瓜實蠅之生態研究

Abstract

瓜實蠅各蟲期，在臺灣南部，週年可見到，但其成蟲的出現盛期則為6至8月間。其寄主植物，經在臺灣南部調查結果，乃以葫蘆科種類為主，茄科中之番茄，在果實成熟時偶有發現被其寄生，但茄子類卻從未發現被其為害。在葫蘆科諸寄主中，以甜瓜類之黃香瓜、綠香瓜、苦瓜及越瓜等被害最烈，胡瓜、絲瓜等次之，其餘瓜煩雖育被害，但不甚嚴重。其成蟲之棲息處所，以番石榴、柑桔、柚子、檸檬、芒果等果樹園為最多。其在一日中之活動盛期，乃受上午9點時溫度之高低所左右。其活動之適宜溫度為19至29℃。 The melon fly. Dacus cucurbitae Coquillett, has long been a serious pest of cucurbitacious crops in Taiwan. The losses of production caused by melon fly were estimated over 30% This study is chiefly concerning with the preference and abundance of melon-fly, and the habitats where flies mostly tend to congregate. Degree of preference of the fly for its host was evaluated by growing several-species of cucurbitaceae and solanaceae in field all year round. Different stages of fruits which formed after 5, 10 and 15 days were taken from field to laboratory and placed over sand in holding boxes to recover pupae developing from immature larvae in the host material. The sand was screened weekly and pupae were then counted. Habitats of the melon fly were investigated in Tainan, Kaohsiung and Pintung areas. Male attractant, anisylacetone 98% added DDVP technical grade 2%, was used to attract male fly in. the plastic traps which were hung under the trees of orange, pomelo, lemon, guava, mango, carambola and bullock’s heart. The traps were emptied and attractant renewed twice a month. Activity period of melon fly also was investigated by using the same procedure of trapping the male fly in cucumber field. Flies were counted on daily at 9: 00, 12: 00, 15: 00 and 17: 30. Temperatues of atmosphere, showing on the thermometer hung in the cucumber field, were recorded at the same time. From the information gathered in both field and laboratory, flies of any life stage could be found year round in southern Taiwan (Table 1). Their surge of abundance concentrated in the period of June to August. This might correlate with the fruiting peak of water melon and muskmelon which were popularly and abundantly grown in river-beds and areas where these melons were planted with the first crop of rice. During August and September, there were the typhoons as well as heavy rainfall, population of melon fly was suppressed sharply to its lowest level. After October, the raining season was over, water melon and cucumber were again grown in both the river beds and the rice field after second crop, population of melon fly raised again to its second peak. Melon fly was sparse in the months of March to May when the spring grown water melon was still at the young stage. Other varieties of cucurbit were scarcely grown because the first crop of rice was in the growing season (Fig. 1). Preference of melon fly was evaluated by counting the number of pupae per 100 grammes weight of cucurbit. The results, as shown in Table 2 revealed that the flies preferred bitter cucumber, muskmelon and oriental pickling melon best, cucumber and vegetable sponge the next, water melon, squash and calabash gourd the least. Infestation of flies varied in ages of fruits in different varieties of cucurbit. The characteristics of eggs deposition, of melon fly, might be affected by the structure of the skin of cucurbitacious fruits. The skin of bitter cucumber, for example, was very smooth and tender into which flies preferred to lay their eggs any time before the fruits were harvested. For water melon, squash and vegetable sponge, the skin of which were very tender in the early stage of young fruit, into which flies preferred to lay their eggs too. But flies could rarely cause much damage to the full grown fruits as the skin of which getting harder. Flies did not lay as many eggs into the young fruits of calabash gourd as they did into the other fruits of cucurbit though the skin of young calabash gourd fruits were tender too. It might be due mainly to the fuzzy skin of the young fruits of calabash gourd which hindered the flies laying eggs. Flies did not damage in green stage of tomato fruits, but few pupae of melon fly had been obtained from the fruits as the skin of which became pink in color about 1/3 or more of the fruit surface. Male melon flies were trapped mostly in fruit trees such as guava, orange, lemon, pomelo and mango year round in Tainan, Kaohsiung and Pintung areas. More flies were trapped in the mixed planting of guava, pomelo, mango and longan. On these fruit trees, many insects such as mealy bugs and aphids always produced a great deal of honey dew which the flies preferred. It was clearly shown that the flies did not remain in the field of cucurbit beyond deposition of eggs. Fluctuation of flies varied from place to place. It might be affected by local environment, such as the different growing seasons of cucurbit and the uncertain local showers that occurred during July to September. Pruning the tree also caused the flies to move out of the field, as shown in Table 3 in Kaohsiung area, when the leaves of guava were pruned in January, there was not any fly caught thereafter. But the flies increased gradually as the new leaves of guava grew. Timing activity of melon fly was observed daily at different hours of the day from December 1971 to August 1972. Large numbers of melon flies were caught in traps before noon in sunny days, as shown in Table 4. An extraordinary number of flies usually caught on the bright and warmer days after several days of low temperature and light rain during the spring season. Activity of melon fly also evidently influenced by temperature. The lowest and the highest temperature that the melon flies appeared ranged from 16 to 34℃, but the favorable temperature range seemed to be from 19 to 29℃. There was evidence indicating that the peak activity of melon fly during a day was mainly affected by the temperature showing at 9:00. Several indications which revealed from the data would be worth to be summarized as in the following: (1) If the temperature was below 20℃ at 9:00, the number of melon flies trapped during 9:00~12:00 would be the highest, 12:00~15:00 the second, dawn to 9:00 the third, after 15:00 the least. (2) If the temperature was between 21~25℃ at 9:00, the number of melon flies trapped during 9:00~12:00 would be still the highest, but the second would be changed during dawn to 9:00, and. the least after 12:00. (3) If the temperature was above 25℃ at 9:00, the number of melon, flies trapped would be orderly during dawn. to 9:00 the highest, 9:00~2:00 the second, 12:00~5:00 the third, but there would be not any fly appeared after 15: 00.