AN ATTEMPT AT THE ERADICATION OF THE ORIENTAL FRUIT FLY, Bactrocera dorsalis (HENDEL) FROM MAURITIUS

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1 AN ATTEMPT AT THE ERADICATION OF THE ORIENTAL FRUIT FLY, Bactrocera dorsalis (HENDEL) FROM MAURITIUS S I Seewooruthun, P Sookar, S Permalloo, A Joomaye, M Alleck, B Gungah and A R Soonnoo Ministry of Agriculture, Fisheries and Co-operatives ABSTRACT The Oriental Fruit Fly, Bactrocera dorsalis was detected for the first time in Mauritius in June It is recognised as one of the most destructive fruit fly pests in the world. Timely detection of this serious pest prompted the adoption and application of measures to contain B. dorsalis with a view to its eradication. The main methods of control used are the Bait Application and Male Annihilation Techniques. B. dorsalis is presently contained within an area of about 150 km 2 in the south of Mauritius. Measures are being continued in order to achieve eradication. INTRODUCTION A few species of fruit fly (Diptera, Tephritidae) pests of fleshy fruits and vegetables have existed in Mauritius for several decades. Other species have been accidentally introduced since the early 1950's. The Natal Fly, Ceratitis rosa, was recorded in 1953 and displaced the existing Ceratitis capitata (Orian and Moutia 1960). Bactrocera zonata was detected in 1987 (MAFNR 1987), and in turn, displaced C. rosa, to become the most economically important fruit fly of fleshy fruits (MAFNR 1990).This phenomenon has been observed in other countries where introduced species have displaced existing ones. In India, B. dorsalis and B. zonata have reduced Ceratitis capitata to insignificant levels (Kapoor and Grewal 1986). Another exotic species, Carpomya vesuviana, which is specific to jujube, was recorded in Mauritius in 1986 (MAFNR 1986). All the introduced species are now part of the Mauritian fruit fly complex. The Oriental Fruit Fly, Bactrocera dorsalis, was detected for the first time in Mauritius, on 5 June 1996 (MAFNR 1996). A single female fly was collected at Camp Carol, a village about one kilometre from the airport, in a McPhail trap baited with ammonium chloride. This early detection was due to the fact that traps have been placed throughout the island, in the context of an area wide programme for the control of fruit flies (Soonnoo et al. 1995; Permalloo et al. 1997). The control programme, funded jointly by the European Union and the Government of Mauritius, is operational in the North and North East of the island, and also includes research and quarantine. Traps have thus been set to cover the island for monitoring of adult populations, at port and airport for surveillance and at different sites for experimentation. After the first detection, the fly was sent to the International Institute of Entomology for confirmation. A series of actions were applied in the village of Camp Carol, the main ones being the Bait Application Technique (BAT) and the Male Annihilation Technique (MAT). Subsequently, B. dorsalis was again recorded in low numbers as from 18 July 1996 in other regions in the Southern districts of Mauritius. 211

