The sterile insect technique for control of the oriental fruit fly, Bactrocera dorsalis (Hendel), in mango orchards in Ratchaburi Province, Thailand

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1 Proceedings of 6th International Fruit Fly Symposium 6 10 May 2002, Stellenbosch, South Africa pp The sterile insect technique for control of the oriental fruit fly, Bactrocera dorsalis (Hendel), in mango orchards in Ratchaburi Province, Thailand M. Sutantawong 1, W. Orankanok 2, W.R. Enkerlin 3 *, V. Wornoayporn 4 & C. Caceres 4 1 Office of Atomic Energy for Peace, Thailand 2 Institute of Irradiation for Agricultural Development, Department of Agricultural Extension, Thailand 3 Insect Pest Control Section, Joint FAO/IAEA Division in Food and Agriculture, Wagramer Strasse 5, P.O. Box 100, A-1400 Vienna, Austria 4 Entomology Unit, FAO/IAEA Agriculture and Biotechnology Laboratory, Seibersdorf, Austria Fruit flies are the main constraint to improving production and trade of fruits and vegetables in Thailand. Therefore, since 1987, the Department of Agricultural Extension (DOAE) in cooperation with the Office of Atomic Energy for Peace has run a pilot project for control of the oriental fruit fly (OFF),Bactrocera dorsalis (Hendel),by integrating the sterile insect technique (SIT) with other monitoring and control methods in the mango-production areas in the Paktor District in the Ratchaburi province. The project includes mass-rearing and sterilization of OFF at the mass-rearing and sterilization facility of the Irradiation for Agricultural Development Institute, DOAE, located in the Pathumthani Province and field releases of sterile flies complemented by bait sprays and a monitoring network of methyl eugenol baited traps. The International Atomic Energy Agency has provided technical assistance since 1991 through a Technical Cooperation Project. The assistance has resulted in improved rearing and field operation activities. In the years 1999 and 2000, weekly ground shipments of 5 10 million sterile pupae were transported from the production facility in Pathumthani to Paktor District for ground release in 1120 ha of small commercial mango orchards. Quality control tests of the released sterile flies were routinely conducted. A trapping network of 25 methyl eugenol traps (2.2 traps/km 2 ) was serviced weekly to monitor the distribution and abundance of the sterile flies released. Periodic fruit sampling was carried out to assess the impact of the control measures by determining the percentage fruit infestation. Infestation levels have been reduced from over 50% before the application of the integrated SIT, to an average of less than 4% in the past seven years ( ) with a significant reduction to 1.3% in The mango growers in the area of the project have been exporting over 50% of their mango production to countries that do not require a fly-free certificate such as Canada, Hong Kong, Malaysia, Singapore, etc., but discriminate against pesticide residues and fruit quality. Small volumes of mango have also been exported to Japan but only after attaining compliance with a post-harvest treatment and a Federal Phytosanitary Certificate.The economic benefits of SIT for the participating mango growers have been substantial. Farmers claim that mango has become a profitable business since the use of SIT for control of the key pest (i.e. OFF) and that mango growers in the neighbouring areas are eager to join the SIT project. An economic analysis projected over 14 years indicates a benefit to cost ratio of 7.5 to 1 and a net benefit of US$7.5 million for the mango growers of Paktor. This project has reached a stage where it could be scaled up to a national level with proper support from the government and mango industry. Despite the fact that this project is one of few examples of the routine use of SIT for effective suppression of fruit flies, substantial improvements are needed in order to cost-effectively apply the SIT at a larger scale. The basic requirements for scaling up include: 1) strengthening of the management structure, 2) implementation of SIT on an area-wide basis for effective pest control and to allow economies of scale,3) scaling up the sterile fly rearing capacity to 300 million flies per week, 4) incorporating new and better technologies such as the aerial release of chilled adults, more environmentally friendly insecticide products for population suppression and use of female trapping systems, and 5) improving monitoring systems through the application of GPS/GIS for sterile fly release and operation of trapping networks. INTRODUCTION The oriental fruit fly (OFF), Bactrocera dorsalis (Hendel), is a major pest of fruits in Thailand causing annual losses to the fruit industry estimated in millions of dollars as a result of significant *To whom correspondence should be addressed. w.r.enkerlin@iaea.org yield reduction and market restrictions. Insecticide applications to control fruit flies are done on a calendar basis and are widespread. Concerns about environmental pollution, undesirable chemical residues and the preservation of biodiversity, demand new insecticide-independent strategies and technologies for combating fruit

