Tongan export to NZ, a political decision [1]
Thursday, July 23, 2009 - 06:00. Updated on Monday, April 28, 2014 - 10:16.
Editor,
With great pleasure did I read about new attempts of NZ assistance to the Tonga economic development. I have been working at the Vaini Experimental Farm of the Research Division of the MAF Tonga, and here is my proposal as just one contribution to re-development.
An easy step would be the lifting of the ban on water melon exports to NZ in 1988.
There have been several scientific studies in Tonga that have shown the non-risk of fruit infestation by fruit flies, if area management and fruit quality control are properly implemented. Science can not further solve the problem, it is a matter of politics now to act.
Please find enclosed a short scientific review.
FRUIT FLIES
Retrived from: 'Tonga Islands Environment Reference Book' unpublished manuscript by D.-H. Stechmann, 2007
Fruit flies in Tonga
Six species of Bactrocera spp. (Dacinae) are occurring in Tonga, all primarily of quarantine importance (Waterhouse 1993, Drew & Romig 1997, Heimoana et al. 1997a, b, c, Tupou et al. 2001):
B. distincta: occuring in Fiji, Futuna, Niue, Samoa and Tonga (all island groups); 8 host plant species of non-export crops.
B. facialis: endemic to Tonga (Tongatapu, 'Eua, Ha'apai, Vava'u); 41 host plant species mostly from commercial fruit crops;
B. kirki: occurring in American Samoa, Samoa, Niue, Tonga (all island groups), French Polynesia, Wallis & Futuna; 16 host plant species mostly from commercial fruit crops;
B. obscura: no detailed studies, occurring in Niue, Rotuma, Samoa and Tonga (in the Niuas only); host
plants not known in Tonga;
B. passiflorae: occurring in Fiji, Niue, Tonga (in the Niuas only), Tuvalu and Wallis & Futuna; 12 host plant species mostly from native, non commercial fruit crops;
B. xanthodes: sibling species complex, needs taxonomic investigations (Allwood 1997); pest species occurring in Cook Islands, Fiji, Niue, American Samoa, Samoa and Tonga (all island groups); records from the Western Pacific (Nauru, Vanuatu) need taxonomic clarification; 8 host plant species mostly from commercial fruit crops.
A seventh species, B. psidii Froggatt, is recorded for Tonga by Hardy & Foote (1989-2004) from records of an early description as Dacus virgutus Coquillet, 1909, but B. psidii was not found during surveys ever since. Possibly the species is extinct in Tonga. It is recorded as endemic to New Caledonia by the SPC fruit fly project (Drew & Romig 1997).
The experimental testing of fruit fly crop host plants in Tonga (Heimoana et al. 1997a) has substantially contributed to identifying the true pest status, particularly of the major fruit fly pests B. facialis and B. xanthodes, with the potential of reducing the quarantine risks of exporting fruit crops from Tonga. It was confirmed that watermelons and cucumbers (e.g. Squash cucurbits) are non-hosts of the two fruit fly species B. facialis and B. xanthodes (Stechmann et al. 1988). Thus the ban on water melon exports from Tonga to New Zealand is simply related to the lack of quality control of the exported commodity and has no general biological justification. Methods of controlling fruit flies are fully available, yet implementation would be a major effort.
These include at the present stage of experimentation the consideration of the following components:
(a) non-host status of the commodity, (b) area freedom, (c) trapping surveys, (d) field control using protein bait sprays (Heimoana et al. 1997 a, b, c). Also, classical biological control would be a means of reducing the pest status of some of the species, see Mitchell (1984) with the success story from Hawai'i, and Waterhouse (1993) with an analysis of the biocontrol prospects for the Pacific. The implementation, however, should be on top of the plant protection agenda due to the great potential of exporting valuable fruit and vegetable crops off-season from Tonga to Japan and New Zealand, see
McLeod (2005).
With kind regards
Dirk Stechmann
d [dot] stechmann [at] web [dot] de