Integrated Pest Management Guide

POLLINATORS AND THEIR PROTECTION

The cranberry flower is specialized for insect pollination. The petals reflex backward to expose the reproductive parts: a single pistil and a ring of eight stamens each with a basal anther sac and a long appendage ending in a terminal pore. Because of this floral morphology and the fact that cranberry pollen is heavy and sticky, bees are the primary cranberry pollinators and wind is not involved. For fruit set to occur, cranberry flowers require only a small amount of pollen to be deposited on the stigma. When more pollen is deposited on the stigma, more seeds will result. The more seeds a berry has, the larger it will be. Poor pollen transfer has a direct negative effect on fruit size and crop yield. Bumble bees and honey bees are the main pollinators of cranberry.

BUMBLE BEE ( HYMENOPTERA: APIDAE)

Bumble bees are the most important native pollinators of cranberries in British Columbia. Two studies done in the early 1980's in the Fraser Valley found that the most common bumble bee species on cranberry were Bombus mixtus Cress., B. terricola Kirby, and B. occidentalis Greene (Winston and Graf, 1982; MacKenzie and Winston, 1984) (Note: terricola and occidentalis are considered the same species by some and separate species by others). Bumble bees are robust, hairy bees with black, white and yellow and/or orange markings. These colours serve as warning signals indicating distastefulness and possession of a defense mechanism for animals that might otherwise prey on the bees. Unlike honey bees, bumble bees can sting repeatedly without losing the stinger as it has no barbs and does not become embedded in the enemy.

Bumble bees forage for both nectar and pollen on cranberry, usually simultaneously. To collect pollen, they hold onto the flower with their legs and vibrate their wing muscles, causing the release of a cloud of pollen that sticks to the hair on the bee's ventral surface. When the stigma of a flower touches pollen that has accumulated on the bee's body, pollen transfer occurs. Pollen transfer also takes place while the bee is collecting only nectar. Bumble bees remove pollen from the body hair by brushing the hindlegs over the body, collecting it in special indentations on the hindlegs called pollen baskets. The pollen is transported back to the nest in pollen baskets.

Bumble bees are social insects and build their nests in the ground, often in abandoned mouse burrows, empty bird nests, and even in other insulating materials such as discarded mattresses, manure piles and the walls of old buildings. The mated queen overwinters in the soil while the rest of the colony dies at the onset of cold weather. In the early spring, she establishes a new nest and rears the first worker brood. These workers are small sterile females that enlarge the nest, forage and tend to the next generation of workers which, due to conditions within the nest such as increased temperature, cell size, and food availability, are also larger. In late summer, males (called drones) and fertile females, next year's queens, are produced. The sole function of the drones is to fertilize the queens before dying in the fall.
 

Bumble bee

HONEY BEE ( HYMENOPTERA: APIDAE)

Apis mellifera, the only honey bee species in North America, is valued for the honey it produces. Honey bees forage on cranberry mostly for nectar. They harvest pollen by drumming the anthers of cranberry blossoms with their forelegs which causes pollen to be released.

Like bumble bees, honey bees are social insects. Honey bees build nests in which both workers and the queen overwinter. In contrast to the bumble bee, the honey bee queen requires the help of the sterile female workers. When a colony gets too large, a swarm consisting of the old queen and many workers will leave the hive to find a new home, leaving a new queen and the remaining worker population in the old colony.

Females develop out of fertilized eggs, while drones are produced from unfertilized eggs. Larvae are fed a mixture of glandular secretions and pollen. A queen is produced when young female larvae are fed only these gladular secretions, often called royal jelly, in greater amounts than that fed to worker larvae. This will happen when the colony is getting ready to swarm or when the old queen is aging. A queen lives up to 5 years during which time she continues laying eggs, her only activity in the hive. Workers carry out all the duties required by the colony. Honey bees have a caste system in which the youngest bees perform the most menial tasks while the responsibilities and the importance of the work, for instance the rearing of the brood, increases with the bee's age and experience. Due to their complicated communication system, bees are able to inform their fellow workers of the exact locations of food sources.

A colony can sometimes consist of more than 80,000 individuals, although colonies consisting of 30,000 to 40,000 are more common. New queens emerge in late spring or early summer. The drones mate with these new queens and then die. Unmated drones are either starved to death or killed by the workers in late summer or early fall. Honey bees prefer other forage to cranberries. Blackberries, false dandelion and clover are very attractive to honey bees and thus compete with cranberries for honey bee pollination.
 

Honey bee

RENTING HONEY BEES

Because bumble bees and other native bees are not present in sufficient numbers to pollinate commercial cranberry plantings, managed honey bees are important for berry production.