2 224 Proceedings of the 6th International Fruit Fly Symposium flies. The sterile insect technique (SIT) is one such environmentally friendly technology. This technique has been highly successful in pest management programmes in various parts of the world for control and eradication of harmful insect pests, such as fruit flies, tsetse flies, screwworms and certain caterpillars (IAEA 1999). The Department of Agricultural Extension (DOAE) in cooperation with the Office of Atomic Energy for Peace (OAEP) has the mango-production areas of Ratchaburi Province since This pilot project in Ratchaburi has been assisted with technical cooperation from the International Atomic Energy Agency (IAEA) of the United Nations since The SIT technology, including field activities and mass-rearing, sterilization and release of flies has been transferred through IAEA expert missions, fellowships and scientific visits. In 1987 the government of Thailand decided to adapt some facilities of the Centre for Irradiation of the DOAE into an OFF mass-rearing and sterilization facility. Since that date the facility has been producing an average of 10 million sterile flies per week for the project. The IAEA Board of Governors recently approved an extension of the SIT Pilot Project for three more years ( ). The technology transfer has not been an easy task; however, after years of effort, it has paid good dividends to a small number of mango growers in the District of Paktor, in the Ratchaburi Province. According to the information provided by the DOAE and confirmed by one of the farmer associations in Paktor District, the OFF damage decreased from over 80% in 1987, before the implementation of the SIT project, to 30, 26, 21, 18, 17 and 9% in the following six years (i.e to 1993), respectively (Changjaroen et al. 1996; Sri-arunothai 1998). From 1994 to 2001 the damage has been reduced further to an average of less than 4%. The economic benefits of SIT for the mango growers of Paktor has been substantial. Farmers claim that mango has become a profitable business since the use of SIT for control of the key pest (i.e. OFF) and that other mango growers are eager to join the SIT project. The paper describes the project activities during the 1999 and 2000 season and presents an economic analysis of SIT use for suppression purposes in the pilot area. This assessment is unique in the sense that the economic returns of the SIT project in Paktor, which started in 1988, are estimated and compared against the economic returns of conventional control options and an improved SIT control option. MATERIALS AND METHODS Release area The release area is situated in Paktor District, Ratchaburi Province, southwestern Thailand. It is a lowland area surrounded by areas under cultivation of field crops. Releases were made over 1120 ha of mango and other fruit crops. Subtropical climatic conditions allow for a high diversity and continuity of fruit hosts,making isolation virtually impossible. Mass-rearing The mass-rearing and sterilization facility of the Agricultural Development Institute (IAD), DOAE, located in Pathumthani Province has recently been upgraded to a production capacity of 30 million sterile OFF pupae per week. Current production is 10 million per week. Adult flies are housed in sixty rectangular cages constructed of an aluminum sheet or plywood and covered with an insect screen (Vargas 1984), each cage containing approximately adults. The temperature of the adult rearing room is maintained at 26 ± 2 C and relative humidity at 65 70%. The adult flies are fed an artificial diet consisting of a 4/1 volumetric mixture of granulated sugar and ICN yeast hydrolysate (ICN Pharmaceutical, Cleveland, Ohio). Water is supplied to the cages by a PVC tube with a filter paper. Females start to produce eggs 10 days after emergence. Adults of the breeding colony are kept for 28 days producing eggs, then the cages are replaced with newly emerged massreared adults. Female flies lay eggs during the day into perforated bottles, which are removed from the cages for egg collection (Tanaka,1965; Steiner & Mitchell 1966; Tanaka et al. 1970; Vargas 1989). The eggs collected are directly seeded into a wheat bran-based diet (Tanaka et al. 1969). The composition of the larval diet is presented in Table 1 and is expressed in percentage of the total weight. The larval diet is prepared using a 250-l capacity industrial mixer. Approximately eggs are seeded on the fibreglass tray (Model Fiber Glass ) containing 6 l diet per tray. The trays are placed in a trolley and transferred to the initiation room with a temperature of 27 ± 2 C and 90% RH. On the sixth day, after the transfer into the initiation room, the diet trays are transferred to a lower temperature room at 22 ± 2 C and held there until the larvae are fully developed. The mature larvae pop out of the diet and fall into a metal tray filled with sawdust. The larvae pupate in the dry substrate. The pupae are separated from the