2 Rationale for Attempting Eradication B. dorsalis is recognised as one of the most damaging fruit fly pests in the world, especially due to its very wide host range, high reproductive potential, high mobility and adaptability to climate. Its presence in Mauritius is the first record from the African region and its establishment in Mauritius would be a serious threat to nearby countries. The occurrence of B. dorsalis in Mauritius is an obstacle for the promotion of export of fruits and vegetables. In fact, a ban was imposed on the exportation of small green chillies to Réunion Island. This ban has very recently been lifted because the chilly production areas have been considered pest free due to the quarantine measures taken to contain B. dorsalis in a restricted area in the south of the island, a reasonable distance away. MATERIALS AND METHODS The two Southern districts, Grand Port and Savanne, comprise an area of about 420 km 2. As detection of B. dorsalis progressed to other villages of the South, the eradication area was extended to about 300 km 2,out of which about 10% was calculated to harbour probable host plants. Measures taken for the containment of B. dorsalis The main methods being used for the control and containment of B. dorsalis are the Bait Application and Male Annihilation techniques. BAT is directed at killing both male and female flies whereas MAT attracts and kills male flies through the use of parapheromones. Both methods are at present being used in the area wide programme to control fruit flies in the North and North East (Soonnoo et al. 1995; Permalloo et al. 1997). MAT has been successfully used for control (Cunnigham and Suda 1986) and eradication of B. dorsalis in a number of cases. Eradication with MAT was first achieved on Rota Island in 1963 (Steiner et al. 1965), and later in the Okinawa Islands in 1982 (Koyama et al. 1984). MAT has also been applied successfully together with sterile insect releases in the Mariana Islands (Steiner et al. 1970). Presently, BAT and MAT are being used in Australia in the eradication programme of the Papaya Fruit Fly, Bactrocera papayae from North Queensland (Jang et al. 1996). BAT has also been used in eradication programmes, on its own, or, in combination with other methods. BAT is frequently used to eradicate exotic species entering California, and bait applications are used with sterile releases for eradication of the Mexican Fruit Fly from California and the Medfly from Florida (CFDA 1994). BAT and sterile releases have also been used for the eradication of Queensland fruit fly, Bactrocera tryoni, from Adelaide, Australia ( Reynolds et al. 1995). For the present eradication programme of B. dorsalis, BAT and MAT are reinforced with other measures. BAT consists of applying spot sprays of 40 ml of a mixture of 2% protein hydrolysate and 0.7% malathion 57 EC in water, at the rate of 200 spots per hectare. Neutralised brewers waste is also being used instead of commercial protein hydrolysate (Permalloo et al. 1997). Each round of BAT is completed in seven days except in detection areas where it is reinforced and effected every four days for a period of one month. For the Male Annihilation Technique, plywood blocks (50mm x 50mm x 12mm) incorporated with about 6 g of 67% methyl eugenol and 1 g of malathion 57 EC are fixed onto the trunk of fruit or other trees at the rate of 10 to 14 per hectare. These blocks are being placed since July 1996, each round taking two to two and a half months. The frequency of both BAT and MAT has been increased in the eradication programme, as compared to the wide area control programme, for maximum efficacy and to keep the fly population under constant pressure. Other measures included in the eradication programme are: cover spray on, and soil drenching under, bearing fruit trees; fruit clean up which comprises collection of fallen fruits and their disposal in trenches - these are drenched with an insecticide and covered with soil. The help of the public, Sugar Estates and District Council was enlisted for intensive fruit collection and disposal. Fruit stripping, especially in the case of mangoes, was also carried out in certain public places. 212

3 The eradication area also includes certain regions which are inaccessible by road, such as along river banks and cliffs. These areas harbour large numbers of Indian almond trees which escape treatment. Following the detection of certain hot spots in May, aerial treatment with the bait/insecticide mixture was resorted to in the inaccessible areas in June A ULM aircraft was used for this purpose, and the bait mixture was disposed by two Micronair AU 7000, utilising only the variable restrictor unit and the anti droplet of the atomiser. Aerial disposal of MAT blocks was also effected. Evaluation Two methods are used for evaluation of the control measures, namely detection from traps, and rearing from samples of collected fruits. The traps used are a local version of the Steiner type and are baited with methyl eugenol. These were initially placed around detection points, according to the Australian Protocol (D Agric. 1992). A total of 367 traps have been set in the eradication area. Traps were checked daily for a period of five months since the first detection. They are now monitored twice a week except at detection points where checking is done daily for a month. In addition, about 95 McPhail traps baited with protein hydrolysate or ammonium chloride are also monitored in this area. Samples are taken daily from collected fruits in the eradication area and kept in the laboratory in the South, for determination of infestation by different species. The identification of the species is done at the adult stage. RESULTS Actual trap catches of B. dorsalis in the different regions of the eradication area are given in Table 1. Out of a total of 143 adult flies trapped, the majority were caught during period July to September The figures when converted to weekly catches, show a gradual decrease in numbers trapped between July and September 1996, and only two adults during period 27 September to date (Figure 1). The population of B. zonata has also been reduced to insignificant levels (Figure 2). Emergence of B. dorsalis from collected fruits was recorded from six samples of Indian almond and three samples of mangoes (Table 2). Over 20 species of host fruits have been collected, totalling about two million fruits (Table 3). 213

