The onion maggot (Delia antiqua) is the larvae stage of the onion maggot fly which can cause severe damage to onions but can also feed on other Alliums including shallots, leeks, garlic and chives. The adult onion maggot is a fly that is about half the size of a house fly, has a body that is grey in colour and has reddish eyes (Figure 2).
The onion maggot fly overwinters as a pupae in the top 15 cm of soil. In the early spring, adult flies emerge and the females lay small, white eggs ~2–10 cm below the soil line around the base of the plant. Once the eggs hatch, the larvae start feeding off susceptible Allium species. Small plants are most susceptible, and in onion, one maggot can kill up to 20 plants. Cool, wet weather favours development and without control, D. antiqua can reduce plant stands by over 50% if crops are not protected. Even if the plant is not killed, wounds caused by the larvae can cause secondary rots in storage.
Onion maggot management relies heavily on seed treatments, or on group 1B organophosphates, specifically chlorpyrifos insecticides which have been identified as a major surface water contaminant in some vegetable growing areas. The prospect of insecticide resistance and potential restrictions of use illustrate the importance of alternative management strategies for this insect. Sterile Insect Technology (SIT) in Quebec has proven to eliminate the application of soil and foliar chlorpyrifos insecticides in most fields while maintaining onion yields comparable to pesticide-based programs.
The idea is that by releasing sterile male onion maggot flies on a weekly basis, these male flies will mate with the wild, fertile females and the eggs that they lay will not be fertile. These eggs would not hatch into larvae, there would be no larvae to cause damage to the onion, and the population of flies would decrease over time.
This strategy has proven to be successful in Quebec, and acreage using SIT has grown from 346 acres in 2011 to 1680 acres in 2017. Work in Quebec has shown that the release rates of sterile flies could be decreased by up to 90% within 5 years of repeated use due to the reduction of wild populations while also decreasing the cost of the sterile fly program itself.
An AAFC project to demonstrate the use of sterile fly release technology for onion maggot management in Ontario was conducted in 2018 in collaboration with Phytodata Inc. and OMAFRA. The trial was set up in two fields of onion sets approximately 4.3 km apart with no other major onion fields within a 20 km radius. Flies were sterilized and released according to the protocol developed by Phytodata in the ‘release’ field while no flies were released in the ‘control’ field. Sticky cards were used weekly to monitor natural onion maggot populations as well as the displacement of sterile flies throughout the growing season. Sterile flies were differentiated on sticky cards by their colour as these flies were dyed pink before they were released.
Sticky card counts throughout the season indicate that the control field had a higher fertile fly pressure than the release field from June 13 until harvest. An average of 2.2 flies/trap/week were counted per trap in the release field compared to 5.4 flies/trap/week in the control (Figure 3). No pink flies were found on any of the sticky cards at the control field. Sticky cards were compromised by a weather event on August 22nd and therefore card counts were not quantified between August 15th and August 28th.
While this trial showed a population reduction of over 50% of fertile onion maggot flies at the release field within a single year, it is unknown whether the wild onion maggot population was equal between the two sites. A continuation of this program would most likely reduce the need of chemical control options for onion maggot fly in the area if continued. If you are interested in applying this management strategy on your farm, please contact Anne-Marie Fortier at afortier@phytodata.ca.
FULL REPORT
FIELD DEMONSTRATION OF THE STERILE FLY RELEASE TECHNOLOGY FOR ONION MAGGOT MANAGEMENT IN ONION SET PRODUCTION IN ONTARIO
NAME AND AGENCY:
CRANMER TJ1, FORTIER AM2, MAKELA K3, and GAGNON C3.
1Ontario Ministry of Agriculture, Food and Rural Affairs, Guelph, ON
2Consortium PRISME, Phytodata Inc, Sherrington, QC
3Agriculture and Agri-Food Canada, Ottawa, ON
MATERIALS: Sterilized/irradiated Delia antiqua pupae.
METHODS: Two fields of onion sets approximately 4.3 km apart were sown in Granby sandy loam near Exeter, Ontario in the spring of 2018. Both fields were seeded at a high density of ~20 million seeds / ha (~8 million seeds / ac) with no soil application of chlorpyrifos. The release field was approximately 7.4 ha (18.3 ac) in size and was sown on 10 May. The control field was approximately 3.7 ha (9.3 ac) in size and was seeded one week after the release field approximately 4.3 km away (Figure 1). There were no other major onion fields within a 20 km radius from either the control or release field. The field used for onion sets the previous year (2017), was approximately 2.8 km and 2.9 km away from the control and release fields respectively. Onion flies were produced by Phytodata, and then sterilized and released according to the protocol developed by Phytodata, using the Sterile Insect Technology (SIT). The Delia antiqua pupae were irradiated by Nordion and then shipped to Guelph, ON, and kept alive until release following protocols developed by Phytodata Inc.