3 Sutantawong et al.: SIT for control of oriental fruit fly in mango orchards in Thailand 225 Fig. 1. Sketch showing the oriental fruit fly release area in Paktor District, Ratchaburi Province. sawdust with a mechanical sifting device. The sifted pupae are placed into the pupal trays, held on racks and stored in the pupal storage room at 20 ± 1 or 27 ± 1 C. Quality control tests are conducted every time on fly ability and emergence, sex ratio, egg hatch, and pupae weight following the International Fruit Fly Quality Control Manual (Anon. 1998; Wornoayporn 1999). Sterile fly release Before irradiation, the pupae were marked with 2 g of blaze orange fluorescent dye powder (Day-Glo ) per litre of pupae) two days before emergence. The marked pupae were packed into 500-ml polyethylene bags, which were then closed with rubber bands to induce anoxia. The Table 1. Formulation of the diet used for oriental fruit fly at the Pathumthani mass-rearing facility (per 100 kg diet). Ingredient % (weight) Wheat bran 26.0 Granulated sugar 12.0 Brewer s yeast 3.6 Sodium benzoate 0.1 Nipagin (methyl-p-hydroxybenzonate) 0.1 HCl 0.2 Water 58 bags with pupae were packed into polystyrene containers and kept cool with ice packs. The pupae were sterilized with 90 Gy of gamma radiation from a 60 Co source before being shipped to Paktor District, Ratchaburi Province. Weekly shipments of approximately 5 10 million pupae of both sexes were transported by ground in a refrigerated truck and delivered directly to the SIT-treated area. Upon arrival at the release area, the bags with pupae were taken out of the container and pupae were placed in a wooden container ( cm), with pupae per container. Six containers were placed into a release hut. Twenty-two release sites were uniformly distributed in the release area (Fig. 1). A small sample of pupae was systematically taken for quality control testing. Weekly releases were carried out at a density of pupae per hectare. Monitoring of populations Monitoring was based on trapping techniques and on fruit surveillance. Twenty-five monitoring Steiner s traps baited with methyl eugenol and insecticide were placed throughout the release area (Fig. 1). All the traps were inspected weekly. The flies were removed from the trap, identified and recorded. Marked sterile flies in traps were separated from unmarked flies using a microscope with a UV light source. Examination of trapped flies consisted of identifying dye particles in the

4 226 Proceedings of the 6th International Fruit Fly Symposium Table 2. Description of the different control options for oriental fruit fly in this study. Option Description Damage level (%) Conventional control (low input) Conventional control (high input) SIT suppression on an orchard-by-orchard basis (status quo) SIT suppression areawide (improved option) Minimum orchard management is carried out by farmers. Irregular pest control is done. Moderate orchard management is carried out including pruning, orchard sanitation and a conventional pest control programme at orchard level. OFF control includes from 7 10 calendar insecticide cover sprays per season. Moderate orchard management is carried out including pruning, orchard sanitation, minimum level of population monitoring, 1 2 insecticide sprays against OFF and permanent ground releases of sterile flies at orchard level. Intensive orchard management is carried out including pruning, orchard sanitation, optimum level of population monitoring, permanent aerial releases of sterile flies in orchards and marginal areas. A government centralized management structure is in place where farmers actively participate in monitoring and control activities in the orchards and the government takes responsibility for activities in the marginal areas <1 body sutures, on the cuticle and on the ptilinum in the head. Fruit surveillance was done throughout the release area. A total of 500 mangos in 1999 and 1700 in 2000 were collected and maintained in plastic boxes to observe the emergence of OFF adults. Economic assessment Methodology. Four control options were analysed: 1) conventional control (low input),2) conventional control (high input), 3) SIT suppression on an orchard-by-orchard basis (status quo) and 4) SIT suppression area-wide (improved option). A brief description of the four control options is presented in Table 2. For each option costs, benefits and economic indices were estimated using basic information on current control practices, pest damage, production volumes and values, market shares, farm gate prices in domestic and export markets and macroeconomic indicators (i.e. inflation rates, interest rates). The information was provided by DOAE officials from the Ratchaburi Province and by one of the mango associations in the Paktor District where the SIT pilot project has been carried out since For the control options analysed the flow of costs and benefits was estimated for a time horizon of 14 years, which is the amount of time that has passed since the project started back in 