For pollination of commercial cranberries, place bee hives near the beds at 10 to 20% bloom. One to two colonies (hives) per acre (two to three per ha) is recommended. Because blooming weeds, especially brambles, will attract honey bees away from the cranberries, it is a good practice during bloom to mow or remove weeds if possible. Hives should be removed after cranberry bloom has finished.

COMPARING HONEY BEES TO BUMBLE BEES

Bumble bees are more consistent foragers for cranberry pollen than honey bees, which tend to forage more for nectar due to the great demand in the hive. "In field observations, on average 74% of the bumble bees collected pollen compared with only 3% of the honeybees" (MacKenzie,1994). Honey bees are able to collect cranberry nectar without contacting the stigma and, therefore, without transferring pollen. Bumble bees are faster foragers than honey bees. Bumble bees also visit more blossoms per minute than honey bees. Bumble bees work longer hours than honey bees, and continue foraging in cool weather or light rain. Bumble bees deposit more cranberry pollen and carry purer pollen to a stigma than do honey bees.

It has been estimated that two pollen collecting honey bees equal one bumble bee based on working rate and a 30% longer working day for bumble bees (MacFarlane and Patten, 1994). On a favorable 10-hour day in this study, one bumble bee visited 6,000 flowers. Eighty percent of honey bee foraging occurred between 11 am and 4 pm, while 85% of bumble bees foraged between 10 am and 7 pm. Honey bees have a more extensive foraging range than bumble bees and honey bees communicate within the hive about the quality of food sources while bumble bees learn from actually sampling the flowers.

OTHER BEE POLLINATORS

The alfalfa leafcutting bee, Megachile rotundata F., is a species of solitary bee in which each female is a reproductive that looks after her own young. It nests in tunnels above ground so it is possible to construct artificial nests and develop management strategies for this bee. Alfalfa leafcutting bees are managed extensively in Western Canada and the U.S.A. This bee has a number of potential advantages over honey bees. It has a limited flight range and foraging range so tends to stay where it is put. It is not aggressive, all females forage for both pollen and nectar, and management techniques are well developed and relatively easy.

More research is being done in New Jersey, Nova Scotia and Wisconsin to determine the economic usefulness of these bees in commercial beds. However, alfalfa leafcutting bees require brighter days with warmer temperatures than bumble bees and honey bees, so it may not be well suited for cranberry production in British Columbia.

There are many other species of solitary bees in the Fraser Valley, but very few individuals of these species are found in managed cranberry beds (MacKenzie and Winston, 1984). Many solitary bees specialize on plant species not found on cranberry farms. Solitary bees in other growing areas nest in bare patches and among vines right on the cranberry bed. Pesticide use on cranberry farms, competition with honey bees and habitat loss probably reduce the survival and reproduction of solitary bees.
 

Alfalfa leafcutting bee (photo courtesy of K. MacKenzie)	Alfalfa leafcutting bee (photo courtesy of  S. Marshall)

ENCOURAGING BUMBLE BEES

Encouraging bumble bees to establish on cranberry farms will contribute to better pollination of cranberry flowers. Bumble bees store only enough food reserves to keep the colony going for a few days. Therefore, improving the sequence of flower sources around cranberry bogs is considered the leading way to maximize residential populations of bumble bees. Bumble bees nest only where there is an ample food source early in the spring, and there is a heavy requirement for resources during reproductive production in the summer. Providing a sequence of flower sources around cranberry beds during these times will sustain and encourage residential populations of bumble bees. A succession of perennial plants like winter blooming heather ( Erica carnea and E. darleyensis) covering the early spring period, followed by varieties of Rhododendron that flower in March and April plus later-flowering trees (plum, cherry, crabapple) can be planted in small area close to beds. After cranberry bloom, forage plants are also needed because bumble bee colonies continue to grow and produce queens and drones in early to mid-summer. After mating, the new queens feed to build up their fat for overwintering. When lots of nectar and pollen sources are available, there is a good chance that a large population of queens will overwinter. Providing off-bog pollen and nectar sources that flower in July and August, such as cultivars of white clover or blooming heather (E. cinera), is also very important.

Note: Plants that enhance bumble bee foraging and survival may also attract honey bees away from cranberries. We suggest that you consider carefully the role of each type of pollinator on your farm before planting perennials for bumble bees. In this regard it may be helpful to consult with your beekeeper.

