Puncture resistance in Sharwil avocados to oriental fruit fly (Bactrocera dorsalis) oviposition

The physiological basis for host antibiosis or nonpreference to a quarantine pest is often not understood. Studies are needed on the mechanisms that impart resistance in order to better understand how resistance might fail. Experiments were conducted to quantify the effect of Sharwil avocado skin and flesh hardness on resistance to infestation by oriental fruit fly, Bactrocera dorsalis (Diptera: Tephritidae). Three fruit collections were made at 2 wk intervals which served as replicates. Fruit were brought back to the laboratory (USDA-ARS, Hilo, HI) and either used for tests immediately or ripened at 21oC to varying degrees of hardness. Intact fruit or fruit with a small patch of skin shaved away to expose the flesh were exposed individually to 25 gravid adult females in a 31x31x31 cm screen cage for 4 h. Penetrometer readings of the skin and flesh were taken after fruit were exposed to flies using a Chatillon LTCM-100 Motorized Force Tester and conical tip (6 mm diam). Infestation rate increased with fruit age (days after harvest) and softness, and fruit with a patch of skin removed produced more flies than intact fruit, suggesting that skin puncture resistance was the main deterrent to oviposition.