Possible distribution and establishment of two species of tropical fruit flies, melon fly and oriental fruit fly, in japan and its adjacent temperate countries

Abstract

1. Total sums of effective temperatures for the completion of whole life cycle (from the beginning of egg period to the first oviposition of the adult) are 650 degree-days for Dacus cucurbitae and 610 for D. dorsalis. Both values are constant in the temperature range between 15°and 30°. Judging from these values the number of generations during the temperate season of a year may be expected to be one or two in Korea, North-China and in the northern half of the mainland of Japan, and two or three in its southern half. 2. Eggs, maggots and pupae all die of cold within 40~55 days at the constant temperatures below 8°, within 40~50 days at varying temperatures below 11°, and within 50~60 days at temperatures falling gradually to 8°. The latter two temperatures are those actually found in the cold season of the year of the temperate climates. 3. Adult flies can live about 100 days at the constant temperatures between 9° and 25°, but cannot survive much longer than 30 days at temperatures below 8°. Under the alternating low temperautres consisting of average daytime and night temperatures of winter in Japan the flies can maintain their natural longevity, if the mean degree is higher than 9° at which the flies display feeding activity. When night temperatures are lower than 8°, especially lower than 0°, their durations of life are exceedingly shorter than those found at the constant temperatures of the same degrees regardless of the daytime temperatures. If the flies are exposed to the winter temperatures of west-southern Japan through passing a series of temperatures falling gradually from autumn to winter starting from the autumn temperatures of Formosa they will not live much longer than 100~160 days in D. c. or 80~125 days in D. d., when the exposures begin from September to November and 40~50 days in the case started from December. Through such gradual exposures the cold-hardiness could be enlarged about 1.5 times in comparison with that found in the sudden one, whereas in all the cases the flies died until the end of February. Critical temperatures for copulation and oviposition could not be changed by such gradual exposures. © 1964, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.