CES - Pollination Tool Kit: Case Studies and Programs

Alfalfa Leafcutting Bee and Alfalfa Seed in the Pacific Northwest

The alfalfa leafcutting bee (Megachile rotundata) serves as a prolific and effective pollinator for the economically important alfalfa seed crop in western North America. Today, leafcutting bees are managed extensively in Washington, Oregon, Idaho, Montana, and Nevada. In 1990, over two billion managed leafcutting bees, with a value of $10.9 million, were used to produce alfalfa seed on 61,500 acres in the region — more than half the total national production (Peterson, Baird, and Bitner 1992). A single leafcutting bee is capable of pollinating enough flowers to produce 1/4 lb. of seed in a season (Johansen 1991).

The alfalfa leafcutting bee species was brought to North America from the European continent in the first half of the twentieth century. The advantage of using this species as a managed pollinator was soon recognized, and it did not take long for this bee species to become the preferred pollinator for the production of alfalfa seed in the Pacific Northwest. Leafcutting bees are ideal pollinators to produce alfalfa seed because: they prefer alfalfa to other plants when foraging; they are inclined to collect pollen to provision their nest, which results in rapid and efficient pollination of the crop; and they are both reliable and relatively easy to manage.

The management of leafcutting bees has proven to be both effective and profitable. In fact, alfalfa seed producers in California, where honeybees are the major pollinators, have expressed interest in using the leafcutting bee. Rising honeybee management costs due to recently introduced parasites, and the spread of Africanized honeybees, have made this option even more attractive. However, there are problems with the use of leafcutting bees. The greatest current concerns for leafcutting bee producers include potentially significant population losses as a result of pesticide poisoning, the spread of chalkbrood disease, parasitism, and predation (Peterson, Baird, and Bitner 1992).

The threat of pesticide poisonings has been a serious concern for producers of leafcutting bees since they began being managed as a pollinator of alfalfa seeds. Alfalfa pests, including lygus bugs, pea aphids, and the alfalfa weevil, require control during the pollination period. Until the early 1970s, it was not uncommon for alfalfa seed fields to be subjected to up to eight pesticide applications in a given season (Johansen and Eves 1973). Today, most growers use field scouting and action threshold methods when determining the frequency of applications. The initiation of an integrated pest management program for alfalfa seed has reduced the number of applications to less than three per season, dramatically lowering pollinator losses as a result (Peterson, Baird, and Bitner 1992).

Sources
Peterson, S.S., C.R. Baird, and R.M. Bitner. 1992. "Current Status of the Alfalfa Leafcutting Bee, Megachile rotundata, as a Pollinator of Alfalfa Seed" Bee Science 2: 135–142.

Johansen, C.A. 1991. "Introduction" in Alfalfa Seed Production and Pest Management. Western Regional Extension Publication 12.

Johansen, C.A., and J.D. Eves. 1973. "Development of a Pest Management Program on Alfalfa Grown for Seed" Environmental Entomology 2: 515–517.

Canadian Blueberry and Native Pollinators in Southern New Brunswick

Farmers in Eastern Canada rely heavily on approximately 70 species of native insects, including many species of bumblebees, to pollinate lowbush blueberries for commercial production. Between 1969 and 1978, fields adjacent to blueberry fields were sprayed with an organophosphorate insecticide (Fenitrothion) to reduce spruce budworm populations. Blueberry crop yields were dramatically lower beginning in 1970 and remained so throughout the decade. These lower crop yields coincided with significant reductions in the population of native bumblebees (Kevan 1975a).

Peter Kevan conducted a study to examine the link between these two trends. He found that the insecticide spray program was responsible for the reduced pollinator populations and, consequently, the lower blueberry crop yields. This conclusion was based on the observation that reduced populations of native bees had been noticed only since and where Fenitrothion had been sprayed. In addition, dead or debilitated bumblebees collected from fields suspected of contamination did indeed have Fenitrothion in their tissues (Kevan 1975a). Native bees recovered steadily after Fenitrothion was replaced with a narrower spectrum insecticide (Kearns, Inouye, and Waser 1998).

Sources
Kearns, C.A., D.W. Inouye, and N. Waser. 1998. "Endangered Mutualisms: The Conservation of Plant-Pollinator Interactions" Annual Review of Ecology and Systematics 29: 83–112.

Kevan, P.G. 1975. "Forest Application of the Insecticide Fenitrothion and its Effect on Wild Bee Pollinators of Lowbush Blueberries in Southern New Brunswick, Canada" Biological Conservation 7: 301–309.

Kevan, P.G. 1975a. "Pollination and Environmental Conservation" Environmental Conservation 2(4): 293–297.

