Lethality of Cold to Third Instars, Pupae, and Pharate Adults of the Mexican Fruit Fly (Diptera: Tephritidae)

Abstract

Tolerance of Mexican fruit fly, Anastrepha ludens (Loew), 3rd instars and puparial stages to 1.1°C was evaluated. Mexican fruit flies were more susceptible to cold during the first few days after cessation of larval feeding (through the cryptocephalic pupal stage) than feeding 3rd instars. That is a period of intense morphological change for the insect. First-day phanerocephalic pupae, however, were estimated to require twice as much time to achieve LT99.9968 at 1.1°C compared with feeding 3rd instars. Although the Mexican fruit fly does not diapause, the phanerocephalic stage is the diapausing stage for tephritids that do diapause. A major implication of this study is that cold-treated fruits are usually packed before treatment, and larvae could conceivably emerge and pupate within the packaging before temperatures are reduced to sufficient levels to stop development. Newly formed phanerocephalic pupae and pharate adults >3 d old are more tolerant of cold than 3rd instars. Therefore, fruits should not be held at temperatures after packaging that allow sufficient time for fruit fly development to the phanerocephalic pupa.