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The fruit flies Bactrocera tau (Walker) and B. cucurbitae (Coquillett) are economically important invasive pests on numerous vegetable and fruit species in China. Due to the instability of the early spring climate, temperatures often deviate far below the normal temperature for short periods of time. Such a sudden short-term low temperature may impact the reproduction and development of the two fruit fly species. In this study, the effects of low temperatures (8, 6, 4, 2, 0, -2, and -4°С) on the development and reproduction of these two closely related fruit fly species were studied under laboratory condition. The results showed that their survival rates decreased gradually with corresponding decreases in the tested temperatures. On the other hand, their pre-oviposition periods and their adult female to male sex ratios increased, while the average number of eggs per female of each species and longevity of male adult of B. cucurbitae initially increased and later decreased after exposure to the low-temperature treatments. Overall, low temperatures promoted reproduction in B. cucurbitae and B. tau at temperatures ranging from 24°С to as low as 8°С. Development and reproduction of the two species were negatively affected when temperatures were between 8 to -4°С. The cold resistance of each developmental stage was higher in B. tau than in corresponding stages of B. cucurbitae., (© The Author(s) 2020. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Bactrocera tau (Walker) (Diptera: Tephritidae) is an economically important invasive pest, that is capable of seriously reducing the quality and yield of vegetables and fruits, it was first recorded from Fujian province in 1849 and later introduced to Yunnan province in 1912 as a result in trade fruits and vegetables of China. In recent years, with the onset of global climate change and the accompanying increase in the greenhouse effect, elevated climatic temperatures have become one of the main environmental factors affecting growth and reproduction in insects, and the optimal developmental temperature of B. tau was found to be from 25 °C to 31 °C, the growth, development and reproduction of B. tau are normal under the optimal temperature conditions. In order to determine the repercussions that elevated temperature have on B. tau, we assessed the effects that short-term (12 h) high-temperature exposures (34 °C, 36 °C, 38 °C, 40 °C, 42 °C, 44 °C, 46 °C, and 48 °C) had on the growth, development and reproduction of B. tau at different developmental stages of the fly. The results showed that the survival rate of B. tau gradually decreased in all stages following exposure to short-term high-temperatures. The pupal stage was the least sensitive to increased temperatures. The pupae withstood the highest lethal temperature, having an LT 50 of 42.060 °C, followed by female adults (40.447 °C), male adults (40.013 °C), and larvae (36.740 °C). The egg stage, which was the most susceptible to heat increases, had the lowest LT 50 (38.310 °C). No significant effects were observed in the developmental stages of B. tau at temperatures from 24 °C to 38 °C. The development duration was significantly prolonged at 40 °C (P < 0.05) in the eggs (2.830d), larvae (7.330d), and pupae (8.170d) (P < 0.05). B. tau was unable to survive at temperatures above 42 °C. The pre-oviposition of female adults was extended, the average egg number per female showed a downward trend, the longevity of adults gradually shortened, and the ratio of female to male offspring increased as temperature increments were increased. In summary, short-term high-temperatures over 42 °C were not suitable for successful development of B. tau, while short-term high-temperatures over 40 °C were not suitable for successful reproduction in B. tau.