The mango seed weevil, Cryptorhynchus mangiferae (F.), has prevented the export of mangoes from Hawaii to the U.S. mainland for over 50 years because there were no approved quarantine treatments to control this pest. Irradiation was explored as a method to prevent adult emergence in, or to sterilize, mango seed weevil. Mixed-age mango seed weevils in mangoes were irradiated with target doses of 50, 100, or 300 Gy and held for adult emergence. The 300 Gy treatment (dose range 180–310 Gy) did not prevent adult emergence. Emerging adults from the 100 and 300 Gy treatments were lethargic and short-lived, and laid no eggs indicating sterility. An irradiation quarantine
treatment (100 Gy) to sterilize mango seed weevil in mangoes has been proposed. Approval of this treatment will open U.S. mainland markets to mango exports from Hawaii

Follett, Peter A.

Proceedings of the Hawaiian Entomological Society

ScholarSpace at University of Hawai'i at Manoa

IRRADIATION FOR MANGO SEED WEEVIL 85Irradiation as a Quarantine Treatmentfor Mango Seed WeevilPeter A. FollettUSDA, ARS, U. S. Pacific Basin Agricultural Research Center,PO Box 4459, Hilo, Hawaii 96720Abstract: The mango seed weevil, Cryptorhynchus mangiferae (F.), has prevented theexport of mangoes from Hawaii to the U.S. mainland for over 50 years because therewere no approved quarantine treatments to control this pest. Irradiation was exploredas a method to prevent adult emergence in, or to sterilize, mango seed weevil. Mixed-age mango seed weevils in mangoes were irradiated with target doses of 50, 100, or300 Gy and held for adult emergence. The 300 Gy treatment (dose range 180–310 Gy)did not prevent adult emergence. Emerging adults from the 100 and 300 Gy treatmentswere lethargic and short-lived, and laid no eggs indicating sterility. An irradiation quar-antine treatment (100 Gy) to sterilize mango seed weevil in mangoes has been pro-posed. Approval of this treatment will open U.S. mainland markets to mango exportsfrom Hawaii.Key words: Cryptorhynchus mangiferae, Sternochetus mangiferae, disinfestation,postharvest treatmentIntroductionWith the demise of the sugarcane industry in Hawaii in recent years, vast acreages havebecome available for diversified agriculture. A tropical exotic fruit industry is rapidly ex-panding to help fill the void and is expected to be an important part of Hawaii’s crop diver-sification. An important step in this expansion is the development of quarantine treatmentsto permit exports. Currently, irradiation is an accepted quarantine treatment for export ofpapaya, carambola, lychee, rambutan, longan, atemoya, sapodilla, and abiu from Hawaii tothe U. S. mainland. Irradiation quarantine treatments up to this time have been developedexclusively for fruit flies. In addition to fruit flies, many other insect and mite pests areclassified as regulatory pests and their appearance has equal status with fruit flies in inter-rupting export shipments.The mango seed weevil, Cryptorhynchus (=Sternochetus) mangiferae (F.), first reportedin Hawaii in 1905 (Kotinsky 1905), is a federally quarantined pest that has prevented theshipment of mangos from Hawaii into the continental United States for over 50 years(Armstrong 1993). Pest control research for mango weevil over the years has looked at anumber of options, including field sanitation, chemical sprays (trunk and foliar), naturalenemies (parasitoids, the fungus Beauvaria bassiana), host plant resistance, and x-ray fruitculling technology with little success (Hansen and Armstrong 1990, Hansen 1991, CABand EPPO 1997, Pena et al. 1998). Therefore, the industry must depend on a postharvestdisinfestation treatment. Postharvest researchers have attempted to kill mango seed weevilin mangoes, while maintaining fruit quality, using heat, cold, and fumigation treatmentswithout success (Balock and Kozuma 1964). Irradiation is a viable alternative to disinfestmangoes of mango seed weevil.A typical quarantine treatment for fruit flies is developed by testing hundreds of thou-sands of lab-reared insects, which are artificially inoculated into the fruit, so-called probit 9PROC. HAWAIIAN ENTOM L. SOC. (2001) 35:85–9086 FOLLETT(99.9968% mortality) level testing. Development of an irradiation quarantine treatment formango seed weevil has been difficult because there is only one generation of weevils peryear, and no artificial diet exists to culture the insect in the laboratory. Therefore, probit 9level testing is impractical. Instead, we pursued an alternate approach: to generate data foran irradiation treatment with the numbers of insects available, and to show that the weevilwould have no economic impact on fruit production and negligible impact on mangogermplasm if it were introduced into the U.S. mainland (Follett 2000, Follett and Gabbard2000). If the risk of mango seed weevil could be put in perspective, regulators could beconvinced that a safe quarantine treatment could be developed by testing only a few thou-sand insects. In this paper, I present the evidence for an effective irradiation quarantinetreatment to disinfest mangoes of mango seed weevil.BackgroundStudies on irradiation against mango seed weevil in Hawaii date back 40 years. Upadhyaand Brewbaker (1966) irradiated approximately 100 infested fruits at each of four doses(300, 600, 900 and 1,200 Gy) and measured survival of adult weevils after 3 and 5 weeks.About 70% of mangoes treated with an irradiation dose of 300 Gy produced live but mori-bund adults, and no adults survived doses of >600 Gy after 5 weeks. The authors state thatthe adult stage is the most tolerant to irradiation but provide no data.In the early 1970s, Seo et al. (1974) conducted a series of irradiation experiments withmango seed weevil in Hawaii, examining effects on mango seed weevil mortality and steril-ity. Irradiation treatment with a dose of 329 Gy killed all 1,143 weevils of mixed age infest-ing packaged mangoes. When the fruit density (number of fruit per fiberboard container)was varied at an irradiation dose of 206 Gy, 4 out of 1,324 adults survived at the highestdensity (3.92 g/cm2), 1 out of 1,206 at the middle density and 0 out of 1,206 at the lowestdensity (2.56 g/cm2). Adults from untreated control fruit remained alive after 6 months. Toexamine sterility, 30 mating pairs in individual glass vials were treated with a dose of 50,75, 100 or 200 Gy, or left untreated as controls. Twenty-nine females survived treatmentwith 50 or 75 Gy (21 and 8 respectively) and laid a total of 18 sterile eggs. All sixty of thefemales irradiated with 100 or 200 Gy died without producing eggs. Seventeen untreatedfemales produced 1,175 eggs of which 639 hatched.In Australia in the late 1980s, 1,956 ‘Kensington’ mangoes, with a natural mango seedweevil infestation estimated as 1,065 (54.6%) larvae, 725 (37.2%) pupae, and 161 (8.3%)adults, were irradiated at 300 Gy (Heather & Corcoran 1992) The 300 Gy treatment wasselected based on the results of Seo et al. (1974) (N. Heather personal communication). The300 Gy treatment prevented adult weevil emergence from the mangoes and resulted in100% mortality after 8 months. By comparison, 522 control fruit with a natural infestationconsisting of an estimated 32 larvae (6.5%), 354 pupae (71.7%), and 108 adults (21.9%)produced 110 surviving adults after 8 months.In South Africa, Thomas (1975) reported that 500 Gy reduced adult emergence almost tozero but 750 Gy was required to completely inactivate the weevil and prevent emergence.Milne et al. (1977) measured direct mortality to all life stages and prevention of emergenceof the adult weevils with early- and late-maturing varieties of mangoes irradiated at dosesfrom 300–850 Gy. After irradiation, seeds containing weevils were checked weekly for 6weeks. In the early maturing variety, 60% of the population was in the adult stage; in thelate-maturing variety 80% of the population was in the adult stage. According to the au-thors, preliminary studies indicated that adult weevils were, by far, the most tolerant stage.Irradiation doses of 300 and 375 Gy were inadequate in preventing adult emergence fromfruit, particularly in the late-maturing cultivar where a larger proportion of the populationIRRADIATION FOR MANGO SEED WEEVIL 87was in the adult stage. At 500 Gy, one adult emerged from the seed but died soon afterward.In seeds treated with 500 Gy or more, adults inside the seed that were alive appeared mori-bund and incapable of emerging. No tests were conducted to determine sterility of adults atvarious irradiation doses. More recent work suggests a dose of 600 Gy is required to pre-vent mango seed weevil emergence from fruit under South African conditions (L. Milne,personal communication).In India, Shulka and Tandon (1985) irradiated mango seed weevils in harvest-mature‘Alphonso’ mangoes at 10, 100, 200, 300, 400, and 500 Gy. Fruit were cut open after anunspecified period to examine the presence of dead or live insects. The 500 Gy dosagekilled immature stages but not adults.Different treatment dose intervals, dosimetry, methods, and mango cultivars used in eachof the irradiation studies discussed above make it difficult to draw general conclusions aboutan effective irradiation dose for mango seed weevil (Table 1). Based on the studies of Seo etal. (1974) and Heather and Corcoran (1992), an irradiation dose of 100 Gy is adequate tosterilize mango seed weevil and 300 Gy will usually prevent adult emergence. Studies byThomas (1975) and Milne et al. (1977) suggest a higher dose is required to prevent adultemergence in South Africa. Research in South Africa has focused on obtaining a quicker killbecause, in late season, mango seed weevils occasionally emerge from the ripening fruit onthe tree (Heather 1992). This event is unlikely under conditions in Hawaii and Australia withearly and mid-season mango varieties, where weevils typically emerge from fruit only afterthe flesh has decayed on the ground and the seed is exposed. Consequently, it is more diffi-cult to prevent some emergence of weevils with irradiation in South Africa.Table 1. Reported irradiation doses to disinfest mangoes of mango seed weevil.Irradiation dose (Gy)Prevent adult CauseStudy Country  emergence sterilityUpadhya &Brewbaker 1966 USA/Hawaii 300 —Seo et al. 1974 USA/Hawaii 329 50z100 yHeather &Corcoran 1992 Australia 300  —Thomas 1975 South Africa 750 —Milne et al. 1977 South Africa >500 —Shukla andTandon 1985 India >500 —zIrradiated adults laid eggs but none hatched.yIrradiated adults died without laying eggs.88 FOLLETTWe conducted studies from 1997 to 1999 to confirm the results of irradiation treatmenttests reported by other researchers.Materials and MethodsHarvest-mature ‘Haden’ mangoes were collected from the Yamada orchard in Kalapana, HIin 1998, and infestation was determined based on oviposition scars. Infested mangoes weretransported to the Hawaii Research Irradiator (HRI) at the University of Hawaii at Manoaand irradiated at target doses of 50, 100, or 300 Gy, or left untreated as controls. The HawaiiResearch Irradiator uses a 60Co source of gamma radiation and the dose rate at the time ofthe tests was 5.3–5.8 Gy min–1. Details on dose mapping, dosimetry, and dose variation aregiven in Follett and Lower (2000). A sub-sample of fruit was taken beforehand and openedto determine the age structure of weevils in the infested fruit. After irradiation, the fruitflesh was cut away and the seeds in their husks were held over an 8-month period andinspected weekly for adult emergence. Emerging adults were placed in screen cages withimmature mango fruits to examine reproduction. The experiment was replicated 4 timesand all emerging adult weevils for a given irradiation treatment (control, 50, 100, 300 Gy)were held in one cage.ResultsAlthough adult emergence occurred at all irradiation doses, emergence was reduced inirradiated fruits (Table 2). The 300 Gy treatment did not prevent adult emergence, unlikeprevious studies in Hawaii and Australia. This is probably explained by dose variation inthe treatment chamber: the dose uniformity ratio when using the full volume of the chamberat HRI is 1.6 to 1.8, with the dose distribution skewed toward lower doses (see Follett andLower 2000). Therefore, the dose range of the 300 Gy treatment was estimated to be 180–315 Gy, and many individuals received a radiation dose less than 300 Gy.Emerging adults from the 100 and 300 Gy treatments were lethargic and short-lived, andno eggs were laid indicating sterility. Egg laying by untreated control weevils was consis-tent but at a relatively low rate compared with weevils in the study by Seo et al. (1974). Thissuggests that cage conditions in our studies were not ideal for mating and/or oviposition.Nonetheless, sterility was achieved in this study with an irradiation dose of 100 Gy (esti-mated dose range, 60–105 Gy), as it was in the study by Seo et al. (1974) (Table 2).Table 2. Effect of irradiation on adult emergence and sterility in mango seed weevil.Dose Fruits Adults Adults Eggs layed Hatched(Gy) treated emerged dead in seed0 255 160  9 190  3750 330  95 23 57 15100 331  61 15 0 0300 335  53 49 0 0Age structure at treatment: 39% early larvae, 19% late larvae, 18% pupae, and 24% adults.IRRADIATION FOR MANGO SEED WEEVIL 89DiscussionMango seed weevil is monophagous and requires mango to complete development. Eggsare laid on the surface of young fruit and neonates burrow down to the developing seed;larvae feed within the seed, which becomes encased in a tough fibrous husk, and develop-ment to the adult stage occurs entirely in the seed (Balock and Kozuma 1964, Follett andGabbard 2000). Therefore, mango seed weevil attack usually goes unnoticed and does notreduce fruit marketability.The mango industry on the U. S. mainland is small and concentrated in southern Florida.Florida’s mango industry focuses on growing mango for seed production in nurseries andorchards. The high-risk quarantine pest status given to mango weevil is mainly in responseto concerns from the mango industry in Florida that C. mangiferae infestation would reduceseed germination and therefore limit seed production in nurseries and orchards (Balock andKozuma 1964). Recent studies suggest that infestation of, and damage to, mango seeds bymango seed weevil does not adversely affect seed germination as previously thought (Follett2000, Follett and Gabbard 2000). Therefore, mango seed weevil is not a high-risk pest interms of its potential impact on Florida’s mango industry. Nevertheless, mango seed weevilis a pest and may cause some crop loss due to premature fruit drop and damage to fruit pulp,albeit rarely (Follett and Gabbard 2000).Our irradiation data were submitted to USDA-APHIS for a quarantine treatment alongwith data from field studies showing that mango seed weevil is a less serious pest of man-goes than previously thought (Follett and Gabbard 2000). A proposed rule was published inthe Federal Register on May 26, 2000 recommending an irradiation dose of 100 Gy tocontrol mango seed weevil in exported mangoes. Publication of the final rule for the irra-diation quarantine treatment will be the first time that irradiation has been approved for aninsect other than a fruit fly. This will open U.S. mainland markets to mango exports fromHawaii.AcknowledgmentsI appreciate the efforts of Zona Gabbard and Bob Lower in carrying out this research.Logistical support from Weston and Keith Yamada and Luellen and Kelly Greenwell is alsogreatly appreciated.ReferencesArmstrong, J. W. 1993. Research on quarantine disinfestation of mangos. p. 10–12 In Proceedings:Conference on Mango in Hawaii. University of Hawaii, Honolulu, Hawaii.Balock, J. W., and T. T. Kozuma. 1964. Notes on the biology and economic importance of the mangoseed weevil, Sternochetus mangiferae (Fabricius), in Hawaii (Coleoptera: Curculionidae). Proc.Hawaiian Entomol. Soc. 18: 353–364.CAB and EPPO. 1997. Sternochetus mangiferae. p. 526–531 In Quarantine Pests for Europe. CABInternational, Wallingford, UK.Follett, P. A. 2000. Mango growers—fear no weevil. Agriculture Hawaii 1 (4): 24–25.Follett, P. A. and Z. Gabbard. 2000. Effect of mango weevil (Coleoptera: Curculionidae) damage onmango seed viability. J. Econ. Entomol. 93: 1237–1240.Follett, P. A. and R. A. Lower. 2000. Irradiation to ensure quarantine security for Cryptophlebia spp.(Lepidoptera: Tortricidae) in sapindaceous fruits from Hawaii. J. Econ. Entomol. 93: 1848–1854.Hansen, J. D. 1991. Mango weevil biology, field control, and postharvest technology: a review. Intern.J. Trop. Agric. 9: 234–244.Hansen, J. D., and J. W. Armstrong. 1990. The failure of sanitation to reduce infestation by themango seed weevil, Cryptorhynchus mangiferae (F.), (Coleoptera: Curculionidae). Tropical PestManagement 36: 359–361.90 FOLLETTHeather, N. W. 1992. Review of irradiation as a quarantine treatment for insects other than fruit flies.p. 203–218 In Panel Proceedings of the Final Research Coordination Meeting on “Use of Irradiationas a Quarantine Treatment of Food and Agricultural Commodities”, Kuala Lumpur, Malaysia, Aug.1990. IAEA, Vienna.Heather, N. W., and R. J. Corcoran. 1992. Effects of ionizing energy on fruit flies and seed weevil inAustralian mangoes. p. 43–52 In Panel Proceedings of the Final Research Coordination Meeting on“Use of Irradiation as a Quarantine Treatment of Food and Agricultural Commodities”, Kuala Lumpur,Malaysia, Aug 1990. IAEA, Vienna.Kotinsky, J. 1905. Notes and exhibitions. Haw. For. Agric. 2: 266.Milne, D. L., L. B. Kok, A. C. Thomas, and D. H. Swarts. 1977. Inactivation of mango seed weevil,Sternochetus mangiferae, by gamma irradiation. Citrus and Subtrop. Fruit J. 518: 11–17.Mitchell, W. C. 1993. Fruit flies and mango seed weevil in relation to quarantine. p. 5–9 In Proceed-ings: Conference on Mango in Hawaii. University of Hawaii, Honolulu, Hawaii.Pena, J. E., A. I. Mohyuddin, and M. Wysoki. 1998. A review of the pest management situation inmango agroecosystems. Phytoparasitica 26: 129–148.Seo, S. T., R. M. Kobayashi, D. L. Chambers, L. F. Steiner, C. Y. L. Lee, and M Komura. 1974.Mango seed weevil: Cobalt-60 gamma irradiation of packaged mangoes. J. Econ. Entomol. 67:504–505.Shukla, R. P. and P. L. Tandon. 1985. Bio-ecology and management of the mango weevil, Sternochetusmangiferae (Fabricius) (Coleoptera: Curculionidae). Intern. J. Trop. Agric. 3: 293–303.A.C. Thomas. 1975. Gamma irradiation—An answer to the mango grower’s prayer. Intern. Proj. in theField of Food Irradiation (South Africa) 5: 9–18.Upadhya, M. D., and J. L. Brewbaker. 1966. Irradiation of mangoes for control of the mango seedweevil. Hawaii Farm Science 15 (1): 6–7, University of Hawaii Cooperative Extension Service.

Irradiation as a Quarantine Treatment for Mango Seed Weevil

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Irradiation as a Quarantine Treatment for Mango Seed Weevil

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