INTRODUCTION:

Generally, two kinds of flowers are present on vine crops (cucumber, squash, pumpkin, watermelon, cantaloupe and other melons). These are males and females which are located at different places on the plant. This condition is called monoecious. Male flowers (staminate) usually appear first, followed by female flowers (pistillate). Some flowers will have both sexes on occasion; these are called hermaphrodites. Female (fruit-producing) flowers on vine crops are usually only open for one day and then only from 10:00 a.m. to 2:00 p.m.

Because they are monoecious, the pollen from the male must be transferred to the stigma of the female. This is called pollination. Fertilization then takes place and seeds and fruit are produced.

Cucumbers and watermelons generally have both male and female fruit-producing flowers. Most cantaloupes, and so-called "mixed" melons (honey dew, Casaba, Persian) have male (staminate) flowers and bisexual or perfect (hermaphroditic) fruit-producing flowers.

Insect pollination is necessary for commercial production of most vine crops. The honey bee traditionally has been the preferred pollinating agent. This is not to say that other pollen transferring insects (butterflies, solitary bees) are ineffective. One kind of the latter group in particular, Peponapis sp., is extremely adept at pollinating particular vine crops (squash, pumpkin and gourd). However, two major elements distinguish honey bees from other potential pollinators: (1) they develop populations capable of generating a large pollinating potential, and (2) a technology is in place to rear, manage and move these large populations as the need arises.

Although benefitting from honey bee pollination, most vine crops are poor sources of pollen and nectar. This means that honey bees cannot be expected to make any significant population gains while located on these plants. Indeed, the opposite is often the case. Bees populations can go "downhill" and may become depleted of food stores in commercial vine crop plantings.

CROP SPECIFICS:

The best review of pollination requirements of specific crops continues to be Agricultural Handbook 496, Insect Pollination of Cultivated Crop Plants, by S.E. McGregor, published by the Agricultural Research Service, USDA, July, 1976. This valuable resource, which many call the "pollinator's bible," is out of print, but still available from both the Tucson Bee Laboratory, 2000 E. Allen Rd., Tucson, AZ 85719 and the Weslaco Bee Laboratory, 2413 E. Hwy. 13, Weslaco, TX 78596. The following are brief summaries of the volume's information on specific crops, as well as added comments based on newer information:

1. Watermelon: At least 1,000 grains of pollen must be evenly deposited on the three lobes of the stigma to produce a uniform fruit. This equals to about eight bee visits per flower. Uniformity is all important; an imbalance in pollination inevitably results in a misshapen fruit. Honey bee visits are primarily in the morning, from 1 to 2 hours after sunrise. The number of visits by bees should be maximized; the more the better. It has been suggested that one bee per hundred flowers is an adequate pollination level. Seedless, triploid watermelons also require pollination. There is no uniform recommendation for pollinating units per acre; a calculated literature average is about 1.3 hives per acre.

2. Cucumber: The pollination requirements vary greatly depending on variety and geographic area. Several hand harvests can occur during the growing season. Machine harvest has increased the need for bees by demanding more rapid, uniform fruit set of mostly female (gynoecious) flowers. The stigma is most receptive in early morning and several hundred pollen grains should reach the stigma for effective fruit set. Again, at least 8 honey bee visits are necessary; the more the better. There is no uniform recommendation for pollinating units per acre; a calculated literature average is about 2.1 hives per acre.

3. Squash and Pumpkin: Male flowers outnumber female flowers. The plants are mostly receptive in the morning, primarily before 9 a.m. Seed number and fruit weight increase in proportion to the amount of pollen transferred. There is no uniform recommendation for pollinating units per acre; a calculated literature average is about 1 hive per acre.

Solitary bees (Peponapis sp.) are principle pollinators of squash and pumpkin. Population levels are variable, but when these occur in large numbers, supplemental pollination by honey bees can be reduced. Growers should make every effort to conserve these bees by establishing sanctuaries to conserve nesting sites and food sources.

4. Cantaloupes and other "mixed" melons: Caged honey bee studies indicate hermaphroditic flowers are not capable of self-pollination. Fruits with less than 400 seeds are usually considered culls; there is strong correlation between number of seeds and fruit size/weight. Flowers are receptive throughout the day. Many flowers must receive more visits than necessary to ensure effective fruit set. One bee per 10 hermaphroditic flowers is a general rule of thumb. There is no uniform recommendation for pollinating units per acre; a calculated literature average is about 2.4 hives per acre.

Notice the recurring sentence for each of these crops: "There is no uniform recommendation for pollinating units per acre." This is the bind both beekeeper and grower find themselves in when determining the scope of any pollination contract. When the facts are not fully known, the parties to the contract then must use what amount to best guesses.

Of special significance is that both beekeeper and grower be intimately familiar with reproduction requirements for each crop. It is not enough to know just the broad outline. For example, seedless watermelons would at first glance appear to not require pollen transfer because seeds are not the goal, nevertheless, the plants benefit from pollination. Some fruit is self compatible, but won't set without intervention of an insect pollinator. Many plants require cross pollination, the transfer of pollen not only among plants, but among varieties.

