西条ガキにおける花粉媒介昆虫の利用に関する研究 : シマハナアブの授粉効果

To ascertain the ability of Eristalis cerealis Fabricious as an insect pollinator of kaki(Japanese persimmon, Diospipyros kaki L.) "Saijo" which genetically lacks male flower and needs cross pollination for fertilization, 4 treatments listed below were applied to selected arms of 9-year-old trees of "Saijo" using 4 replicate single-tree blocks.
1. Non pollination -- Arms were placed in plastic screen cages (2.3m×2.5m×1.0m) for preventing insects from visiting the flowers during bloom.
2. Eristalis cerealis pollination -- Arms were placed in plastic screen cages, in which 5 of reared Eristalis cerealis were confined during bloom. Before the confinement, these insects were left for 2 days in cages installed over arms of blooming pollinizer trees("Zenjimaru") interplanted in the "Saijo orchard".
3. Open pollination -- Arms without cage were free for insects to visit the flowers.
4. Hand pollinatlon -- All flowers on arms without cage were hand-pollinated with "ZenJimaru" pollens.
The hand pollination resulted in the largest number of seeds per fruit, followed by the open pollination. Very few seeds were found in the fruits of the Eristalis cerealis pollination and no seeds in those of the non pollination. Decrease in seed number per fruit due to these treatments promoted the physiological fruit drop occurring for several weeks after blooming and lowered the fruit weight at the harvest time. The only good effect of the decrease in seed number was that it tended to raise the level of soluble solids in juice of harvested fruits. Thus,it is clear that Eristalis cerealis did not work effectively as a pollinator of "Saijo" in this experimental conditions.
On the other hand, our observation exhibited that 31 species of insects were in action in the "Saijo" orchard during the blooming time, some of which including Eristalis cerealis were visiting the flowers of "Saijo" trees.