4 Table 1 Trap catches of adult Bactrocera dorsalis Date No of flies collected Beau Vallon Blue Bay Camp carol Chemin Grenier Deux Bras Grand Bel Air Gros Billot Gros Bois La Rosa l'escalier Mahebourg 5-Jun Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Aug Sep Sep Sep Sep Sep Sep Sep Sep Sep Mar May Total Mare d'albert Mare Tabac Mont Fertile Plaine Magnien Riche en Eau Rose Belle Sauveterre St Hubert Surinam Trois Boutiques Union Vale Total Table 2 Emergence of Bactrocera dorsalis from collected fruits Fruit Locality Fruits collected Pupæ Species emerged Date Numbers Sample Total number Start of emergence Bactrocera dorsalis Bactrocera zonata Indian Almond Trois Boutiques 23-Jul Aug Indian Almond Plaine Magnien 25-Aug Oct Indian Almond Sauveterre 4-Apr Apr Indian Almond Trois Boutiques 4-Apr Apr Indian Almond Sauveterre 16-Apr May Indian Almond Sauveterre 22-Apr May Mango Plaine Magnien 16-Oct Oct Mango Savinia 22-Nov Dec Mango L'Escalier 30-Nov Dec

5 Table 3. Emergence of different fruit fly species from collected fruits Fruit variety Number of fruits Pupae collected Sampled Bactrocera cucurbitae Bactrocera dorsalis Bactrocera zonata Ceratitis capitata Ceratitis rosa Dacus ciliatus Trirhithromyia cyanescens August 1996 to December 1996 Chilly (long) Chinese Guava (red) Cucurbits Guava Indian Almond Mango Papaya Peach Tomato January 1997 to May 1997 Carambole Chilly (long) Chilly (small) Chinese Guava (red) Chinese guava (yellow) Citrus Coeur de Boeuf 1 1 Cucurbits Fruit de Cythere Goyave de L'Inde Grenade 10 2 Guava Indian Almond Mango Massons Papaya Peach Pocpoc Pomme Jacquot Prune Tabac marron Tomato

6 Number of flies caught An attempt at the eradication of the oriental fruit fly, Bactrocera dorsalis ( Hendel) S I Seewooruthun et al. 50 Figure 1 Weekly trap catches of Bactrocera dorsalis in the eradication area Jan Jun-96 5-Sep Nov Feb May-97 1-Apr Jul Oct-96 9-Jan-97 3-Apr Jun-97 Figure 2 Weekly trap catches of Bactrocera zonata in Southern Region Number of flies caught per trap Jan Jun-96 1-Aug-96 4-Nov Jan Apr-97 1-Apr-96 8-Jul Sep Dec Mar Jun-97 DISCUSSION The methods used for the containment of B. dorsalis are giving positive results. The eradication area which covered about 300 km 2 initially, has been reduced to about 175 km 2, taking into consideration detection from traps and fruits for the last ten months. B. dorsalis has not, at any moment, dispersed outside the Southern districts. Both evaluation methods, i.e. trapping and breeding from fruit samples are used in the context of the area wide control programme mentioned earlier. A total of 657 traps are monitored fortnightly, and fruit samples are collected regularly. B. dorsalis has not been recorded from either traps or fruits outside the outbreak area. Certain hot spots have been noted in the 216

