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The purpose of the present paper is to prove the occurrence of the arrhenotokous parthenogenesis in Osmia excavata All ken and Osmia cornifrons (Radoszkowski) by means of the biological experiments. The principles of experiments arc (1) to liberate the virgin females which are controlled under low temperature conditions to the field later than their normal flying season, or (2) to liberate the virgin females of the newly introduced species to a habitat where the species does not occur. The first method was devised for Osmia excavata and the second to Osmia cornifrons. It is clear that Osmia cornifrons has never been found in Kyushu. Accordingly, the liberation of the virgin females of this species in Kyushu may afford a valid key to prove the occurrence of parthenogenesis. A preliminary experiment by the first method for Osmia excavata was succeeded in 1954 (see Table 1), but the following summary is the result of experiments conducted in 1955. On February 8, 1955, the overwintering adult females of Osmia excavata were put into the thermostat regulated at 4~5℃. They were 60 in number, devided 3 groups containing 20 bees each. The first group of the red marked bees was liberated on May 9, at 10: 00 (fine, 20℃), transfering immediately from the thermostat (5℃) to the field. Then, 7 out of 20 flew away soon, and 13 bees early next morning. After all, 14 females were established until May13 afternoon. The results of their nesting activities were shown in Table 2. The second liberation of the white marked bees was practised a w eek later, on May 16, at 16:00 (fine, 26℃). In this case, 17 out of 20 flew away early next morning, 1 at noon, and the rest on May 18 morning. Among these, only 5 bees were established. The results were shown in Table 3. The third liberation of the yellow marked bees was conducted a fortnight later from the first one, on May 23, at noon(fine, 25℃), transfering immediately from the thermostat (5~7℃), too. In this case, 10 out of 20 flew away on that day, and the rest next morning. Although 8 out of 20 established, none of them completed a nest or a larval cell with only one exception. For example, one bee began nesting on May 25 morning, but her first egg was deposited on May 31 evening. Thus, it took about a week to construct a single larval cell! It seemed probable that these unhappy results were caused principally by the lack of pollen and nectar at that time. The second method for Osmia cornifrons was conducted as follows: A short series of nests of Osmia cornifrons was collected at Ka r u izawa, Honshu, in the summer of 1954. From these, 23 females were obtained. On February 8, these (overwintering) females were put into the thermostat regulated at 4~5℃. The liberation was conducted on April 5. In this case, 19 out of 23 flew away within a week and 4 found to be dead. Among these, only 4 were established. The results were shown in Table 4. It is concluded through Tables 2 to 4 that th e males of Osmia excavata and Osmia cornifrons are produced from the unfertilized eggs. It is of great interest to note that the following facts were clarified by the liberations of virgin females of Osmia excavata during the off season. 1. The structure of the nests were confused. Namely, (a) the lengths of larval cells were proved to be irregular, making a remarkable contrast to the normal nest, in which the larval cells became shorter towards the entrance, and (b) an empty cell was built between the larval cells. 2. Owing to the shortage of the suitable pollen and nectar, (a) the nesting abilities of female bees were decreased and (b) most of bees were forced to divide their labours. For example, the female bees of Osmia excavata are used to collect pollen and nectar simultaneously from the flowers of Brassica. While, in the off season of flowering period of Brassica, it was frequently observed that she sucked honey from the nectar of the flowers of white clover, and then flew away for searching pollen. Several kinds of pollens (undetermined) were detected in these cells. 3. The parasitism of the larvae of a species of Meloid beetles was newly observed. 4. Many larvae were killed by the decease caused by an unknown bacterium. 5. Many unhatched eggs were recorded beyond expectation.
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