Andrena on apple blossom. Photo: David Biddinger
A recent study involving a broad range of crops found that visitation by wild bees significantly improved fruit set whether or not honey bees were abundant in fields. On a bee-per-bee basis, wild bees can be more effective pollinators than honey bees, meaning they do not need to be as abundant as honey bees in order provide quality pollination.
Wild bees that fly in the early spring are better adapted for flying under poor weather conditions than most other bees. They visit flowers and pollinate in cool and cloudy conditions when honey bees are less active. In warm, sunny weather, wild bees often begin foraging earlier in the morning and fly later into the afternoon. Supporting a diversity of bees has advantages over relying on a single species (such as the honey bee) to provide stable pollination. If bee diversity is high in an orchard, when populations of one or several species fluctuate due to parasites or disease, other species continue to provide stable pollination.
Encouraging bee diversity
By encouraging wild bee diversity, growers can benefit from wild bee contributions to orchard pollination. Ongoing research at Penn State has shown the foraging ranges of most wild bees other than bumble bees is limited to only about 100 yards from nesting habitat. Bumble bees fly much farther, but they are limited in early season fruit crops to only a relatively few overwintering queens that have not yet begun to reproduce workers. So far this research has also shown that wild bees are still almost exclusively nesting in fence-rows, woodlots, and other un-managed habitat adjacent to orchards, but not in the orchards themselves, probably due to pesticides.
Smaller Pennsylvania orchards of 10 acres situated on the sides of mountains where they are surrounded by woodlots, are probably close to ideal for pollination by wild bees. In these landscape situations, if pesticides are managed for pollinators, wild bees can provide most if not all the pollination an orchard needs. For larger blocks or for orchards surrounded by other crops with no habitat, pollinator strips of wildflowers with supplemental nesting materials should be used as "stepping stones" for bees to move in from suitable habitat nearby or honey bees can be used to fill in pollination gaps due to distance.
At least 120 species of wild native bees can be found in fruit orchards during the growing season, according to surveys conducted by Penn State, Cornell University, and the Pennsylvania Department of Agriculture. Most of these bees live solitary lives. Each female works alone to build her small nest and to provide provisions so her offspring have plenty to eat while they grow. Most of the bees in orchards are ground-nesting bees, digging slender tunnels underground in which they build cells for each egg and its provisions. Many prefer to nest in bare patches of well-drained soil, and some will line nest cells with a waxy substance to protect their offspring from fluctuating soil moisture levels.
Andrena spp. are important pollinators in orchards and are often out for only several weeks in the spring.
Colletes spp., named for the waterproof cellophane-like substance they use to coat the inside of their nests, tend to nest in aggregations. While some people express concern over aggregations of ground-nesting bees, most bees are very docile and will not sting or defend their nest sites.
Lasioglossum spp., Halictus spp., Augochlorella spp., and more are a very diverse group; some species live solitary lives, while some nest in aggregations, and others form semisocial colonies where they live cooperatively with their sisters. They are referred to as "sweat bees" for their penchant to lap up salty sweat. Some species are a stunning bright metallic green, and others are tiny and dark.
Other bees common in orchards nest in tunnels, such as those made by boring beetles, or the bees may chew into the old growth of pithy stems to create their own tunnel. Some bees use materials such as mud, resin, and portions of leaves or flower petals to construct their nests.
Osmia spp. are among the most valuable tunnel-nesting bees in orchards. They use mud as partitions within their tunnel nests to separate individual cells and to seal nest entrances. Many mason bees will nest readily in artificial nest blocks constructed of reeds, bamboo, or small holes drilled into hard wood.
Small carpenter bees
Ceratina spp. are tiny blue-green metallic bees that excavate the old growth of pithy stems of shrubs such as raspberry, sumac, wild rose, or elderberry.
Large carpenter bees
Xylocopa virginica create their nests by chewing directly into hard wood. Over time, an accumulation of large carpenter bee nest tunnels may create structural issues in barns, picnic tables or decks, and so large carpenter bees are often considered pests. However, they can be effective pollinators of fruit trees.
Bombus spp. can be common visitors to flowers of tree fruits. Bumble bees are social bees that live in colonies founded by a queen. Worker bees, the daughters of the queen, help in nest building, brood-rearing, and defense of the nest. Queen bumble bees hibernate through the winter and initiate a nest in the early spring. Queens select an insulated cavity as a nest site, perhaps under clumps of bunch grass or in old rodent nest, and will forage widely to provision that nest. The queen will then remain in the nest and sit on her clump of eggs to keep them warm, similar to birds incubating their eggs.
Queen bumble bees are usually the only individuals that are active during the period when orchards are in bloom. One single queen bumble bee can be worth several hundred individual bumble bees over time, as a colony will grow in size through the spring and summer. In the fall, a new queen will be reared and the rest of the colony will die off when winter arrives.
Wild bee habitat
Research indicates that habitat near or on farms is the key to sustaining pollinators. Unlike honey bees, which can be moved around in hives, wild bees are fixed in the landscape and they need forage sources when the main crop is not in bloom. Many different species visit tree fruit flowers, but their flight/nesting periods extend significantly beyond the bloom time of the crop.
Flight periods of various bee groups extend before and after the bloom time of tree fruit crops. If no other flowering plants are near the orchard, the crop alone will not provide enough resources to support wild bee populations or boost the health of managed bees. If apple trees are the only blooming plants in the landscape, when apples are blooming, resources are plentiful, but bees go hungry before or after apple bloom.