7 eradication area from time to time. However, this is a normal occurrence in eradication programmes due to the presence of very small populations, before the actual eradication is achieved. A Regional Fruit Fly Programme which includes research, extension and quarantine to back up national fruit fly programmes is operational in Mauritius, Réunion and Seychelles. It is funded by the European Union and the Government of each participating country. In the context of this programme, an action plan is being prepared so as to be ready to meet the challenge of any future incursions, in terms of material, technical and scientific resources. Quarantine procedures are also being harmonised so as to minimise risks of entry of exotic pests. ACKNOWLEDGEMENTS We are grateful to the Permanent Secretary, Chief Agricultural Officer and Principal Agricultural Officer (Crop), for permission to publish this paper; gratitude is expressed to the European Union, for co-funding the eradication programme. We are indebted to the staff and personnel of the Entomology Division, who have been involved in the eradication programme. We acknowledge the International Institute of Entomology for confirming the identity of B. dorsalis; the help of Sugar Estates, the District Council of Grand port/savanne, and the Securiclean Ltd. for fruit clean up. REFERENCES CALIFORNIA DEPARTMENT OF FOOD AND AGRICULTURE The exotic fruit fly eradication program using aerial application of malathion and bait. Final Programmatic Environmental Impact Report. State Clearinghouse Number US : California Department of Food and Agriculture, p CFDA see under California Department of Food and Agriculture CUNNINGHAM RT and SUDA DY Male Annihilation through mass-trapping of male flies with methyl eugenol to reduce infestation of Oriental Fruit Fly (Diptera:Tephritidae) larvae in papaya. Journal of Economic Entomology 79: D. Agric see under Department of Agriculture DEPARTMENT OF AGRICULTURE, SOUTH AUSTRALIA Pest Eradication Unit Manual, 52pp. JANG E, SMITH S and ARMSTRONG J Assessment of the Papaya Fruit Fly eradication program in North Queensland. Report of visit by scientific panel, November 1996, 14pp. KAPOOR VC and GREWAL JS Fruit flies and their host preference in India. Proceedings of the second International Symposium on Fruit Flies, Crete. KOYAMA J, TERUYA T and TANAKA K Eradication of the Oriental fruit fly (Diptera: Tephritadae) from the Okinawa Islands by a Male Annihilation method. Journal of Economic Entomology 77: MAFNR see under Ministry of Agriculture, Fisheries and Natural Resources 217

8 MINISTRY OF AGRICULTURE, FISHERIES AND NATURAL RESOURCES Annual Report of the Agricultural Services of the Ministry of Agriculture, Fisheries and Natural Resources. MINISTRY OF AGRICULTURE, FISHERIES AND NATURAL RESOURCES Annual Report of the Agricultural Services of the Ministry of Agriculture, Fisheries and Natural Resources. MINISTRY OF AGRICULTURE, FISHERIES AND NATURAL RESOURCES Annual Report of the Agricultural Services of the Ministry of Agriculture, Fisheries and Natural Resources. MINISTRY OF AGRICULTURE, FISHERIES AND NATURAL RESOURCES Annual Report of the Agricultural Services of the Ministry of Agriculture, Fisheries and Natural Resources ORIAN AJE and MOUTIA LA Fruit flies (Trypetidae) of economic importance in Mauritius. Revue Agricole et Sucrière de l' Ile Maurice 38: PERMALLOO S, SEEWOORUTHUN SI, SOONNOO AR, GUNGAH B, UNMOLE L and BOODRAM R An area wide control of fruit flies in Mauritius. ( In press. Paper presented at second annual meeting of agricultural scientists, Food and Agricultural Research Council, Mauritius). REYNOLDS T, BAILEY P, PEREPELICIA N and JESSOP A Integrated chemical and sterile fly release trial no.3 to eradicate Queensland fruit fly at Clarence Gardens. Adelaide, South Australia : Pest Eradication Unit, Primary Industries, 37pp. SOONNOO AR, SMITH ESC, JOOMAYE A, PERMALLOO S and GUNGAH B A large scale fruit fly control programme in Mauritius. p In : CHUA TH and KHOO SG eds. Problems and Management of Tropical Fruit Flies. Proceedings of a Workshop, University of Malaysia.. STEINER LF, HART WG, HARRIS EJ, CUNNINGHAM RT, OHINATA K and KAMAKAHI DC Eradication of the Oriental fruit fly from the Mariana Islands by the methods of Male Annihilation and Sterile Insect Release. Journal of Economic Entomology 63: STEINER LF, MITCHELL WC, HARRIS EJ, KOZUMA TT and FUJIMOTO MS Oriental fruit fly eradication by male annihilation. Journal of Economic Entomology 58 : COMMENTS Q. Given that the oriental fruit fly is of quarantine importance, did you consider restricting the movement of fruits from the South to other regions. A. This question was raised but it was difficult to put into practice. To counteract, cover sprays were carried out in the south for mangoes, to prevent reinfestation. 218