NEW VARIETY DEVELOPMENT:

Plant breeders continue to produce new varieties of crops for agriculture. A quick look at recommendations such as amount of fertilizer needed, pH of the soil, irrigation, etc., however, may reveal that each new variety will have different requirements than the old. This concept also applies to pollination. Many now agree that pollination should be one of the major inputs that growers must concern themselves with along with water, fertilizers and insecticides. Unfortunately, although quantity and quality of yield and possible resistance to diseases/insects are often exhaustively studied in new varieties, pollination requirements usually get less attention.

The fact that pollination concerns are not always addressed is logical. They are the most expensive and difficult issues to study. The physical number of experiments needed to ensure reliability is part of the problem. The fact that studies must be carried out in small-scale plots and in isolation from other plants, usually in cages, which does not mirror the reality of production fields also affects the results. Finally, the last thing the plant breeder needs is to add another organism, the honey bee, which incorporates another large set of variables, into the pollination equation. Unfortunately, all this must be done if any useful information is to come from these kinds of investigations.

The release of new varieties, therefore, must be tempered by the knowledge that several more years of study and testing by growers on a large-scale in the field are needed before any crop can be considered successful. A classic example of this is recent, large increase in rabbiteye blueberry cultivation in the southeastern U.S. correlated with release of new varieties. Yield has not measured up to everyone's expectations. One reason appears to be lack of pollination.

Native pollinators do a much better pollination job on rabbiteye blueberries than honey bees, but large acreage tends to limit the pollinating efforts of relatively small populations of these efficient bees. Although there is little doubt that honey bees are reluctant and inefficient pollinators of these blueberry varieties, the idea of oversaturating fields (4 hives to the acre has been recommended), forcing these insects to forage on the blooms, has yet to be tested.

Varietal difference must also be taken into account when evaluating previous research results like those found in Agriculture Handbook 496. There is danger in assuming that published research results are automatically valid in newer varieties of the same crop. In addition, planting identical varieties in different geographic locations can also effect yields in a number of ways.

IMPORTANT FACTORS IN POLLINATION:

The first question usually asked about pollination is how many hives to the acre for a specific crop? A rule of thumb is to begin with one colony per acre and to adjust from there based on a large number of variables. Because all honey bee colonies are not equal, it is often better to find another determination of pollination potential. This might include counting the number of bees in the field or perhaps determining the number of individual foragers in relation to the number of flowers that need pollination.

Other considerations are the number of wild pollinators available, the characteristics of each honey bee colony and their position in the field. Relative attractiveness of the crop and its blooming characteristics also determine scheduling of colony movement.

Competition Among Blooms:

Vine crops are often not as attractive to honey bees as other plants. Practical experience shows this is particularly true for cucumbers. Given the choice, honey bees often prefer other crops like avocadoes and the various minor and major honey plants the state of Florida has to offer. Thus, it becomes extremely important to determine whether competing blooming plants are present when cucumbers are to be pollinated. If bees are diverted to competing crops, the only solution is to bring in more bees that are not yet accustomed to the plant mix of an area and hope they get on with the job at hand. The maximum range of honey bees is usually considered to be a two-mile radius from the colony, however, usually the insects forage at lesser distances from their hive.

Colony Strength:

Colony strength, the physical number of bees in a hive, can make a big difference in pollinating potential. The more individuals in the colony, the more available for pollination work. It's that simple. Estimating colony strength, however, is not often easy, especially for the inexperienced. The rule of thumb is that a minimum of five standard (Langstroth) frames of brood with more than enough bees to cover six to eight frames is needed.

A more precise measurement of pollinating potential would be in square inches of brood/bees. Oregon grade A standard, for example, calls two brood boxes with 3,000 square inches of comb, 1,000 square inches to be occupied by live brood. This measurement eliminates problems with different size combs. Unfortunately, this standard is not comparable to Florida conditions; two brood boxes are rare. Generally, if a hive is opened and bees appear to boil out, strength is considered sufficient. Finally, a vigorous queen is needed, along with plenty of stored pollen and honey.

Colony Placement:

The closer to a hive of bees, the more chance plants will be pollinated. For best results, honey bee colonies should be distributed throughout fields. This is particularly true in blocks larger than 40 acres. Colonies along the edges of fields will more effectively pollinate than those located farther away. In addition, there is evidence that honey bees preferrably forage up and down rows and not across them.

Scheduling:

Bees should be moved to the crop just as it begins to flower for the best pollination results. This is particularly important in high value crops like watermelons, which are more valuable early in the season. There is a tradeoff, however, because bees orient to their location as time goes on, and will inevitably forage over wider distances. Thus, the earlier they are brought in, the sooner their foraging activities might take them outside the confines of the field.

Attractants: