Conant, Patrick

Proceedings of the Hawaiian Entomological Society

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Vol. 31, December 31,1992 91Banana Bunchy Top Disease, a NewThreat to Banana Cultivation in Hawaii1PATRICK CONANT*Symptoms of banana bunchy top disease (BBTD) were first recognizedin Hawaii at Punaluu, Oahu by F. Cruz (personal communication) in July1989. The presence of this virus disease was subsequently confirmed by R.Dietzgen (personal communication) of the Department of Primary Industries, Queensland, Australia, using monoclonal antibodies, developed inTaiwan (Su and Wu 1989), in an enzyme-linked immunosorbent assay(ELISA). This disease was a new Hawaii State Record.WORLD DISTRIBUTION OF BBTDBunchy top disease was first reported in Fiji in 1889, and is believed tohave been imported there with plants from Tanna, New Hebrides, about1886 (Simmonds 1931). The virus is probably endemic to Southeast Asia,but is now known to occur in Egypt, Australia, India, Taiwan, Congo, SriLanka, Antilles, Papua New Guinea, New Caledonia, Canary Islands, Philippines, Guam, Samoa, Tonga, Saipan, Tinian, Kiribati, Northern MarianaIslands, Tuvalu, and other Pacific island groups (Stover 1972).BBTD is a systemic disease that can infect all species of Musa. There isno known cure for infected plants and all propagative parts of the plantwill become infected. The virus is only known to be transmitted by thebanana aphid, Pentalonia nigronervosa Coquerel, which has been known tobe established in Hawaii since 1924, but was probably here earlier (Zimmerman 1948). The source of the virus found in Hawaii is unknown, but itprobably came with infected plant material smuggled into the state.SYMPTOMSRecognition of the symptoms of BBTD is crucial to its control. Certain"key" symptoms, easily visible with the naked eye, allow rapid field diagnosisthat can be quite reliable if done by trained inspectors. The most obviousof these is the "bunching" of die terminal leaves; this is also referred to as"strangles," "curly top," and "cabbage top" (Fig. 1). Poor development ofthe young petioles produces a rosette appearance. The apical leaves areerect, narrow, and brittle when crushed in the hand. Leaf margins may alsoappear "wavy" and yellow.Undersides of petioles of infected plants often exhibit dark green longitudinal streaks. Symptoms of the leaf veins are best viewed from theunderside in direct sunlight. Leaf veins proximal to the midrib are dark■Presidential address presented at the December 1989 HES meeting.-Hawaii Deparment of Agriculture. 1428 S. King Street, Honolulu, Hawaii 96814.92 Proceedings, Hawaiian Entomological SocietyFIGURE 1. A mat of banana plants in Waimanalo showing typical symptoms of bananabunchy top disease.FIGURE 2. Stunted fruit on a banana plant infected with lianana bunchy top disease.Vol. 31, December 31,1992 93green; thus, in many cases, they can be seen extending into the white areaalong the midrib. This symptom is known as "hooking." In healthy plants,this area of the midrib is normally free of blemishes. Veins in the centralarea of the leaf may also be darkened intermittently, producing an appearance like written Morse Code.Fruits produced by infected plants will usually be stunted and may notemerge completely from the leaf cluster at the top of the pseudostem (Fig.2). Plants infected when they are very young may not produce fruit at all.DISTRIBUTION OF BBTD ON OAHUSince the original detection of BBTD in Punaluu, Oahu, many infectedplants from residential areas throughout Honolulu, and from two farms inwindward Oahu at Waimanalo and Kahaluu, had been reported (Fig. 3),as of December 19, 1990. It should be noted that the three discoveries atHawaii Kai, Makakilo, and Pearl City appear to be isolated cases of plantingsof previously infected plants, rather than cases where existing plantingswere infected by aphids from nearby infected plants. Infected banana matsfound in other residential areas all had other infected mats in their vicinities. These areas include Pacific Heights, Alewa Heights, Kalihi, Liliha,Nuuanu, Pauoa, Papakolea, Punchbowl, Manoa, Kapahulu and KaimukiFIGURE 3. Distribution of banana plants on Oahu found to be infected with bananabunchy top disease as of December 19, 1990. Darker dots indicate threeisolated sites where infected planting material was probably used.94 Proceedings, Hawaiian Entomological Society(Fig. 3). The rather shocking news of the wide distribution of BBTD suggests that the disease has been on Oahu for at least a few years. Knowledgeof the biology of its vector, the banana aphid, will help to explain the spreadof this disease.BANANA APHID, THE VECTORPenlalonia nigronervosa is the only known vector of BBTD according toWaterhouse and Norris (1987). These authors provide detailed informationon the biology of this insect, which I have summarized here. The speciesis parthenogenetic and viviparous. Adults are known to produce about twoyoung per day and may produce up to 50 offspring in their lifetimes. Eachof the four nymphal instars lasts 2 to 4 days. The life span of adults rangesfrom 27 to 37 days. Alate females may not be produced in new coloniesuntil after 7 to 10 generations of apterae. In regions without cool winters,up to 30 generations, with four lots of alatae, may be produced per year.The aphids cluster on the terminals of suckers and larger plants (usuallyin lower numbers), and also at the base of the pseudostem, as deep as 7 to8 cm below the soil. They may also be found on the fruit. Ants are knownto be associated with this aphid in Hawaii, apparently to collect honeydew.Nymphs are known to be better vectors of BBTD than adults. They requirea minimum of 17 hours feeding time to become infective and must feedfor 1.5 to 2 hours to infect a healthy plant. A newly infected plant will beginto show symptoms about one month after infection. Genera with speciesknown to be alternate hosts of this aphid (Waterhouse and Norris 1987)that grow in Hawaii include Alpinia, Heliconia, Zingiber, Hedychium, Phaeome-ria, Cobcasia, Lycopersicon, Strelitzia, Alocasia, Arum, Amomum, Costus, Cala-dium, Calla, Dieffenbachia, Eletlaria, Ravenala, and Opuntia, and several ferns.BBTD CONTROL METHODSThere are several methods that have been, or can be, used to try tocontrol the spread of BBTD. In Hawaii, an inter-island quarantine wasobviously the most important first step. A 120-day interim quarantine ondie movement of banana plants from Oahu was put into effect by theHawaii Department ofAgriculture (HDOA) until a permanent quarantinecan be established. Physical removal of infected mats by grubbing is a verylabor intensive method ofcontrol that is effective in small plantings. Largerfarms require heavy equipment to use this technique effectively. The HDOAis presently roguing infected mats by grubbing in residential and waysideareas. Periodic inspections of farms are made and infected mats are markedfor the farmers to rogue. This technique has been used to control BBTDsuccessfully in other countries such as Australia (Allen 1975). Stover (1972)states, "Without a bunchy top control programme, bananas cannot begrown on a commercial scale. In peasant agriculture, with small holdings,however, an effective programme is difficult to enforce and it is likely thatbunchy top will continue to cause serious losses."Vol. 31, December 31,1992 95A more efficient method of roguing is through the use of herbicides.Beaver (1982) reported relatively rapid kill of infected mats with picloramin Guam. Wooden pins impregnated with 6 mg of picloram were pressedinto the pseudostem, using four or fewer pins per pseudostem. Mats werekilled within 21 days using this technique. Regupathy (1980) reportedcomplete kill of mats with 2,4 — Dichlorophenoxyacetic acid. The HDOAhas begun preliminary tests of chemical roguing techniques to determinetheir suitability for farms and residential areas in the state.Control of the vector is an indirect method of controlling BBTD but itis nonetheless important. A quarantine exemption under Section 18 of theFederal Insecticide Fungicide and Rodenticide Act was granted for farmersto use diazinon on banana trees for aphid control until September 30,1990.Use of this chemical as a long term chemical control method is beingconsidered by HDOA. Control of ants around the mats of bananas is alsoadvisable since ants have been implicated in the movement of aphids andin protecting them from natural enemies (Hely et al. 1982).Biological control of P. nigronervosa is also being seriously considered.One recorded parasite of this aphid is already present in Hawaii, but hasnever been reared from the aphid here. This is the aphidiid wasp, Lysiphle-Inis lestaceipes (Cresson), which is known to attack other species of aphidsin Hawaii (B. Kumashiro, personal communication). Waterhouse and Nor-ris (1987) list the known natural enemies of P. nigronervosa. Most of theseare non-specific predators, but at least one species of Aphidius (A. colemaniViereck) was considered "worth attention." The HDOA has initiated exploration in Southeast Asia for natural enemies of P. nigronervosa. All naturalenemies sent to Hawaii will be given host specificity tests under quarantineconditions and results will be reviewed by advisory committees of the Boardof Agriculture prior to any releases.LITERATURE CITEDAllen, R.N. 1975. Bunchy Top of Bananas. Biology Branch Plant Disease Bulletin 54. NewSouth Wales Department of Agriculture 6 p.Beaver, G.R. 1982. Use of picloram for eradication ofbanana diseased with bunchy top. PlantDisease 66:906.Hely, P.C., G. Pasfleld and/G CeUatley. 1982. Insect Pests of Fruit and Vegetables in NewSouth Wales. Inkata Press. Melbourne, Australia 312 p.Rcgupathy, R. 1980. Studies on the use of encapsulated pesticides for control of bunchy topdisease. Madras Agric. J. 67:741.Simmonds, H.W. 1931. Noxious weeds and their control in Fiji. II Biological control. FijiAgricultural Journal 4:29.Stover, R.H. 1972. Banana Plantain and Abaca diseases. Farnham Royal, U.K. CAB 316 p.Su, H.J. and R.Y. Wu. 1989. Characterization and Monoclonal auti!x)dies of the Virus CausingBanana Bunchy Top. Food and Fertilizer Technology Center. Technical BulletinNo. 115.Waterhouse, D.F. and K.R. Norris. 1987. Biological Control, Pacific Prospects. Inkata PressMelbourne viii + 454 p.Zimmerman, E.C. 1948. Insects of Hawaii. Volume 5. Homoptcra Slcrnorhyncha. Universityof Hawaii Press, Honolulu. 464 p.96 Proceedings, Hawaiian Entomological Society

Banana Bunchy Top Disease, a New Threat to Banana Cultivation in Hawaii

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Banana Bunchy Top Disease, a New Threat to Banana Cultivation in Hawaii

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