Commodity Heating Medium and Mexican Fruit Fly Mortality

Abstract

The objective of this research was to investigate whether the medium used to transfer heat to a commodity influenced the mortality of Mexican fruit fly larvae. A similar 2-h heat dose was delivered to grapefruit via immersion in a variable temperature water bath or via exposure to a rapidly circulating gas. The concentration of oxygen and carbon dioxide inside the grapefruit was analyzed at 30-min intervals and grapefruit center temperatures recorded every 60 s during heating. The mortality of larvae located inside grapefruit during heating in a controlled atmosphere or in hot water was significantly higher than that of larvae located inside grapefruit heated in air. The internal atmosphere of grapefruit heated in a controlled atmosphere or in hot water contained significantly higher levels of carbon dioxide and lower levels of oxygen than grapefruit heated in air. Larval mortality was compared after larvae were heated in media by rapidly circulating air or by an atmosphere containing 4 kPa of oxygen and 18 kPa of carbon dioxide to evaluate whether the altered atmosphere or a heat-induced fruit metabolite was responsible for enhanced mortality. The significantly higher mortality of larvae heated in media in the presence of an altered atmosphere suggested that the altered atmosphere enhanced larval mortality. Results from this research suggest that reducing oxygen and or increasing the level of carbon dioxide during heating can enhance mortality of the Mexican fruit fly and potentially reduce the heat dose required for quarantine security.