1988.The total costs and benefits across 14 years were discounted using a discount rate of 8% based on Thailand s current inflation and interest rates. Cost estimates. Three main sources of direct costs were identified as follows:1) production loss due to direct damage from pest, 2) costs of conventional, current and improved control programmes and 3) market losses due to lack of comparative advantages to access the export market. For each control option the cost due to direct damage from pest was computed by multiplying the yield loss in tonnes per hectare by the farm gate price. A price differential was used based on the current mango prices for domestic market and for export markets not discriminating against fruit flies such as the ones currently importing substantial amounts of mango from the pilot SIT project area (Singapore, Hong Kong, Malaysia, Canada, etc.). The total amount of mango lost due to direct damage was multiplied by 0.4 (40%) and by the average price for domestic market (US$0.18/kg) to compute the value of the production lost that would have been sold in the domestic market. The same procedure was followed for the share of the production lost that would have been sold in the export market (60%). So in this case the amount lost was multiplied by 0.6 (60%) and by the average price for the export market (US$0.49/kg). Both figures were added to estimate the total value of the mango loss due to direct damage by the OFF. The total cost per year for the conventional control programmes included costs of insecticide treat-

5 Sutantawong et al.: SIT for control of oriental fruit fly in mango orchards in Thailand 227 Table 3. Revenues obtained from the use of SIT against the oriental fruit fly in mango orchards (on an orchard-by-orchard basis) in the Paktor District in Thailand. Year Damage Maximum yield Yield after damage Total area Price* Value (%) (tons/ha) (tons) (ha) (US$/ton) (US$ million) Total 15.6 *Weighted average for domestic and export prices based on 40% sales in domestic market and 60% sales in export market. ment against OFF (1 2 for the low input and 7 10 for the high input per season), orchard sanitation and pruning. For the status quo (SIT used on an orchard-by-orchard basis) and improved option (SIT used on an areawide basis) the costs included costs of insecticide treatment against OFF (1 2 per season), orchard sanitation, pruning, monitoring with methyl eugenol traps, fruit sampling and sterile fly release. In the case of the status quo only limited trapping and fruit sampling is carried out and sterile flies are ground released in orchards. In the case of the improved option optimum trapping, fruit sampling and aerial release of sterile flies on an areawide basis (inside and outside the orchard) was assumed. Market loss was computed by assuming that the conventional control options do not have access to the more high-value export market compared to the status quo and the improved option. There is a substantial loss in potential revenues from not being able to export the fruit. For example, the mango growers in the area where the SIT is being used are exporting 60% of the production. This generates an annual gross revenue of US$1.2 million compared to US$0.6 million if all the production was sold in the domestic market. No information on indirect costs (i.e. environmental impact) including cost of insecticide poisoning treatment for field workers, secondary pest outbreaks due to natural enemy mortality and reduction in honey production and pollination due to honey bee mortality was included in the assessment. Benefit estimates. For the conventional control options (low and high input) the only source of benefits is the revenues obtained from the mango produced and sold in the domestic market as a result of control actions against the OFF. In the case of the low-input control only 20% of the mango potential production is actually produced (i.e. a loss of 80%) and 70% in the case of the highinput control option (i.e. a loss of 30%). This source of benefit also applies to the status quo and the improved control options. In the case of the status quo option substantial revenues are obtained from reducing OFF damage to less than an average 4% and to less than 1% for the improved option. In the case of the status quo SIT control option (i.e. only used in orchards) which has been implemented in Thailand since 1988 it is clear that OFF damage was gradually reduced;however,it took six years before the damage was reduced from the initial 80% to less than an average 4% per year. The gradual reduction in damage levels and consequent increase in gross revenues is clearly shown in Table 3. For the improved control option (i.e. area-wide SIT), it was assumed that the project starts in year 2001 and that it would take three years to reduce the current 4% damage levels to less than 1%. It is also assumed that once the damage levels have been reduced below 1% (in year 5) and insecticide sprays against OFF have been fully eliminated the price increases from a weighted average of US$370/ton to US$540/ton (i.e. a projected arbitrary increase of 45% in price)

