Bactrocera (Tetradacus) minax (Enderlein) is a serious pest of mandarins in the Kingdom of Bhutan. The adult flies oviposit in the developing fruit resulting in significant drop of fruit before harvest. Fruit loss due to fruit fly infestation as been estimated to range from 20-80% in affected orchards. Development of an integrated pest management (IPM) programme in mandarin orchards is a priority of the National Plant Protection Centre (NPPC), Simtokha, Bhutan. A collaborative project between the NPPC and Griffith University, Australia, was established in January 1999 to develop improved methods of fruit fly control. Funding is being provided by the Royal Government of Bhutan and the Australian Centre for International Agricultural Research (ACIAR). The principal role of the Australian scientists, under the leadership of Prof. Richard Drew, is to provide expertise in fruit fly research.

The first year of the project was spent in making personal and professional contact between the groups associated with the project. This involved a visit by Mr N.K. Pradhan and Mr. C. Dorji to the fruit fly laboratory at Griffith University, Brisbane, Australia, and a visit by Prof R. Drew and Mrs M. Romig to the NPPC at Simtokha, Bhutan. These visits involved trips to relevant field sites, formal discussions and some preliminary laboratory work. Plans were also made for the beginning of field work in 2000.

The remainder of this document covers work that has been initiated in April 2000 during a visit by Prof. Richard Drew and Drs Tony Clarke and Brian Fletcher. Drew and Clarke are both based at Griffith University, while Dr Fletcher Fletcher has recently retired from the CSIRO Division of Entomology, where for some thirty years he was Australia's foremost expert on the ecology of tropical fruit flies.

The Chinese Citrus Fruit Fly, Bactrocera (Tetradacus) minax (Enderlein), is a serious pest of mandarins in the Kingdom of Bhutan. A collaborative project between the National Plant Protection Centre (NPPC), Bhutan and Griffith University, Australia was established in 1999 to develop effective, IPM compatible, methods for controlling B. minax in mandarins. Funding is being provided by the Royal Government of Bhutan and the Australian Centre for International Agricultural Research (ACIAR). The principal role of the Australian scientists involved in the project, under the leadership of Prof. Richard Drew, is to provide expertise in the areas of fruit fly research necessary to develop effective control procedures for B. minax in mandarin orchards.

The research phase of the project was initiated in April 2000 during a visit to Bhutan by Prof. Richard Drew, Dr. Tony Clarke and Dr. Brian Fletcher. In collaboration with Mr N.K. Pradhan (National Director, NPPC) and Mr C. Dorji (Chief Entomologist, NPPC) 2 sites were chosen for the planned field studies and a number of experiments to provide data on the ecology and behaviour of the flies were commenced. Dr Fletcher made a second visit to Bhutan from 13th - 29th November 2000. The main objectives of this visit were:
To assess the results collected to date
Help set up some experiments to determine the exit period of larvae from fallen fruit and factors determining the duration of the pupal period.
Evaluate priorities and start planning for the field work to be carried out during the 2001 season.

These objectives are addressed in the report

The experimental work, to date, has indicated the following:

Flies begin to emerge from puparia in mid to late April.
Dissection studies showed that some flies attain sexual maturity by the first week of June and can oviposit in mandarines from this time.
The results from the fruit bagging experiment concurred with the dissection data and indicated that oviposition occurred from early June to late July.
The egg hatch period has not been determined. This should be done as it may have an influence on the application of some proposed control measures.
Response to protein is strong during the period mid-May to late-June. By late-June, most flies are probably sexually mature.
Orange and yellow/green spheres are the most attractive visual cues. However, the numbers attracted may not be large enough to reduce fruit infestation rates. This could be tested in a field trial.
The pupal emergence experiments should be repeated from late-2002 to mid-2003.
During 2002, the following experimental program has been suggested:
(a) Test the efficacy of one or two dimethoate cover sprays. Possibly, only one application in the second week of June would be adequate.
(b) Conduct protein bait trials at Tsirang to evaluate the Australian Mauri Pinnacle protein and the Indian protein. These trials will include weekly treatments during the period from the beginning of June to end of July, as determined by the biological studies noted above.
(c) Assess the influence of farmer management practices on larval/pupae survival in the soil to see in some enhancement of physical pest control can be obtained.
(d) Experiments should be conducted to determine the time of egg hatch, larval departure from the fruit and pupal emergence.
The Bhutanese project staff have suggested that we should hold a 2-day Seminar in October 2002 to study all of the project results. This will be a valuable program and should provide information for planning field control strategies for farmers and a guide as to whether additional work is needed to improve these strategies.

With the approval of ACIAR, the project was put on hold for the year 2003. This was due to the rapid development of a severe citrus dieback problem in Bhutan which took all of their personnel and other resources. The project will resume in April 2004 with the onset of the new mandarin fruiting season.

With the approval of ACIAR, the project was put on hold for the year 2003. This was due to the rapid development of a severe citrus dieback problem in Bhutan which took all of their personnel and other resources. The project will resume in April 2004 with the onset of the new mandarin fruiting season.

Project progress in 2004
Two Griffith University fruit fly centre staff (Professor Drew and Meredith Romig) travelled to Bhutan in April 2005. During that visit, project field work was designed and implemented. Some of these field experiments were repeats of earlier work in 2002 where weather damage to field equipment prevented the collection of complete results.
Experiment 1 - Branch Bagging Experiment to determine oviposition period of Bactrocera minax
One hundred calico bags (1.5m x 1m) were sewn at the Griffith University fruit fly centre and taken to Bhutan in April 2005. These were used to enclose fruiting branches on mandarin trees at Rimchu. The branches were selected randomly and enclosed well before the fruit fly oviposition began. Every two weeks, until September 2004, bags were folded back on two branches in order to expose the fruit to fruit flies for oviposition. Exposure period was also 2 weeks, after which the branches were enclosed again with the bags. In October 2004, all branches were exposed and the fruit examined for infestation assessment.
Mr Chencho Dorji, the Bhutanese entomologist working on the project, has advised that a reliable data set was obtained on the oviposition period for this particular fruit fly species.
Experiment 2 - To measure the post-winter fly emergence period from pupae in the soil
At Rimchu, 12 emergence traps were placed in the field over larval infested mandarins. The pupae, in the soil, beneath the mandarins, would remain until post-winter emergence about April 2005. Data from this experiment will be collected and collated during April-May 2005.
Both experiments have been designed to provide valuable field data on the fruit fly life cycle that will be used to design field control trials to be conducted later in 2005.