Phytosanitary cold treatment for oranges infested with Bactrocera zonata (Diptera: Tephritidae)

Cold Disinfestation for 'Red Globe' Grape (Rhamnales: Vitaceae) Infested With Drosophila suzukii (Diptera: Drosophilidae)

The spotted wing drosophila, Drosophila suzukii Matsumura, which is widely spread in the main soft-skinned fruits production areas in China, presents a threat to importing countries. In order to develop a phytosanitary cold treatment measure for preventing the movement of this drosophila fly, cold tolerance of six immature life stages of D. suzukii was compared followed by time-mortality and large-scale confirmatory tests on the most tolerant stage in grape fruit. Egg was defined as the most cold-tolerant stage by comparing the mortality of all the immature stages (egg, first, second, and third instars, early and late pupa) treated at 0 and 2°C. The minimal lethal time (LT) for 99.9968% mortality (95% confidence level [CL]) estimated by the probit model was 10.47 d at 0°C and 11.92 d at 2°C, respectively. Hence, 11 d (at 0°C) and 12 d (at 2°C) were chosen as the target time to conduct the confirmatory tests. No survivors were found among the estimated 50,385 and 57,366 treated eggs, which resulted in the efficacy of 99.9941 and 99.9948% mortality (95% CL) at 0 and 2°C, respectively. Our study suggests a technical basis for cold disinfestation on D. suzukii in cage-infested Chinese 'Red Globe' (Vitis vinifera L.) grape, which could provide flexible phytosanitary treatment for control of D. suzukii in the international trade of grape.

The Effects of a Cold Disinfestation on Bactrocera dorsalis Survival and Navel Orange Quality

Citrus sinensis (L.) Osbeck is an important economic product in South China, but the presence of quarantine pests in this product proposes the potential threat to international trade security. To find a proper phytosanitary cold treatment for Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), commonly called oriental fruit fly, one of the most serious quarantine insects in navel orange, eggs in petri dish and larvae in navel orange fruits were exposed to a 1.7 °C cold chamber for 0–11 days to compare the tolerance to cold treatment. The 2nd instar larva (4 days) is the most tolerant stage, and the estimated time for 99.9968% mortality at the 95% confidence level is 11.3 (9.5, 14.6) days. Then 15 days was selected as the target time for the confirmatory tests, resulting in no survivors from 37,792 treated larvae with the efficacy of 99.9921% mortality at the 95% confidence level. The quality assessments were conducted to compare the effect on the navel orange fruit between cold treatment and the conventional cold storage. Results indicated that the cold treatment did not negatively affect the fruit quality. Therefore, this cold treatment showed potential as a commercial quarantine treatment for navel orange in international trade.

Phytosanitary Cold Treatment of Spotted-Wing Drosophila, Drosophila suzukii (Diptera: Drosophilidae) in 'Campbell Early' Grape

The effects of cold storage temperature and exposure duration on different developmental stages of spotted-wing drosophila (SWD) Drosophila suzukii (Diptera: Drosophilidae) on 'Campbell Early' grapes were examined to establish a phytosanitary control method. The immature stages (eggs, larvae and pupae) of SWD were all dead after a 6-d cold treatment at 1°C and 8-d cold treatment at 1.5 and 2°C. Probit-9 estimated a fourfold increase in cold treatment duration to achieve 99.9968% mortality, compared with the observed mortality. Efficacy tests using pupae, which were the most cold-tolerant stage, confirmed the validity of the selected temperature and exposure durations. Based on these results, 1°C, which requires a shorter exposure for complete mortality, was selected for the test in conditions that mimic those of grape exportation. Six-day cold treatments at 1°C produced 99.57%, mortality in different replicates, although the surviving pupae died later. Conversely, the 8- and 10-d treatments at 1°C showed 100% mortality, suggesting that these treatments can provide quarantine security against infestations of SWD on exported Campbell Early grapes, although an additional experiment with an increased sample size is required for further reliable conclusion.