6 228 Proceedings of the 6th International Fruit Fly Symposium Table 4. Projected revenues from the use of SIT against the oriental fruit fly in mango orchards (on an area-wide basis) in the Paktor District in Thailand. Year Damage Maximum yield Yield after damage Total area Price* Value (%) (tons/ha) (tons) (ha) (US$/ton) (US$ million) Total 22.0 *Weighted average for domestic and export prices based on 40% sales in domestic market and 60% sales in export market. In this case from year 9 (1995) due to a more effective application of the SIT which results in the complete elimination of insecticide use and assuming that the mango growers have managed to effectively negotiate a premium for the better quality fruit, the weighted average price increases from US$370/ton to US$540/ton. due to a premium paid by the clients. Table 4 presents the projected gross revenues for this control option. Apart from this benefit (i.e. revenues from increase in mango yields due to effective OFF control) the status quo and improved options also benefit from savings in insecticide use from the conventional control options and from being able to sell the fruit at a better price in the export markets. These more environmentally friendly control options also benefit from savings in environmental cost. Unfortunately no information was available to estimate the value of this important indirect benefit. The gross revenues (in US dollars million) were estimated for each control option by adding the different sources of benefits. Having estimated the costs and benefits (gross revenues) for each control option the economic returns were computed. Economic indices. To measure the economic feasibility of the four control options analysed three economic indices were calculated: 1) the benefit to cost ratio, 2) net benefits (net present value) and 3) pay-back period. Other important indices such as the internal rate of return (IRR) and the return on equity (N/K) were not calculated since for all control options analysed the economic returns are positive from year 1. The benefit to cost ratio is computed by dividing the gross revenues by the total cost. A value smaller than 1 indicates that the control option is not economically viable. A value equal to 1 indicates that the control option breaks even in the projected time frame and a value greater than 1 indicates that the control option is economically viable and that for each monetary unit invested a profit margin is obtained. The net benefit is computed by subtracting the total costs from the gross revenues. A value smaller than 0 indicates that the control option is not economically viable. A value equal to zero indicates that the control option breaks even and a value greater than zero indicates that the option is viable and that a profit margin is being produced. The pay-back period is the time required to pay for the initial investment of the control option. For the investment to be economically feasible the pay-back period has to be obtained before the time frame of the project has expired (Enkerlin 2001). RESULTS AND DISCUSSION Mass-rearing In 1999 and 2000,112.5 and 129 tons of larval diet was used yielding c. 959 and 872 millions of pupae, respectively, resulting in an average production of 18 million pupae per week in 1999 and 16.7 million pupae per week in The average yield of pupae and percentage pupal recovery in 2000 is lower than that in The high variability in pupal recovery is a result of not being able to maintain stable conditions throughout the rearing

7 Sutantawong et al.: SIT for control of oriental fruit fly in mango orchards in Thailand 229 Table 5. Average parameters of quality control tests for the oriental fruit fly at the Pathumthani production facility in Year Egg hatch Pupal weight Pupal recovery Adult eclosion (%) (mg) (%) (%) ± ± ± ± ± ± ± 1.9 Fig. 2. Average number (millions) of sterilized oriental fruit fly pupae released and estimated number of flies emerged during ( pupae, adults 1999; pupae, adults 2000). process. Table 5 show the average of the results of oriental fruit fly quality control test in 1999 and 2000, respectively. Release Figure 2 presents the number of sterilized pupae released during , and number of adults that emerged. Figure 3 show adult eclosion and flight ability of flies after irradiation at the Pathumthani production facility and transportation to the Paktor District during 1999 and Adult eclosion and flight ability in the shipments arriving at Paktor was variable between shipments. The data from Pathumthani suggested that the shipment and handling contributed most to decrease in adult eclosion and flight ability Monitoring The ratio between released and native males was calculated from the captured flies from the traps. Fig. 3. Adult eclosion and flight ability of oriental fruit fly after irradiation at the Pathumthani production facility and transportation to the Paktor District during 1999 and 2000 ( Pathumthani, Paktor 1999; Pathumthani, Paktor 2000).

