Honey bee attractants are products designed to increase bee visitation to treated crops with the goal of increasing pollination, fruit-set, yield, and ultimately profits. These products are mixed with water and applied to crops with conventional spray equipment.
Several attractants have been marketed, and most have had a doubtful performance record. However, the situation may be improv- ing with recent advances in our understanding of pheromones– ‘exter- nal hormones’ that insects secrete to regulate the behaviour and physiology of other individual insects. Honey bees have a rich battery of pheromones. Synthesizing and manipulating these chemicals may give bee-keepers and crop growers important new tools for pollination.
In general, attractants are warranted only when conditions are suboptimal for pollination or when the crop is not attractive to bees.
The idea is to focus bees away from competing bloom, improve their
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efficiency when foraging conditions are poor, or to improve their effi- ciency when their numbers are low relative to the amount of bloom needing pollination. Some situations in which an attractant may be advisable are:
• A grower may apply attractant to the centre of a large field to increase bee visitation there if the bee-keeper was able to locate hives only on the periphery.
• An attractant may increase bee visitation in crops such as cranberry and pear that are known to be comparatively unattractive to bees.
• Attractant may help keep bees foraging in crops during times when natural nectar flows would otherwise lure them away. Most honey producers are aware of the natural nectar flows in their area. In a good working relationship, a bee-keeper can alert his client grower of the risk of competing plants and advise the use of an attractant.
• Attractant may be advisable when cool weather is discouraging bees from flying or when a late-season freeze has decreased the number of viable flowers.
• Attractant may help focus pollinators on the crop if a sudden period of warm weather has compressed bloom and the resulting number of flowers requiring pollination is nearly too much for the available bees.
Bee attractants encourage bee visitation, not necessarily bee polli- nation. If the flowers are not appealing to bees, no chemical attractant will make bees work them. Likewise, if there are no bees in the area, an attractant will not draw them in from great distances. A grower’s first priority must be the bees themselves.
Some products have been marketed which contain sugars, attrac- tive oils, or some components of Nasonov pheromone, a pheromone that bees use to orientate to nest sites and to low-odour resources such as water. Some trade names are Bee-Here®, Beeline®, Beelure®, Bee- Scent®, and Pollenaid®. The research support for these products is generally not strong, but more work is certainly warranted (Winston and Slessor, 1993). Sugar-based attractants are shown to actually diminish pollination efficiency because bees are diverted to collecting syrup off foliage instead of pollinating the flowers (Free, 1965).
Beelure®, a sugar-based product, does not increase bee visitation to apple blossoms (Rajotte and Fell, 1982). Clearly, future research should focus on pheromone-based products.
In a study by Mayer et al.(1989a) in Washington state, Bee-Scent®, a Nasonov pheromone-based attractant, increased honey bee visitation for 24 h post-treatment in ‘Red Delicious’ apple, ‘Van’ cherry, pear (‘Bartlett’ and ‘Bosc’), and ‘President’ plum. It did not increase visita- tion in ‘Anjou’ pear. In some orchards, bee visitation was elevated for Honey Bees: Managing Honey Bees for Pollination 59
72 h post-treatment. Bee-Scent®increased fruit-set by at least 23% in
‘Bartlett’ pear, by 44% in ‘Anjou’ pear, by 12% in ‘Van’ cherry, and by 5–22% in ‘Red Delicious’ apple. Bee-Scent Plus®increased fruit-set by 44% in ‘Bartlett’ pear, by 15% in ‘Van’ cherry, by 88% in ‘President’
plum, and by 6% in ‘Red Delicious’ apple. Mayer and his co-workers did not measure orchard yields.
Bee-Scent®increased honey bee visitation in Arizona watermelon for up to two days in a seedless variety and in the variety ‘Picnic,’ but it did not increase yield in either variety (Loper and Roselle, 1991).
Bee-Scent®did not improve bee visitation, yield, or monetary return with the watermelon variety ‘Royal Sweet’ nor cucumber variety
‘Calypso’ in North Carolina (Schultheis et al., 1994).
Bee-Scent®increased bee visitation in ‘Stayman’ and ‘Triple Red’
apple and increased fruit-set in ‘Stayman’ and ‘Yellow Delicious’ in Virginia (R.D. Fell, unpublished report).
Beeline®, a bee food supplement spray, may increase yield in cucumber (Margalith et al., 1984), but it does not increase bee visita- tion nor yield in carrot seed (Belletti and Zani, 1981) nor in red clover (Burgett and Fisher, 1979). Beeline® did not improve bee visitation, yield, or monetary return in ‘Royal Sweet’ watermelon in North Carolina (Schultheis et al., 1994).
The most promising and recent development with bee attractants has focused on synthetic honey bee queen mandibular pheromone (QMP). Although the existence of QMP was known since the 1960s (Callow and Johnston, 1960; Butler and Fairey, 1964), all of its compo- nents were not characterized until nearly 30 years later (Slessor et al., 1988, 1990; Kaminski et al., 1990). Researchers and industry have since synthesized and developed QMP into commercialized products.
In nature, QMP is the key pheromone that informs bees of the presence of a queen. QMP stimulates worker bees to form a ‘court’ or retinue around the queen. As bees lick and groom the queen, they pick up QMP in the process. These bees then act as messengers, spreading the pheromone from bee to bee, providing a calming, stabi- lizing effect. Among other things, the presence of a queen (i.e. her pheromones) stimulates worker bees to live longer (Delaplane and Harbo, 1987) and possibly forage more. At least one product with syn- thetic QMP (Fruit Boost®) is now marketed as a bee attractant for enhancing crop pollination. QMP works as a pollination aid by stimu- lating greater bee recruitment to treated plots and by stimulating indi- vidual foragers to stay in treated plots longer and visit more flowers (Higo et al., 1995).
QMP-based bee attractants increased honey bee visitation in pear varieties ‘Anjou’ and ‘Bartlett’ in Washington and British Columbia.
QMP-based attractant increased bee visitation in ‘Red Delicious’
apples in British Columbia, but it did not affect yield nor fruit quality
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(weight and diameter). However, the attractant increased fruit diame- ter in pear which translated to a US$427 acre21 (US$1055 ha21) increase in farmgate revenue (Currie et al., 1992b). In a later study, QMP-based attractant increased fruit size in ‘Anjou’ pear by 7%
which translated to a US$162 acre21(US$400 ha21) increase in farm- gate revenue; however, the attractant did not increase bee visits, fruit- set, nor fruit size in ‘Bing’ sweet cherry (Naumann et al., 1994b).
QMP-based attractant increased bee visitation in cranberry vari- eties ‘Crowley’ and ‘Stevens’ and in the highbush blueberry ‘Bluecrop’
(Currie et al., 1992a). Maximum attractiveness to bees was achieved in cranberry with a concentration about ten times less than that for blue- berry or for the apple and pear data cited by Currie et al.(1992b). This suggests that more attractant is needed for a three-dimensional surface (i.e. bush or tree crops) than for a flat surface (i.e. a cranberry bog).
Bee flight conditions were poor in the first year of the cranberry study and the attractant increased yield 41% and farmgate revenue by US$3564 acre21 (US$8804 ha21). In the second year, weather condi- tions for pollination were excellent and the attractant did not improve yield nor revenue. In two out of 3 years of highbush blueberry trials (Currie et al., 1992a), QMP attractant increased fruit yield by at least 6% and farmgate revenue an average of US$364 acre21(US$900 ha21).
In New Zealand, QMP-based attractant increased kiwifruit yield (trays harvested per ha) by 24%, and tended to increase export fruit weight (M. Partridge, Phero Tech Inc., unpublished data).