic performance."

At her seminar, Malfi will describe her postdoctoral work here at UC Davis,  "in which we investigated the importance of the timing of floral resource abundance for bumble bee (Bombus vosnesenkii) colony success through two large field experiments involving the manipulation of the food environment that colonies experienced. In the first study, we assessed how differences in the resource environment early in colony development affected both individual and colony level traits across the season using radio-frequency technology (RFID) and mark recapture methods. In the second study, we determine whether a pulse of food resources early in development, compared to a pulse delivered later during the 'pre-reproductive' phase, has a greater or similar impact on the peak size and reproduction of bumble bee colonies. We use a null method of exponential colony growth to explore whether resource pulses have persistent effects on colony growth after the pule itself has disappeared. Together these studies demonstrate that resource abundance early in development is critical for the success of bumble bee colonies, and this populations."

A native of Philadelphia, Rosemary received her bachelor of arts degree from Bryn Mawr College, an all-women's liberal arts school in the greater metro area, and worked two years at the Academy of Natural Sciences of Philadelphia as a lab manager for the in-house Patrick Center for Environmental Research.

Mali holds a doctorate in environmental science (ecology) from the University of Virginia in 2015 , studying with major professor T'ai Roulston.   She focused her doctoral research on the influence that flower (i.e. food) availability and parasitism have on bumble bee (Bombus spp.) population dynamics, and how risks associated with these factors vary among species within a community. In her work, integrating field observations, parasite analysis, colony manipulations, the use of radio frequency technology, and simulation modeling, she investigated these sources of environmental influence independently and interactively through studies that focus on bumble bee populations and environmental risks present in northern Virginia.

Among the bumble bee parasites Malfi has studied: Nosema bombi, a pathogenic fungus implicated in "the precipitous and rapid decline of several bumble bee species across North America." During her graduate studies, she became especially interested in the interaction between bumble bees and one of their parasitoids, the conopid fly. "Although the basic biology of this interaction has been described," she says, "little is currently known about the ecology of this host-parasitoid relationship, particularly in North America." Malfi discussed her work on the conopid fly at the January 2016 open house of the Bohart Museum of Entomology, UC Davis.

Malfi's postdoctoral position at UC Davis ends in September, and then she will be moving to Massachusetts with her family. She will be working in the lab of Lynn Adler at the University of Massachusetts, Amherst, to carry out research on the influence of diet on bumble bee colony development and health.

Career plans? "For now, my career plans are to continue pursuing research on wild bee population health," she says. "In my next position at UMass Amherst, I'll be focusing on how the diet of bumble bees may mediate the influence of pathogenic parasites on individual- and colony-level performance."