8 230 Proceedings of the 6th International Fruit Fly Symposium Table 6. The monthly ratio of oriental fruit fly sterile males to wild males captured in methyl eugenol traps in the Paktor District in 1999 and Year Ratio of sterile males to wild males J F M A M J J A S O N D /1 5.3/1 12.8/1 8.1/1 4.4/1 1.2/1 2.0/1 1.4/1 3.6/1 6.8/1 9.5/1 31.8/ /1 9.6/1 2.2/1 1.1/1 1.1/1 1.6/1 3.0/1 3.5/1 6.8/1 10.0/1 45.2/ /1 The ratio of sterile males to wild males during the critical months (September to March) was acceptable considering that the aim of the programme is population suppression and not eradication. The sterile to wild ratios were more favourable in 2000 compared to 1999 (Table 6). This resulted in a 5.9 and 1.3% fruit damage for 1999 and 2000 compared to over 50% before the use of SIT. In total, 559 mangos were checked in the SIT area at Paktor from March May Of these, 33 were found with live OFF maggots. During March May 2000, 1727 mangos were inspected for OFF damage. Of these, 23 were found with live OFF maggots. The infestation rates in 1999 and 2000 are presented in Table 7. Economic assessment Conventional control (low input). Mango production in Thailand under a low-input production scheme with minimum pest control activities is common. As the economic figures indicate this is basically a subsistence mango-production system where farmers operate at low costs and obtain a very low profit margin. If the mango orchards in Ratchaburi where the SIT is currently being applied would go back to a low-input production scheme, in 14 years (i.e. time frame of the analysis), the total production cost would be US$0.79 million (US $78/ha/year), the gross revenues would be US$0.98 million (US$96/ha/year), the benefit to cost ratio would be 1.2 and the net benefits US$0.12 million equivalent to US$11.8/ha/year (Table 8). The average farmer in Thailand has Table 7. Percentage of mangos infested by the oriental fruit fly after releasing sterile flies in the Paktor District in 1999 and Year No. of sampled % Infested fruits fruits around 2 ha of mango. So the total income for an average farmer would be of only US$192/year, which is well below the annual minimum wage in Thailand. Conventional control (high input). Mango cultivation under a high-input production scheme is done only on 4% ( ha) of the total mango planted area in Thailand. Pest control, including the OFF, is carried out through repeated insecticide treatments in the form of calendar cover sprays during the crops fruiting season. In the case of OFF, 7 10 insecticide treatments are done to protect the crop throughout the season. This is an expensive and ineffective control method that does not provide farmers with any comparative market advantage. According to a group of farmers in Thailand, mango growers that use this pest control scheme lose 30% of the crop despite the heavy insecticide applications and have no chance to export their fruit because of insecticide residues and low quality of the fruit. If the farmers currently using the SIT to protect their orchards were forced to shift to a conventional high-input pest control scheme based on Table 8. Economic indices for the different control options for oriental fruit fly in this study. Option B/C ratio Net benefits Gross revenues Cost NPV Pay-back NPV (US$ million) (US$ million) (US$ million) Conventional control (low input) NA Conventional control (high input) NA SIT suppression: orchard-by-orchard NA SIT suppression: area-wide

9 Sutantawong et al.: SIT for control of oriental fruit fly in mango orchards in Thailand would be US$2.6 million (US$256/ha/year), the annual gross revenues US$5.9 million (US$580/ha/year), the benefit to cost ratio 2.3 and the net benefits US$1.9 million equivalent to US$187 per hectare per year. These economic indices are favourable compared to the low-input conventional control method described above. However, if compared against the status quo (i.e. orchard-by-orchard SIT) and against the improved option (i.e. area-wide SIT) the economic indices are much less favourable, apart from the fact that this option would imply the need for intensive use of insecticides which would have adverse impact on the environment and on food quality and most likely not be sustainable in the long term (Table 8). Orchard-by-orchard SIT (status quo). Only a very small fraction of the total farmers producing mango in Thailand are currently benefiting from controlling the OFF through the SIT. The total mango area under SIT suppression is 1120 ha (7000 Rai) which is only 0.2% of the total cultivated