Cucurbit Genetics Cooperative Report 20:45 (article 19) 1997
Bill Rhodes, Katherine B. Gruene and W. Michael Hood
Horticulture Department, Clemson University, Clemson SC 29634
Adlerz (1) reported that 8 honey bee visits are necessary to effect fruit set on diploid watermelon. Although a large number of male flowers exist on diploid pollenizer rows in a triploid field, the preferred ratio of diploids: triploids seems to be 1:10. If a ratio of 1:2 or higher could be pollinated effectively, the grower would realize a greater return.
In 1996, we evaluated pollination on triploid plants in an effort to measure how many honey bee visits are necessary to produce fruit set on triploid plants.
Materials and Methods. Alternating row segments of four diploid and three triploid plots, each with 7 plants, were transplanted at the Clemson University Musser Farm. The female flowers of the triploid plants were covered in the evening and uncovered the next morning to count and time bee visits to the female flowers. Adjacent to this small plot was a planting of three diploid, five tetraploid and 15 triploid hybrids from these parents for evaluation. A hive of honey bees was transferred to the middle of an outside row after plants began to bloom.
Four-channel stopwatches were used to measure the duration of bee visits, and paper covers were used to close female flowers the evening before opening. The number of bee visits were controlled by uncovering the flower and allowing 0-16 visits before closing. We measured visits and times for only honey bees on most flowers and visits and times for a small wild bee.
We observed that bees spent a large amount of time on the male flowers of the triploids. These male flowers are normal in appearance even though they are virtually devoid of pollen. Nevertheless, the bees were not only attracted to the functionless males but spent time there. We decided to measure just how much time was being spent on the triploid males as well the triploid females. We also decided to expand our study of male and female flowers to 22 more triploid plants in adjacent plots. By taking 10 min samples of bee activity on each triploid plant, we were able to sample variability among varieties and across the field. We also counted the number of open male and female blooms on each plant each day of observation to estimate total plant activity.
Results and Discussion. It was difficult to to obtain more than 10 honey bee visits in a single morning from 7-11 a.m. because of personnel schedules and the lack of bee activity during the pollination of the small 7 x 7 plot. Consequently, the number of bee visits necessary for fruit set was determined on only a single fruit. The only controlled triploid fruit set was obtained from 10 honey bee visits, but large numbers of abortions at equal or higher numbers of visits suggests that this single figure is low.
A very small wild bee was a very frequent visitor to the female flowers, but large numbers of carefully monitored visits did not result in fruit set. A few bumblebees were pollinators, but their effectiveness was not measured.
Bees made more visits and spent more time on triploid males than on triploid females. Bees spent 161 sec per triploid plant on the male flowers and only 23 sec per triploid plant on the female flowers. On this basis we speculate that an increase in triploid plants in a production field simply increases the amount of time wasted by the Apis bees. This wasted time does not appear to be beneficial to either the bees or to triploid production. Our observations suggest that a gynoecious triploid hybrid may prove more productive.
Literature Cited
- Adlerz, W.C. 1966. Honey bee visit numbers and watermelon pollination. J. Econ. Entomol. 59(1):28-30.