March – Native Bees
Barb Ogg, University of Nebraska – Extension Educator, shares her knowledge and expertise on insects that often are pest problems. This month, with help from Mary Jane Frogge and Soni Cochran, UNL Extension, she describes an insect that we shouldn’t consider a pest.
Encouraging Native Bee Pollinators
In the US, about 4,000 species of native bee pollinators have been identified. Because most of these bees do not live in a hive or colony, they often are overlooked. These bees collect pollen from flowering plants to feed their offspring and, in doing so, pollinate the plants they visit. They are more important pollinators today than ever before.
Native bees range in size from about 1/8- to more than 1-inch long. Coloration varies from dark brown or black to metallic green or blue; they may have stripes of red, white, orange, or yellow. Their names often reflect their nest building behaviors: plasterer bees, leafcutter bees, mason bees, digger bees, and carpenter bees.
Lifestyles. Bees can be divided into two groups by their lifestyles: solitary or social. The stereotypical image of a bee is one living in a hive, but only a few species of bees are social. Social bees share a nest and divide the work of building the nest, caring for the offspring, and foraging for pollen and nectar. The primary social bees are the honey bee (not native to the US) and the bumble bees (about 45 species in the US).
In contrast, most native pollinating bees – nearly 4,000 species in the U.S. – are solitary nesting bees. Each female creates and provisions her own nest, without cooperation with other bees. Although they may nest together in large numbers, the bees are only sharing a good nesting site. The photo to the left is of a leaf cutter bee that emerged from a stack of brood cells that were brought to the Lancaster County extension office last summer. The bee is about the same width as the brood cells. Females that emerge will find a deep hole about the width of their body, form a brood cell with a cut leaf circle and pack the cell with a pollen ball. After she lays an egg on the pollen ball, she seals off each cell and makes a new one.
Solitary bees are either stingless or very unlikely to sting.
Life Cycles Solitary bees. The life cycle of a solitary bee consists of four stages: egg, larva, pupa and adult. Adult bees build a brood cell, then collect pollen and form a pollen ball. The female lays an egg on the pollen ball and seals off the cell. The egg, which resembles a tiny white sausage, incubates for 1-3 weeks, then hatches into a white, soft-bodied, grub-like larva. The larva feeds on the pollen ball left in the cell by the mother bee. After feeding and growing quickly, the larva changes into a pupa. Within the pupal stage – which may last many months – the larva transforms into its adult bee form. When the adult bee emerges, it is ready to feed, mate, and continue the cycle.
About 30 percent of native bee species are wood-nesters. These species use the soft pithy centers of twigs or reeds, or holes in wood tunneled by wood-boring beetles. In the case of carpenter bees, the bees themselves create the tunnel in wood. Some other bee species tunnel into soft, above-ground rotting logs and stumps.
The other 70% of native bees nest underground. These bees tunnel into the soil and create small chambers – brood cells – under the surface.
Social bees. Bumble bees are important pollinators and are only native bees which are truly social. They live in colonies, share the work, and have overlapping generations throughout the spring, summer, and fall. However, unlike the non-native honey bee – which survives through the winter – the bumble bee colony is seasonal. At the end of the summer only the fertilized queens survive to hibernate through the winter. In the spring, she does not use the nest she grew up in, but searches for a new nest.
Bumble bees usually nest in the soil – an abandoned rodent burrow is a favorite location. The queen creates the first few brood cells out of wax she produces, and then provisions these cells with pollen and nectar and lays eggs. Bumble bees differ from solitary bees when feeding their larvae. They provide food gradually, adding it to the brood cells as the larvae need it – called progressive provisioning – rather than leaving all the food in the cell before laying the egg. In addition, bumble bees make a small amount of honey, just enough to feed the colony for a few days during bad weather.
It takes about a month for the queen to raise the first brood. When they emerge, these bees become workers – foraging and tending the growing number of brood cells. The queen will continue to lay eggs, so the colony will grow steadily through the summer. At the end of summer, new queens and drones will emerge and mate. As temperatures drop, the old bees, including the old queen, will die, leaving only the new, mated queens to overwinter.