Four onion maggot sticky traps consisting of three stakes with blue sticky cards clipped above the crop canopy were placed on each side of both fields (Figure 2B). Cards were monitored weekly for natural onion maggot populations as well as for the displacement of sterile / pink flies throughout the growing season. Fly releases began on May 16 and continued weekly until September 11. Flies were released on the north-west corner of the release field at least 30 m from the closest sticky card trap at the west side of the field. Damage plots measuring 30 x 30 cm capturing approximately 100 plants were set up a short distance away from the sticky traps at the flag leaf stage May 29 at each of the four sites per field (Figure 2A). The number of plants were counted weekly until August 7. In addition, 50 onions were harvested every week starting on July 10 and commencing on September 3 to monitor for maggot damage (Figure 2C). The control field was harvested September 7 and the release field was harvested September 14. The final fly release took place September 11 and the final sticky card assessment was on September 19. Weather parameters were measured hourly using a HOBO datalogger U30 RX3000 (Onset Computer Corporation) from April 11 onwards. Weather data from April 1 to April 10 was collected for degree day modeling from a nearby weather station (43.437, -81.654) approximately 12.3 km from the field site. An onion maggot degree day model was used to track the development and predict the generation time of adult flies. Degree day values using a base of 4°C started to accumulate April 1 using the following formula: ((Max Temp + Min Temp)/2) – 4°C.
RESULTS: Sticky card counts throughout the season indicate that the control field had a higher fertile fly pressure than the release field from June 13 until harvest (Figure 3). An average of 2.2 flies/trap/week were counted per trap in the release field compared to 5.4 flies/trap/week in the control (Table 1). Pink flies were found at every trap at the release field but most were quantified throughout the season at the west trap which was the closest trap relative to where the sterile flies were release. No pink flies were found on any of the sticky cards at the control field. Degree day modeling predicted generational peaks for onion maggot fly emergence to occur May 16 (1st Generation, 210DD), July 5 (2nd generation, 1025DD) and August 17 (3rd generation, 1772DD) using the DD model ((Max Temp + Min Temp)/2) – 4°C with values accumulating after April 1st (Figure 4). The emergence peak observed in the field on July 24 was ~19 days after the predicted second generation emergence and ~24 days before the third generation emergence. It is likely that the second emergence peak occurred July 24 and the third emergence occurred between August 15 and August 28 when the sticky cards were compromised due to a weather event. Sticky card trap counts indicated that the main spike in fertile flies at both field sites occurred the week leading up to July 24, (release: 27 flies/trap/week, control: 10 flies/trap/week). The emergence peak observed in the field on July 24 was ~19 days after the predicted second generation emergence and ~24 days before the third generation emergence. Destructive sampling did not find any onion maggot larvae throughout the season. The level of onion maggot damage in these fields this year was low relative to other years (Grower correspondence).
CONCLUSION:
CONCLUSION: Onion maggot (Delia antiqua) management relies heavily on group 1B organophosphates, specifically chlorpyrifos insecticides which have been identified as a major surface water contaminant in some vegetable growing areas. The prospect of insecticide resistance and potential restrictions of use illustrate the importance of alternative management strategies for this insect. Throughout this trial, sticky cards were the only monitoring strategy that could compare insect levels between the two fields since destructive sampling did not find any onion maggot larvae throughout the season. Differences in stand-loss observed by damage plots between the two fields showed a 43% loss in the release field and 28% in the control. Given the higher seeding density of the field, it is likely that competition for space and moisture resulted in the greater stand loss percentage in the release field compared to the control. Overall, both fields were harvested with roughly the same density of onions at harvest between the two fields. Sterile Insect Technology (SIT) in Quebec has proven to eliminate the application of soil and foliar chlorpyrifos insecticides in most fields while maintaining onion yields comparable to pesticide-based programs. Onion acreage in Quebec using SIT has grown from 140 ha in 2011 to 680 ha in 2017. Work in Quebec has shown that the release rates of sterile flies could be decreased by up to 90% within 5 years of repeated use due to the reduction of wild populations while also decreasing the cost of the sterile fly program itself.
If you are interested in applying this management strategy on your farm, please contact Anne-Marie Fortier at afortier@phytodata.ca.
Funding for this project was provided by Pesticide Risk Reduction Program through the Pest Management Centre. Thank you to Hannah Fraser, Cora Loucks, Dennis Van Dyk, Ashleigh Ahrens, Jordan Elshof, Josh Mosiondz, and Laura Stoltz for their help throughout the growing season.
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