Protect semi- or natural habitat such as woodlots, hedgerows, or field borders present on or adjacent to a farm. Supporting pollinators in orchards is a win-win situation. When habitat for pollinators is protected in or near orchards, wild bee populations are conserved and growers benefit from their fruit pollination. This protected habitat also supports populations of other beneficial insects--including those that prey on or parasitize orchard pests.
Simple strategies for pollinator conservation
Bees have two basic habitat needs:
- a diversity of flowering plants
- nesting sites
Additionally, there are a number of farm practices that can be adjusted to reduce bee mortality. The following are simple farm strategies for pollinator conservation.
Many native wildflowers will attract wild bees as well as managed bees, including milkweeds, wild hyssop, purple coneflower, bee balm, cupplant, prairie clovers, and New England aster. Planting wildflowers with overlapping bloom times will support pollinators from spring through fall.
Moisture-loving wildflowers like blazing star, boneset, or goldenrods can be planted in ditches or filter strips. Native flowering trees and shrubs such as willows, New Jersey tea, hawthorn, serviceberry, and spirea are also broadly attractive to pollinators and provide important early spring resources when little else is blooming in the landscape.
Nonnative and noninvasive annuals such as cosmos, buckwheat, and lacy phacelia attract bees and other beneficial insects and can be great options for a low-cost insectary field borders. Clovers or siberian squill can be planted in the understory of orchards. Use space creatively since even small plantings may be beneficial to pollinators.
In addition to requiring floral resources, pollinators need shelter (see table below). Many ground-nesting bees prefer to locate their nests in well-drained soil, often in small patches of exposed ground in sunny locations. Minimize deep soil tillage and the use of plastic mulch, as these can prevent bees from nesting in the ground. Leave snags or brush piles, along with undisturbed tall grassy areas, to provide nesting sites for tunnel-nesting bees as well as bumble bees.
Hedgerows, shelterbelts, and windbreaks containing native flowering trees and shrubs can offer multiple farm benefits. While helping to reduce erosion and provide screening, they also provide nesting habitat for bees as well as food. Nest habitat for mason beescan be supplemented by placing small wooden nesting blocks with drilled holes or small bundles of bamboo tubes throughout the farm.
Nesting habitat needs of wild bees and nest habitat supplementation techniques.
|Bee group||Species||Nesting sites||Nest habitat supplementation techniques|
|Ground-nesting bees||Cellophane bees, Dark sweat bees, Metallic sweat bees, Mining bees||Exposed patches of well-drained soils protected from compaction or tilling||Nesting sites are difficult to re-create, so protect existing nest sites and maintain patches of non-erodible bare ground; reduce tillage when possible|
|Tunnel-nesting bees||Mason bees, Large carpenter bees, Small carpenter bees||Snags and stumps with beetle borings, hollow plant stems, pithy stems||Maintain snags, brush piles; plant shrubs with pithy stems (e.g., cane berries, rose bushes, sumac)|
|Cavity-nesting bees||Bumble bees||Insulated cavities above or below ground, such as old rodent burrows or under grass thatch||Leave some tall, grassy areas unmown, leave brush piles|
Minimize pesticide use
Many insecticides and fungicides can be a general danger and harmful to managed bees, but they can have more serious impacts on wild bees particularly solitary bees that are solely responsible for finding a nest and providing for offspring. Wild bees reproduce more slowly than honey bees and cannot be moved out of the orchard so may be exposed throughout the season. Avoid use of highly toxic pesticides that are dangerous to bees when possible and do not use them on blooming plants or near areas of pollinator habitat.
Reduce direct exposure to bees by spraying in the evening (soon after dark) when pollinators are less active, and reduce drift by calibrating spray equipment. Alternatives to insecticides, such as kaolin clay pest barriers (like the product Surround), fruit bags, pheromone traps for specific pests, or crop rotation and diversity can help reduce pest outbreaks. Integrate different approaches for pest management, such as cultural and biological controls to keep insect pests and diseases below economic levels.
Other beneficial insects are also supported by the same features that support pollinators, and reducing the use of insecticides will likewise benefit predatory and parasitic insects that can help reduce crop pests. Keep in mind that bees are present in orchards before and after bloom and may even nest within orchard rows.
Technical and financial support for pollinator conservation
To help farmers create pollinator habitat, the USDA Natural Resources Conservation Service (NRCS) now offers technical and financial assistance for conservation practices such as establishing wildflower meadows, field borders, or hedgerow plantings. Programs such as the Environmental Quality Incentives Program (EQIP) and the Conservation Stewardship Program (CSP), among others, offer various opportunities to help growers meet conservation goals.
Visit the NRCS website for additional information about these and other programs, as well as contact information for NRCS offices.
The Xerces Society maintains an online database of pollinator conservation information, including publications from USDA and extension programs, and downloadable Xerces publications, such Farming for Bees, through the Pollinator Conservation Resource Center
Attracting Native Pollinators provides extensive background information and an identification guide to common native bees of North America along with chapters on native bee nest construction and habitat restoration.
Wild Pollinators of Eastern Apple Orchards and How to Conserve Them is available as a PDF free or in hard copy for purchase from the Northeastern IPM Center.