Fruit fly alert: Vigilant scout does the right thing
Figure 1: Fruit fly traps were
placed in the block of
mandarins
Of all the biosecurity threats facing New Zealand, the public profile of the fruit fly is up there alongside foot and mouth disease. Reflecting the scale of damage these pests could cause if they ever became established, a nationwide fruit fly surveillance trapping programme is undertaken annually by MAF Biosecurity New Zealand (MAFBNZ) to detect any incursions. The vigilance of people working in horticulture is another important component of the surveillance toolbox – as illustrated on a Gisborne citrus orchard recently.
Fruit and vegetable growers, packers and distributors – in fact most people who deal with fruit fly host plants – are educated to keep a constant look out for signs of the pest. It is not surprising, then, that someone might find something to trigger a fruit fly investigation. This is what happened in June this year, when a citrus industry employee reported seeing a suspect adult fruit fly.
Suspect takes flight
The employee – a pest and disease scout working in a Gisborne mandarin orchard – spotted an insect on a fruit that she had never seen before. The suspect insect flew away so, with no specimen available for identification, the scout followed her training by consulting integrated pest management (IPM) manuals and other literature to try to identify what she had seen. Queensland fruit fly (Bactrocera tryoni), a serious pest, seemed the most likely match.
MAF was notified through the pest and disease hotline and an investigation was immediately launched. This involved staff of MAFBNZ's Investigation and Diagnostic Centre (Plants and Environment). An incursion investigator arrived at the orchard the following day to oversee placement of fruit fly traps (Figure 1) and carry out interviews.
Harvesting had just begun in the block of mandarins (Figure 2), with some fruit already waiting at a packhouse for export. This fruit was isolated and put on hold while investigations continued.
Given the time of year, weather conditions, and the biology of Queensland fruit fly, it was very unlikely there were fruit fly on the orchard. It was considered prudent to investigate the risk further, however. So as not to cause undue concern in the wider citrus export industry, this was done in a low-key way.
Figure 3: Images of adult fruit fly as they appear in the citrus
pest and disease manual, within a 'Biosecurity Risks'
section
No other evidence of fruit fly
No further evidence of fruit fly was found: no fruit fly adults were caught in traps, and no suspicious fruit damage found. The suspect fruit fly adult had been seen crawling out of a fruit rot lesion, immediately after the scout picked the fruit during routine sampling. There were no fruit fly eggs, larvae or damage typical of fruit fly on this fruit.
Other fruit showing the same type of rot lesions were collected from nearby and examined in the laboratory by IDC, Plant Health Environment Laboratory diagnostic staff. While no evidence of fruit fly was found on fruit with rot lesions, other insects, such as Phorid flies, were found. It is possible the scout had seen such an insect, rather than a fruit fly. The poor photo quality of the image in the IPM manual consulted (Figure 3) may also have contributed to initial suspicions that it was Queensland fruit fly.
Considering this and other information, and the negative results from the national fruit fly surveillance programme for the Gisborne region during the summer of 2006–2007, the risk that there had been a fruit fly incursion was very low. No further action was recommended.
Grower's cooperation acknowledged
IDC was thankful to the grower involved, who had shown the utmost cooperation during the investigation and had voluntarily directed harvested fruit to the local market rather than export during the three-week fruit fly trapping programme. Knowledge of the investigation was restricted to those with a 'need to know', with a 'heads-up' communication to industry leaders and the fruit packhouse/exporter involved. Although this investigation proved negative, the scout was congratulated for acting appropriately. Reports like these form the basis of general surveillance and are an important component of our surveillance system.
This investigation highlighted the importance of frontline industry staff in surveillance, of specimen collection, and of appropriately skilled diagnosticians for rapid identification of the suspect organism.
- Graham Burnip, Incursion Investigator (Plants and Environment), Investigation and Diagnostic Centre, MAF Biosecurity New Zealand, Lincoln, phone 03 943 3208, graham.burnip@maf.govt.nz
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Page last updated: 30 April 2008