Woodland Fish & Wildlife • 2020 Forest Bee Pollinators Author: Christine Buhl, Ph.D., Oregon Department of Forestry (ODF) Entomologist Introduction Bees In Forests native bees. These forested ecosystems offer forage and a place to make nests Often, our first thought of pollinators In the Pacific Northwest (PNW) alone, or hibernate. A variety of understory usually takes us to honey bees in agricul- over 500 species of bees have been forbs and woody shrubs as well as some ture. Honey bees play such a large role identified with an estimated 300 more broadleaf trees provide nectar and in agriculture that sometimes the many awaiting formal description (Stephen et pollen. Exposed soil and woody debris wild bees that occur in other habitats such al. 1969). Despite having so many bees, provide space for nesting, and cavities as forests are overlooked. There are over we know surprisingly little about which such as old rodent nests provide refuge 4,000 known species of wild bees in North bees occur where and in what abun- during periods of hibernation. The types America (O’Toole 1991), many of which dance. Even less is known about the bees of bees found in forests vary depending occur in temperate forest ecosystems. that utilize forest habitats (Rivers et al. on the microclimate (temperature, light, While this publication focuses on bees, 2018a). Relationships between wild bees moisture, etc.), as well as the availability there are also many other important and forest ecosystems are better studied of preferred forage and nesting materi- insect and non-insect animals that serve in the tropics; but in temperate forests, als. As such, bee communities will vary as pollinators. where most trees are wind-pollinated, for different levels of forest manage- bees have been largely ignored. New ment – meaning that bee communities research in PNW forests indicates high found in clearcuts will differ from those bee abundance and diversity, even in found in closed-canopy young forests or intensively managed forests (Rivers et late successional forests. al. 2018b) or forests damaged by wildfire (Galbraith et al. 2019). Forests are a Major disturbances such as logging great place to find certain species of and wildfire mimic early successional Bumble bee (Bombus sp.) visting waterleaf (Hydrophyllum sp.) in Oregon west side forest. C. Buhl, ODF Sweat bee (Augochlorella sp.) visiting Bumble bee (Bombus sp.) visting inside- Mason bee (Osmia sp.) visting lupine native hawkweed (Heracium sp.) along a out flower (Vancouveria sp.) in Oregon (Lupinus sp.) in recently logged Oregon forest road. C. Buhl, ODF west side forest. C. Buhl, ODF east side forest. C. Buhl, ODF 1 Woodland Fish & Wildlife • 2020 Bee Life History Bee life history is highly variable among bees as a collective group. Some bees such as bumble bees are highly euso- cial, while others such as mason bees tend to be more solitary. However, this is a generalization and it should be noted that variations in social behavior occur even among species within the same genera. Eusocial bees include honey bees and bumble bees and some species of sweat and carpenter bees. Much of what we know about bees is from honey bees. Honey bees are a special case because they are ‘managed bees’, meaning that we augment their life history by Bee forage (Pedicularis sp.) in the forest. Mining bee (Andrenidae) emerging from maintaining them in unnaturally large C. Buhl, ODF ground nest C. Buhl, ODF numbers within man-made hives and provide some amount of care to gain forest dynamics. Disturbance increases their service as crop pollinators and abundance and diversity of many bee honey producers. In the wild, honey species (Galbraith et al. 2019, Hanula bees nest in much smaller numbers et al. 2015) by: 1) exposing bare soil and in cavities such as tree abscesses. for ground-nesting bees and germina- The life history of honey bees is widely tion of forage plants, 2) increasing both known, but in North America these light availability for forage plants and bees represent just one species - Apis thermal environments for bee nests, and mellifera; despite there being 20,000 3) leaving behind pithy (soft and easily known species of bees worldwide! excavated) stems and woody debris for All bees develop from eggs into larvae, nesting. It may be surprising to know pupae, and then adults. But from here, that the majority of wild bees nest in the life history varies widely often due to ground or in cavities of various materials. sociality. Only 10% of bee species are Exposed loose or hard-packed loam, eusocial (UC Berkley Bee Lab). Eusocial sand, or rocky soil is utilized by a variety bees live and work together to raise a of bee species for nesting. Wood-nesting colony of individuals that are divided bees bore into wood or utilize existing among castes. A colony consists of a cavities made by woodpeckers, wood- queen bee, female worker bees, and