Studies on the apple pollination by Osmia : (II) Characteristics and underlaying problems in utilizing Osmia

In this paper are given the account on the problems in utilizing Osmia as pollinators of the apple and some suggestions for the further development were made. 1. Flower-visiting habits : Osmia predominantly and constantly visits the apple flowers if the other competing flowers in blooming are few around the apple orchards. 2. Natural enemies : The natural enemies of O. cornifrons (Radoszkowski) are as follows and their percentage parasitism on it in Nagano and Aomori Prefectures are shown in Tables 1-2 respectively. 1. Monodontomerus osmiae Kamijo, 2. Leucospis japonica Walker, 3. Attagenus japonica Reitter, 4. Ptinus japonicus Reitter, 5. Mite, 6. Fungus, 7. Others (Unknown species and diseases). In Aomori Pref. the species numbered 1, 2, 3 and 4 above were not found under the authors' present investigation. Only certain natural enemies such as the mite, the fungus and the others can be controlled by adding the new trap nests (reed tubes) in replacing the old ones. 3. Emergence period of Osmia and flower-blooming period of apples : The apples begin to bloom toward the end of April and the period lasts about 20 days in Nagano and Aomori Prefectures. On the other hand, O. cornifrons usually begins to fly two weeks before the blooming of the apples. Therefore, flower of other plants are required to well establish Osmia in the apple orchards. 4. Pollinizer : The effect of the pollination by Osmia is more successful in the orchards in which many varieties of the apples are found. It is easily assumed from the fact that the apples are the cross-pollinating plants which demand the different varieties' pollens. 5. Spray program : The applications of the insecticides such as the organic phosphates (in Nagano Pref.) and the Denapon (in Aomori Pref.) two weeks after the bud breaking and the petal fall of the apples have been proved to be harmful to Osmia when they are applied near by the nesting sites of Osmia and it reduces the bee p opulations. So it is necessary to protect Osmia from the application of these insecticides.