Increase Pollinators in Your Landscape.
Pollinators require somewhere to nest and flowers from which to gather nectar and pollen. Three things you can do to enhance pollinators in your garden are: provide a range of native flowering plants that bloom throughout the growing season, create nest sites for native bees, and avoid using pesticides.
Plants for Food.
You can increase the number of pollinators in your area with a few simple additions to your landscape. Native plants are the best source of food for native pollinators, because plants and their pollinators have co-evolved, but many varieties of garden plants are also good.
Plant flowers in groups or mass plantings to increase pollination efficiency. Consider the bloom season to provide food from early spring to late fall. Many herbs and annuals, although not native, are very good for pollinators. Mint, dill, oregano, chives, and parsley are a few herbs you can plant. Zinnia, cosmos, and sunflowers are excellent annual flowers that attract bees and butterflies. Even weeds like common milkweed can be a source of food for pollinators. Consider plants that are suitable for the larval stages of pollinators, like butterflies. Here’s a table of plants to consider for attracting native bees to your Nebraska acreage.
Wood-Nesting and Cavity Nesting Bees.
Nesting blocks. You can make a bee block by drilling nesting holes between 3/32″ and 3/8″ in diameter, at approximate 3/4″ centers, into the side of a block of preservative-free lumber. A variety of hole sizes will attract different-sized pollinators. The holes must be very smooth inside and closed at one end. The height of the nest block isn’t terribly important – 8″ or more is good – but the depth of the holes is. Holes less than 1/4″ diameter should be about 3 – 4″ deep. Holes 1/4″ or larger should be 5 – 6″ deep. Nesting blocks should be placed in the landscape early to make sure it is there when the bee needs it. If you have a bee-filled block from last year, don’t clean it out until after the bees have emerged. You might want to add a second clean block for this year’s brood, leaving the old one until all the bees are emerged.
Logs and snags. Get some logs or old stumps and place them in sunny areas. Those with beetle tunnels are ideal. Plant a few upright, like dead trees to ensure some deadwood habitat stays dry. On the southeast side of each log, drill a range of holes, as outlined above.
Stem or tube bundles. Some plants, like bamboo and reeds have naturally hollow stems. Cut the stems into 6-8″ lengths. Be careful to cut the stems close to a stem not to create a tube with one end closed. Fifteen to twenty stem pieces tied into a bundle with all the stem ends closed on the same end makes a good nest. You can also make a wooden frame to hold as many stems as you fit inside.
Nest Location. The location of the nest is important. Nests should be placed in a sheltered location to protect them against severe weather, with the entrance holes facing east or southeast to get morning sun. Any height will work, but 3-6 feet is convenient. With stem bundles, make sure the stems are horizontal. Place them on a building, fence, stake, or in a tree. Make sure you fix them firmly so they don’t shake in the wind.
Ground Nesting Bees. If you have a large acreage you may be able to provide bare or patchy soil for ground-nesting bees. Simply clear the vegetation from some small patches of level or sloping ground and gently compact the soil surface. A south-facing slope is good. Different ground conditions – from sloping banks to flat ground – will draw different bee species.
Water. A clean reliable source of water is essential for pollinators. Water features such as bird baths and small ponds provide drinking and bathing opportunities for pollinators. Water sources should be shallow or have sloping sides so pollinators can easily approach the water without drowning.
No Pesticides. To protect pollinators, pesticide use must be avoided. This can be difficult for gardeners who have well manicured landscapes. Here are some tips to help you ease into a pesticide-free environment. * For natural pest control provide a diverse garden habitat with a variety of plant sizes, heights and types to encourage beneficial insects. * Lower expectations and accept a little bit of pest activity. * Remove garden pests by hand.
Sources: The Xerces Society, a nonprofit organization that protects wildlife through the conservation of invertebrates and their habitat.
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