Poor Host Status of Australian Finger Lime, Citrus australasica, to Ceratitis capitata, Zeugodacus cucurbitae, and Bactrocera dorsalis (Diptera: Tephritidae) in Hawai'i

Simple Summary Tephritid fruit flies are major economic pests for fruit production and impede international trade. Different host fruits are known to vary in their suitability for fruit flies to complete their life cycle. International regulatory standards that define the legal host status for tephritid fruit flies categorize fruits as a natural host, a conditional host, or a nonhost. For those fruits that are natural or conditional hosts, infestation rate can vary as a spectrum ranging from highly attractive fruits supporting large numbers of fruit flies to very poor hosts supporting low numbers. Finger lime, Citrus australasica, is a new crop in Hawai'i, and no information existed on its susceptibility to Hawai'i's tephritid fruit fly pests. Host status testing was conducted using no-choice cage tests and field collections. Ceratitis capitata and Zeugodacus cucurbitae readily oviposited into finger limes, but individuals rarely developed to the pupal or adult stage. Finger lime was not infested by Bactrocera dorsalis and is probably a nonhost. For export, a postharvest treatment may still be required despite the very low infestation rate. Heat treatment, irradiation, and a systems approach are options to reduce the risk of exporting tephritid fruit flies in Hawai'i finger limes. We examined the host status of the Australian finger lime, Citrus australiasica F. Muell. (Rutaceae), to Hawai'i's tephritid fruit fly pests using laboratory and field studies. In high-density (500 flies, 1:1 males and females) no-choice cage exposures (25 x 25 x 25-cm cage size), both undamaged and punctured finger limes were infested by Ceratitis capitata and Zeugodacus cucurbitae at a low rate compared to papaya controls, whereas Bactrocera dorsalis did not infest undamaged fruit, suggesting finger lime is a nonhost. In low-density (50 females) no-choice cage exposures, C. capitata and Z. cucurbitae readily oviposited in undamaged fruit but individuals rarely developed to the pupal or adult stage. For C. capitata, 274 finger limes exposed to 2000 gravid females, which laid an estimated 14,384 eggs, produced two pupae and no adults. For Z. cucurbitae, 299 fruit exposed to 2000 gravid females, which laid an estimated 4484 eggs, produced four pupae and one adult. Field sampling of undamaged fruit from the tree and off the ground from commercial farms produced five C. capitata pupa and one adult from 1119 fruit, for an infestation rate of 0.05 flies per kilogram of fruit; field collections found no natural Z. cucurbitae or B. dorsalis infestation, but the number of fruit available was too low to demonstrate nonhost status with a high degree of confidence.