132 Semi-commercial-scale Ultra-low Oxygen Storage for Disinfestation of Mexican Fruit Fly in Grapefruit

Abstract

A treatment schedule for disinfesting grapefruit of Mexican fruit fly with refrigerated (14 °C) storage for 21 days in ultra-low oxygen (0.05 kPa) was tested using a fully loaded, 24-ft sea freight container. The objective of this research was 3-fold: 1) evaluate the ability of a free standing Electronic Oxygen Control system to maintain 500 ppm of oxygen for 21 days inside the sealed container, 2) evaluate the mortality of third instar Mexican fruit fly larvae stored for 21 days inside the sealed container, and 3) evaluate fruit market quality after 21 days inside the container. The container was loaded with 17 pallets of red-fleshed, `Rio Star' grapefruit. Three boxes from each pallet were evaluated for fruit quality (decay (%), visible disorders (%)) after 21 days of treatment and again after 14 additional days of storage in air at 10 °C. Four cartons, each containing 24 fruit infested with third instar, Mexican fruit fly larvae, were each placed on top of a pallet in four different container locations. Upon completion of treatment, larvae were evaluated for survival. In the first replication, no fruit fly larvae survived the low oxygen treatment. In the second replication, oxygen concentration was less controlled, and 60 pupae survived the treatment. Treated and control grapefruit had similar incidence of decay when the treatment was terminated, however no sporulation was observed in fruit stored under ultra-low oxygen. Grapefruit exposed to ultra-low oxygen had a higher incidence of visible disorders, consisting of darkened, sunken areas on the fruit surface. It is unclear whether this damage is attributed to fluctuating levels of oxygen, deleterious volatiles produced during treatment, or a sensitivity of the fruit to low oxygen.