area in Thailand. The pilot SIT project in the Ratchaburi Province started in the year It took six years before the OFF populations were effectively controlled. For example, in six years ( ), in the mango-production area in the Paktor District in the Ratchaburi Province, damage was reduced from 80% before the project started to 8.5%. In the following seven years ( ) the average damage was reduced to less than 4%. The current pilot project in Paktor can be considered an economic success for the mango growers despite the fact that the SIT is not fully applied following the recommended technical procedures. For example, field operations are not carried out following the area-wide approach, thus trapping and sterile fly release are done only at the orchards, sterile flies are release by ground and in the pupal stage instead of releasing by air and using the chilled adult release method, the sterile fly densities are 10 times greater than the recommended rate ( sterile flies/ha instead of 1000/ha), the trapping network does not include female traps and the densities are below the recommended levels and no systematic fruit sampling is carried out. This non-optimal use of the SIT makes the technology expensive and reduces its effectiveness. However, even when the SIT technology is not being properly used,off damage has dropped to less than an average of 4% in the past seven years and farmers, by using an environmentally friendly technology, have found better prices for their mangos in the export market. For the orchard-by-orchard SIT used in the mango-production areas of Paktor the economic analysis projected over 14 years indicates a benefit to cost ratio of 7.5 to 1 and a net benefit of US$7.5 million. This is equivalent to an annual net benefit of US$738/ha, which is almost four times greater than the net benefits obtained through the highinput conventional control options (Table 8). Area-wide SIT (improved option). The proper use of the SIT for OFF control in the mango-production areas of Paktor could further improve profits of mango production as the economic analysis shows. By using an area-wide approach the sterile fly density currently used in the orchards of sterile pupae per hectare (c adult flies/ha) could be reduced 8 times (to 1,000 sterile flies/ha). Part of the remaining sterile flies (another 1000 sterile flies/ha) would be released in the marginal areas around the orchards to create an OFF buffer zone. Still around 6000 flies per hectare would be available to expand the SIT use to other mangoproduction areas in Paktor or elsewhere. Owing to the more effective use of the sterile flies the cost of an area-wide SIT project would be practically the same compared to the status quo. The cost of the current project has been estimated to be around 1.8 million dollars in 14 years compared to US $1.7 million for an area-wide approach. The effective use of SIT would reduce OFF damage to less than 1% greatly improving the gross revenues compared to the status quo. An additional benefit of the area-wide approach would be the complete elimination of insecticide use (under the status quo two insecticide treatments are applied per season) and, apart from the savings from insecticide use, the mangos could be sold at a higher price through a premium paid by the clients for low insecticide residues and high quality fruit. According to the economic analysis, for a 14-year time frame,the benefits to cost ratio for this control option is 10.5 compared to 7.5 under the status quo, the net benefit US$11.3 million and the initial investment would be paid in the first year (Table 8). The pay-back period in year 1 is possible basically because the major capital investment, which is the fruit fly factory, is already in place and producing enough flies for the mango-production areas in the Paktor District and because the major benefit, which is reduction of the current 4% damage (average of the past seven years) to less than 1% and savings in insecticide treatments, would be obtained in the first year considering the more than 10-year experience in the use of SIT technology. Some capital will have to be invested in a packing and release centre. Equipment such as

