Effects of high-temperature stress and heat shock on two root maggots, Bradysia odoriphaga and Bradysia difformis (Diptera: Sciaridae)

Bradysia odoriphaga and B. difformis (Diptera: Sciaridae) are devastating pests of vegetables, ornamentals and edible mushrooms. In Chinese chive fields, the two Bradysia species occur with similar regularities: outbreaks in spring and autumn, and population decreases in summer. Temperature may be an important factor restricting their population abundance in summer. Here, we performed a life-table study under constant high temperatures and assessed the tolerance of two Bradysia species to heat shock. Life parameters of the Bradysia species indicated slow developmental rates, and low survival rates and fecundity, when the temperature was higher than 30 °C. At 34 °C, individuals were unable to reach the adult stages from eggs. Moreover, temperatures above 36 °C showed lethal effects, decreasing their survival rates. The median lethal time (LT50) values of 4th instar B. odoriphaga and B. difformis larvae were 46.82 and 32.97 h, respectively, while the values at 38 °C were 2.12 and 1.51 h, respectively. The 4th instar larvae and pupae possessed higher thermotolerance levels than adults and eggs, indicating sensitivities to heat stress. Moreover, B. odoriphaga was more thermotolerant than B. difformis. Thus, weak thermotolerance levels may restrict their occurrences during the period of summer heat, and the difference in thermotolerance levels between the two species may be related to their regional distributions.