Evaluation of Low-Temperature Phosphine Fumigation for Control of Oriental Fruit Fly in Loquat Fruit

Oriental fruit fly, Bactrocera dorsalis (Hendel; Diptera: Tephritidae), is recognized as a quarantine pest and a threat to Chinese loquat (Eriobotrya japonica Lindl.) fruit exports. Since loquat fruit is very sensitive to methyl bromide (MB) fumigation and cold treatment, in this study, low-temperature phosphine (PH3) fumigation was investigated to develop an alternative phytosanitary treatment method. Tolerance tests showed that the third instar was the most tolerant of all life stages of B dorsalis to PH3 gas at 8°C. Toxicity assay with 500-3000 ppm PH3 and subsequent probit analysis showed that 2000 ppm PH3 was optimal for fumigation and 152.75 h of treatment duration were required to achieve 99.9968% mortality. In the verification test, 144 and 168 h of treatment duration with 2000 ppm PH3 completely killed 35,277 and 35,134 B. dorsalis third instars, respectively. However, 13 live larvae were found after 120 h of treatment. Furthermore, these treatments reduced fruit respiration rates while causing no adverse effects on other fruit quality parameters, including firmness, soluble solid content, and titratable acidity over 192 h storage at 8°C. The results strongly suggest that low-temperature PH3 fumigation could be used for the postharvest control of B. dorsalis in loquat fruit.

Relative Tolerance of Six Bactrocera (Diptera: Tephritidae) Species to Phytosanitary Cold Treatment

To compare relative cold treatment tolerance across the economically important tephritid fruit flies (Diptera: Tephritidae), Bactrocera carambolae Drew & Hancock, Bactrocera correcta (Bezzi), Bactrocera cucurbitae (Coquillett), four populations of Bactrocera dorsalis (Hendel), Bactrocera zonata (Saunders), and Bactrocera tryoni (Froggatt), eggs (in vitro), and larvae (in infested fruit or on carrot diet) were cold treated at 2.0 ± 0.2 °C for selected durations. The study was performed to assess whether a single (i.e., generic) cold treatment could be developed that would control the entire group of fruit flies that were tested. Probit regression models showed that the hierarchy of cold resistance was third-instar larvae reared on carrot diet > third-instar larvae reared on orange > eggs test in vitro. Differences in mortality responses of third-instar larvae reared in oranges across populations of B. dorsalis were observed only at subefficacious levels of control. The majority of Bactrocera species responded the same at the high levels of control demanded of phytosanitary treatments, which indicated that cold treatments would be similarly effective across the species and populations tested. B. cucurbitae was found to be the most cold tolerant of all the species tested.

Assessment of Navel Oranges, Clementine Tangerines, and Rutaceous Fruits as Hosts of Bactrocera cucurbitae and Bactrocera latifrons (Diptera: Tephritidae)

Export of Citrus spp. fruits may require risk mitigation measures if grown in areas with established tephritid fruit fly (Diptera: Tephritidae) populations capable of infesting the fruits. The host status of Citrus spp. fruits is unclear for two tephritid fruit fly species whose geographic ranges have expanded in recent years: melon fly, Bactrocera cucurbitae (Cocquillett), and Bactrocera latifrons (Hendel). In no choice cage infestation studies, B. latifrons oviposited into intact and punctured Washington navel oranges (Citrus sinensis [L.] Osbeck) and Clementine tangerines (C. reticulata L. var. Clementine), but eggs rarely developed to the adult stage. B. cucurbitae readily infested intact and punctured tangerines, and to a lesser extent punctured oranges, but did not infest intact oranges. Limited cage infestation and only a single literature report of field Citrus spp. infestation suggest that risk mitigation of Citrus spp. for B. latifrons is not needed. Risk mitigation options of Citrus spp. for B. cucurbitae, including heat and cold treatments and systems approaches, are discussed.