Invasion of Africanized Honeybees to North America

In 1956, apiculturist Warwick Kerr introduced the African honeybee (Apis mellifera scutellata) to the southeastern coast of Brazil. He wanted to breed, in a controlled environment, a more productive honeybee that was better suited than the European honeybee for the Neotropical climate. One year after their introduction, 26 queen bees were accidentally released into the forest. They have since gradually spread throughout Latin America, moving northward between 200 and 300 miles each year. In 1990, the first one was reported in the United States in southern Texas. They are currently found throughout the American southwest and continue to spread at an increased pace of 375 miles per year (Kunzmann et al. 1995).

The African and European honeybees are nearly identical species. They share similar biochemistry, genetics, diet, and social behaviors. For humans, the most significant trait that separates these two subspecies is the African honeybee's aggressiveness. African honeybees respond to threats more quickly and in far greater numbers than their European counterpart. This makes the African honeybee, and European honeybee colonies invaded by African queens, more difficult to use as managed pollinators of agricultural crops. In 1993, more than sixty human fatalities due to stinging incidents were reported in Mexico. In addition to increased public health risks, the invasion of African honeybees to North America poses serious ecological consequences. Their aggressive nature and foraging strategies have led some scientists to believe that Africanized honeybees will out-compete many native pollinators for valuable forage resources (Kunzmann et al. 1995).

Due to its potential implications to agriculture, the expansion of African honeybees is currently monitored and researched extensively. However, the actual affect of the invasion and how far northward the African honeybees will spread is still not well known.

Source
Kunzmann, M.R., et al. 1995. "Africanized Bees in North America," in Our Living Resources, E. LaRoe, et al. eds., Washington, D.C.: U.S. Department of the Interior — National Biological Service, pp. 448–451.

Fig Trees and Fig Wasps in Tropical Forest Communities

Figs are a critical resource for both people and animals living in many tropical forest communities. In some areas, they may constitute as much as seventy percent of the diet of vertebrate species.

Most of the world's 750 fig species rely on wasps for pollination. In fact, most types of figs rely on a single species of wasp as their exclusive pollinator. In return, the wasps depend on developing fig seeds as a vital food source during an important period of their life cycle (Janzen 1979).

Figs are often considered a 'keystone' species because they are an essential component linking many organisms within an ecosystem. If fig populations are disrupted due to selective logging or other types of habitat fragmentation, the results could be disastrous. Such disruptions could trigger cascading extinctions of the multitude of species that depend on them, including primates and birds. The results could be equally devastating if the population of a fig tree's exclusive pollinator is disrupted by, for example, insecticide overspray (Bronstein 1992).

Judith Bronstein and her colleagues conducted a study of fig species and their pollinators in an attempt to determine the effects of fragmentation on sustainability. Their goal was to determine how many fig trees an area must retain to support a wasp population. They concluded that between 95 and 294 trees of one fig species would be necessary to support the survival of a pollinator population for at least four years. A related study by Doyle McKey determined that a minimum of 300 trees would be required to ensure the long-term sustainability of a population of fig wasps (Bronstein 1992). McKey also tried to determine "what area of forest must be preserved to ensure the maintenance of minimum viable populations of figs and wasps" (McKey 1989). He concluded that between 800 acres and 800 square miles of intact forest would be necessary to support the long-term sustainability of a specific species of fig tree, its pollinator, and all dependent fauna.

Sources
Bronstein, J.L. 1994. "The Plant-Pollinator Landscape," in Mosaic Landscapes and Ecological Processes, L. Hansson, I. Fahrig, and G. Merriam eds. London, U.K.: Chapman and Hall, pp. 256–288.

Bronstein, J.L. 1992. "Seed Predators as Mutualists: Ecology and Evolution of the Fig-Pollinator Interaction" in Insect-Plant Interactions, Vol. IV, E. Bernays ed. Boca Raton, FL: CRC Press, pp.1–44.

Buchmann, S.L., and G.P. Nabhan. 1996. The Forgotten Pollinators. Washington, D.C.: Island Press.

Janzen, D.H. 1979. "How to Be a Fig" Annual Review of Ecology and Systematics 10: 13–51.

McKey, D. 1989. "Population Biology of Figs: Applications for Conservation" Experencia 45: 661–673.

Nason, John D., E.A. Herre, and J.L. Hamrick. 1998. "The Breeding Structure of a Tropical Keystone Plant Resource" Nature 391: 685–687.

Wiebes, J.T. 1979. "Co-evolution of Figs and Their Insect Pollinators" Annual Review of Ecology and Systematics 10: 1–12.