Most bumble bees nest in the ground, often in deserted mouse nests, or other dry and sheltered sites. On cranberry farms, bumble bee nests have been found at flood level on dykes bordering beds. High spring rain is detrimental to residential bumble bee populations because nests can be flooded and limited foraging time can lead to starvation. Nest boxes may be used to encourage bumble bees to nest near cranberry beds in the spring. These are wooden boxes the size of a large shoe box with an overlapping lid to keep bees dry, a small entrance hole, and a filling of upholster's cotton, pink wall insulation or bulk wool. While B. occidentalis prefers surface or underground hives, B. mixtus uses aerial waterproofed hives. Deer mice are enemies of surface colonies. Ants and wasps can establish colonies within the boxes. Nest boxes should be placed above the upper limit of the water table where they will stay dry. Another good idea is to locate nest boxes near a prominent feature such as a fence post or on a high point of land as this aids the bumble bees in orienting to their home. Place hives near attractive flower sources in early spring before queens start flying and before nest initiation. Each new queen digs a small cell in the soil for winter hibernation, and is likely to return to the natal nest site the following year to begin searching for a nest. After bee activity finishes (workers and old queen die) in the late fall, boxes should be collected, cleaned with a diluted bleach solution and stored until next spring.

PROTECTING BEES

Most organophosphate (e.g., diazinon, parathion, malathion, acephate, phosmet) and carbamate (e.g., carbaryl) insecticides used to control second-generation blackheaded fireworm larvae are highly toxic to bees. It is recommended not to apply any of them during blossom or within 7 days of the introduction of honey bees.

"Do not move hives back into parathion-treated fields until at least 36 hours after the application. Our tests have shown that about 90 percent of the killing of bees by parathion occurs during the first 24 hours after application" (Mayer and Johansen 1999). If for some reason insecticides are needed during bloom, select an insecticide of lowest toxicity to bees, and apply it in the evening after bee activity has ceased for the day. Studies in Long Beach, Washington, demonstrated that 80% of honey bee cranberry foraging occurred between 11 am and 4 pm while 85% of bumble bees forage between 10 am and 7 pm (MacFarlane and Patten 1994). Do not treat during warm evenings when honey bees are clustered on the outside of the hive and bumble bees are likely to continue foraging, especially if it is at all light. If an insecticide must be applied, spray at night then irrigate in the morning until bees start flying to flush insecticide from the foliage. This practice will minimize but not eliminate bee kill. Honey bees in hives have to be protected from insecticide application, as do bumble bees and other indigenous bees nesting and foraging naturally in cranberry fields. Bumble bees forage only 277 - 460 metres (300 - 500 yards) from their nesting sites, and solitary bees may be found nesting right in the beds. Growers should also continue to use caution if applying insecticides in late summer, because any bumble bees still foraging on late blooming cranberries or flowering weeds in the bog will be killed. Remember to respect the pre-harvest interval when applying any pesticide.

PESTICIDE IMPACT AND BEE POISONING

The following information was summarized from Mayer and Johansen (1999).

Insecticide applications to cranberry fields have an impact on native bees by reducing their abundance and the diversity of the species. Insecticide sprays during pollination also have damaging affects on managed honey bee colonies.

Bees are poisoned when they touch contaminated foliage, flowers, or water, and/or when they collect contaminated pollen or nectar. One honey bee forager returning to the hive with a load of contaminated pollen or nectar can cause extreme agitation and death of a number of bees including larvae. Several such foragers can seriously disrupt and damage the colony. Bees have been observed performing abnormal communication dances on the horizontal landing board at the hive entrance while under the influence of insecticide poisoning.

The most common symptom of bee poisoning is the appearance of excessive numbers of dead bees in front of the hives. Aggressiveness in bees may be caused by organophosphate insecticides. Stupefaction, paralysis, and abnormal activities of bees are commonly caused by organophosphate insecticides.

References cited in this chapter:

MacFarlane, R.P. and K.D. Patten. 1994. Cranberry pollination and Pacific Northwest pollinators. Washington State University Annual Report to the Cranberry Institute.

MacKenzie, K. E.and M. L Winston. 1984. Diversity and abundance of native bee pollinators on berry crops and natural vegetation in the Lower Fraser Valley, British Columbia. The Canadian Entomologist 116: 965-974.

MacKenzie, K. E. 1994. The foraging behavior of honey bees (Apis mellifera L.) and bumble bees (Bombus spp.) on cranberry (Vaccinium macrocarpon Ait). Apidologie 25: 375-383.

Mayer, D. F. and C. A. Johansen. 1999. Protecting bees from pesticides; pages 20-22 in Pacific Northwest Insect Control Handbook © Oregon State University. Available from Extension Services of Oregon State University, Washington State University and the University of Idaho.

Winston, M. L. and L. H. Graf. 1982. Native bee pollinators of berry crops in the Fraser Valley of British Columbia. Journal of the Entomological Society of British Columbia 79: 14-19.

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