10 232 Proceedings of the 6th International Fruit Fly Symposium vehicles,chilled adult release machine and GPS/GIS devices will have to be purchased, nevertheless, net benefits are positive from year 1 and increase gradually as the level of damage is reduced,insecticide sprays are eliminated and the mango is sold at a better price in the export market. CONCLUSIONS The current SIT pilot project in the mango orchards in the Paktor District has had a positive economic impact for the farmers despite the fact that SIT has mainly been applied at orchard level rather than on an area-wide basis. Mango yields have substantially increased, insecticide spraying has been reduced by five fold and the export market to countries not discriminating against OFF has been opened due to the improved quality of the fruit. The profitability of the pilot project can further improve if the project shifts from an orchard-byorchard management approach to an area-wide approach and if the techniques used are updated and optimized. The positive economic impact of SIT technology on the mango producers of Paktor should be used to promote SIT at a national level. The pilot project in Paktor should be converted into a model project and the SIT technology transferred to the rest of the mango-production areas in Ratchaburi and rest of Thailand. The technology transfer should be done through a Government National SIT Suppression Programme with active participation of the mango industry. ACKNOWLEDGEMENTS The use of the sterile insect technique (SIT) for control of the oriental fruit fly, Bactrocera dorsalis (Hendel) in mango orchards in Ratchaburi Province, Thailand, would not have been possible without the immense support of numerous organizations and individuals. Although we cannot list all cooperators as authors, the authors wish to gratefully acknowledge the following organizations: International Atomic Energy Agency (IAEA), Office of Atomic Energy for Peace (OAEP), Department of Agricultural Extension (DOAE), Office of Agricultural Extension Ratchaburi Province, Office of Agricultural Extension Pichit Province, Office of Agricultural Extension Western Region. We are also grateful to Mr Pramoed Raksarat, Mr Prarop Changjaroen, Dr Cherdchai Banditsingha, and Ms Renu Dokmaihom, for their commitment to and strong support of the project. Additionally, the technical support beyond what was expected from the Insect Pest Control Section staff of the FAO/IAEA Joint Division, especially to Dr Jorge Hendrichs and all recruited experts is much appreciated. We thank Mr Naicheng Xu, Project Officer, Technical Cooperation Department, for his effective support. Finally, the programme could not have gone forward without the cooperation and enthusiasm of the many growers and SIT programme staff who actively embraced the concept and who have supported the activities of the many duties involved. REFERENCES ANON FAO/IAEA/USDA. A Manual of Quality Control for Fruit Flies. IAEA Vienna, Austria. CHANGJAROEN, P., DOKMAIHOM, R., FUNGVITTAYA, P., CHOORNPHURAT, C. & STAFF Fruit fly control by the sterile insect technique (abstract). In: 6th Nuclear Science and Technology Conference, Bangkok, Thailand. 43. Ministry of Science Technology and Environment, Bangkok, Thailand.. ENKERLIN, W.R An economic assessment for Oriental fruit fly control using the Sterile Insect Technique (SIT) in Thailand: a case study for the mango production areas of Paktor District. IAEA, Technical Cooperation Project THA5046. Vienna, Austria. IAEA Entomology. In: The International Atomic Energy Agency s Laboratories Seibersdorf IAEA, Vienna, Austria. SRI-ARUNOTHAI, S Area wide control of fruit fly by the sterile insect technique. In: 7th Nuclear Science and Technology Conference, Bangkok, Thailand Ministry of Science Technology and Environment, Bangkok, Thailand. [In Thai.] STEINER, L.F. & MITCHELL, S Tephritid fruit flies. In: Smith, C.N. (Ed.) Insect Colonization and Mass Production Academic Press, New York. TANAKA, N., STEINER, L.F., OHINATA, K. & OKAMOTO, R Low-cost larval rearing medium for mass production of Oriental and Mediterranean fruit flies. Journal of Economic Entomology 62: TANAKA, N Artificial egging receptacles for the species of tephritid flies. Journal of Economic Entomology 58: TANAKA, N., OKAMOTO, R. & CHAMBERS, D.L Methods of mass rearing the Mediterranean fruit fly currently used by the U.S. Department of Agriculture: In: Proceedings of a Panel on Sterile-male Technique for Control of Fruit Flies IAEA, Vienna. WORNOAYPORN, V Report on duty travel to Thailand, 26 March 12 April, IAEA, Vienna, Austria. VARGAS, R.I Alternative egg collection system for mass production of Mediterranean fruit fly (Diptera: Tephritidae). Journal of Economic Entomology 77: VARGAS, R Mass production of tephritid fruit flies. In: Robinson, A.S. & Hooper, G. (Eds) World Crop Pests, 3B; Fruit Flies Their Biology, Natural Enemies and Control Elsevier, Amsterdam.