Practices to enhance habitat of native bees, a key pollinator resource for almonds, citrus, and other crops, are worthwhile, especially when commercial honey bee colonies are in short supply.
Jessa Guisse, California pollinator outreach coordinator of the Xerces Society, explained that concept during a grower workshop in Tulare dealing with ways to provide food and shelter for native bees, butterflies, moths, and other species that pollinate crops and natural plants.
Guisse, who is based in Sacramento, worked in research on Osmia lignaria, also known as the blue orchard bee, a native bee pollinator of almonds, before taking her position with the society devoted to conservation of invertebrates in 2008. She has also worked with growers on hedgerows and other habitat improvements.
She coordinates programs with USDA’s Natural Resources Conservation Service (NRCS), local conservation districts, and University of California Cooperative Extension.
Seventy percent of the world’s plants need pollinators, she said, while 35 percent of the world’s crops depend on them. The value of U.S. crops that require pollinators ranges from $18 billion to $27 billion.
Among the some 4,000 species of native bees, some 1,400 species occur in California and include bumblebees, leafcutter bees, cactus bees, and sunflower bees. Although flies and others also move pollen about, bees are the most efficient, she said.
In California, almonds and other crops rely on European honey bee colonies rented from commercial beekeepers. Because of shortages due to diseases such as colony collapse disorder, colony rentals have risen from about $40 each in the mid-1990s to $150 and more in 2009. At two colonies per acre, the cost has growers looking for alternatives.
Although Guisse stated it is not likely to happen in California, she cited the severe shortage of bees in China, where 40 percent of the apple crop must be pollinated by hand, which would mean prohibitively high labor costs.
“So growers are looking for other means of pollination, and native bees can play an important role.”
Unfortunately, she added, native bees are also challenged by habitat loss and their lack of ability to develop resistance to pesticides as many other insect species do.
Guisse said native bees can perform a valuable function in making available honey bees more productive. In Yolo County, University of California researchers learned that sunflowers planted in alternating rows of male and female plants for hybrid production were visited by honey bee workers moving down one row at a time.
But where native bees, which move between flowers at random, were present, the seed-set more than doubled because the honey bees also switched rows when encountering native bees.
In cherry tomatoes, production gains were seen through better pollination by native bees which can shake loose pollen from deep in the blossoms, while honey bees cannot.
In making initial changes to improve native pollinator habitat, Guisse said growers can follow some general principles.
First, they need to identify native pollinator species in their area and look for topography and vegetation that will support them. These include riparian buffers with a diversity of flowering native plants, augmented by clovers and leafy crops left to bolt to provide nectar and pollen in the spring, to bring pollinators to strength when crops set blossoms.
Hedgerows or windbreaks with a variety of native plants can offer food sources for some pollinators, while snags, fallow ground, and mounds of earth for natural nesting sites sustain others.
Native bees do not build wax structures like honey bees. Instead they need nesting sites, according to species. Wood nesting bees, a solitary species, seek soft-pithed twigs or beetle tunnels in standing dead trees. They also can use bee blocks built for them.
Ground-nesting bees build nest tunnels under bare ground. Cavity-nesting species, such as bumble bees, nest in abandoned rodent burrows.
Once flowering plants and nesting sites are determined, it is important to protect them from disturbances and use of pesticides that could harm the pollinators. Insecticides can kill bees outright, but herbicides and even some fungicides can also be harmful.
As with honey bees, care should be taken to apply spray materials during early evening when native bees are inactive. Even when crops are not in bloom, the pollinators can be harmed by chemical drift near wild flowering plants.
Materials detailing wildlife habitat enhancement, including farm bill cost-share, incentive programs, are available through local NRCS and conservation district offices.
Shannon Mueller, Fresno County farm advisor, gave the workshop a historical account of European honey bees from their introduction in the 1800s to the critical state of their availability today.
Already weakened by invasive parasitic mites carrying viral diseases, the U.S. honey bee industry is coping with colony collapse disorder, which has inflicted up to 35 percent losses in colonies. The causes of CCD are obscure, but researchers suspect several factors contribute to it.
“It’s getting lots of media attention and there are lots of questions about it. It’s characterized by the disappearance of adult worker bees. The queens, young bees, and brood remain with pollen and honey inside colonies,” Mueller said.
One possible cause is the increased stress and shared infections brought about by shipment of bees over longer distances as a result of shortages and escalating rental fees attracting more distant beekeepers.
Other possibilities are drought, an accumulation of stress from mite infestations, direct or indirect consequences of pesticide use, or some change in the environment.
Researchers are also pursuing answers to why incidence of CCD is more one year than the next, suggesting it may be cyclical.
Mueller said beekeepers are responding with increased colony sanitation, replacement of queens, and additional research in bee nutrition.
Beekeeping itself is shrinking. The U.S. industry has an estimated 2.4 million colonies, or about half the number it had in 1945. Meanwhile, members are aging and fewer new beekeepers are entering the occupation.