Relative tolerance of four populations of Zeugodacus tau (Diptera:Tephritidae) to cold phytosanitary treatment

The pumpkin fruit fly, Zeugodacus tau, is a quarantine pest of economic importance in South and Southwest Asia comprised of at least nine morphotypes that may be described as different species in the future. Thus, it is important to test whether populations of Z. tau differ in their cold tolerance to potentially use a single cold treatment against them. We compared the relative tolerance of Z. tau third instars from wild strains of Palampur (India), Fujian (China), and Baipayl (Bangladesh) and a laboratory strain from Fuijan to cold phytosanitary treatment. Naturally infested navel oranges were placed in a cold chamber (1m³) and exposed to refrigerated air at <1.7ºC for 3, 8, 10, 13, 15,16, 18, and 20 days. Non-exposed oranges maintained at 25°C were used as controls. The numbers of dead and live larvae were recorded 24 hours after the treatment. Treatment efficacy was determined by larval mortality. Preliminary results suggest that the wild strain from Fujian was more cold tolerant than Baipayl, Fujian laboratory, and Palampur strains when exposed to <1.7ºC for up to 15 days. There were no significant differences among the four populations for doses from 16 to 20 days. Only one third instar larva from Fujian wild strain survived after 20 days at < 1.7ºC. Confirmatory tests evaluating the tolerance of several thousand third instars from Fujian wild strain are being performed to evaluate whether the cold treatment of <1.7ºC for 22 days is enough to ensure quarantine security for Z. tau.