boring beetles, or natural decay. Other male drone bees. The queen produces bees rely on the pithy stems of various unfertilized eggs, which become drones, herbaceous or woody plants for their Ground nest. Sarina Jepsen, Xerces and fertilized eggs, which develop into nests. Although shallow ground nests workers and additional queens that and nests in aboveground materials may eventually leave to form their own be consumed by fire, fires often move colonies. Workers forage for nectar and over the landscape quickly and may pollen, care for the brood, and maintain not have enough time to penetrate the and defend the colony. Drones mate soil of deeper nests (Cane 1991, Cane with the queen and then die. Without a and Neff 2011). Following severe fires, queen a colony would swiftly collapse. bees from adjacent areas often quickly In managed honey bee populations, a recolonize fire-damaged areas to take single queen may live for several years, advantage of newly available nesting but queens of wild populations of eusocial and foraging habitat. species live for a year or less. Non-queen Stem nest. Justin Wheeler, Xerces 2 Woodland Fish & Wildlife • 2020 castes live for weeks to months. In wild winter in a late larval resting phase before populations of eusocial bees, the colony pupating in the spring. Most solitary bee dies at the end of the season and only adults are active for 4-6 weeks during the mated queens live to overwinter. These blooming season. Production of brood in queens then emerge in spring to nest solitary bees typically takes place over the and start a new colony. Eusocial bees course of weeks versus a span of months are often multivoltine meaning that for eusocial bees, during which fewer envi- they can produce multiple generations ronmental fluctuations may occur that can within the span of a year. impact solitary bee population numbers. An estimated 70% of bee species are Pollination solitary and nest in the ground and another 5% of solitary bees nest in stems (UC Bees are prized for the essential ecosys- Berkley Bee Lab). It is common for many tem service they provide as pollinators. solitary bees to occupy one location, Some plants can self-fertilize, while giving the appearance of communal living. others are pollinated by wind, or water. However, these solitary bees are not However, many plants require the aid of working together but simply aggregat- animals to transfer pollen. Across the ing, in separate nests, in a highly desirable globe many types of animals are capable area. Solitary bees have no colony or of pollination; among these are bats complex caste system. They lay individual and other mammals, birds, lizards, and Bee forage (Dodecatheon sp.) in the for- eggs, and young develop and overwinter various insects such as moths, butter- est C. Buhl, ODF in their individual cells. Most solitary bees flies, flies, beetles and of course bees. are univoltine, meaning that there is only Pollination is also provided passively by proportion of these pollination services one generation a year. They emerge as many other animals, often when pollen is provided by bees. An estimated 75% adults in the spring to mate and lay eggs sticks to their bodies as they move past of our crop plants (including feed for that become the next generation of brood. plants in their search for food or shelter. livestock) rely on bees for pollination Solitary bee eggs typically develop in less Of all the flowering plants worldwide, an (Klein et al. 2007). Pollination allows than 1 week, the hatched bees then spend estimated 90% are pollinated by animals plants to reproduce, maintains genetic 2-3 weeks as larvae. Some species over- (Ollerton et al. 2011). The largest variability, produces products for human consumption and commerce, and con- tributes to environmental aesthetics. In North America and elsewhere honey bees are known to be a pollination pow- erhouse although contributions by other bee species is becoming better realized (Ollerton et al. 2012). Although there are fossil records of honey bees species in North America that have long since become extinct, in the modern era, honey bees were not present in North America. Honey bees were brought from Europe by settlers to serve as generalist pollinators of many crops such as apples, melons, berries, nuts, and even cruciferous vegeta- bles such as broccoli and cabbage. Honey bees were not brought to the west coast until the 1860s (Kellar 2014), up until which time native, wild bees provided most of the pollination services. Wild bees often outnumber honey bees, and during a period of honey bee decline (2006-2011) Solitary bee life cycle. Sarah Scott, USGS due to colony collapse disorder, almond 3 Woodland Fish & Wildlife • 2019 Bee Declines In 2006 reports of large honey bee colony losses, mainly in the form of missing workers, suddenly spiked in North America and was termed ‘colony collapse disorder’.