Project Code: PRR18-010
Project Lead
Anne-Marie Fortier - Phytodata Research Company Inc. and Travis Cranmer – Ontario Ministry of Agriculture, Food and Rural Affairs
Objective
Conduct on-farm demonstration trials using the Sterile Insect Technology for onion maggot control in Ontario onion set fields, and gain knowledge about the distribution and population dynamics of Delia spp. in this region.
Background
The onion maggot (Delia antiqua) is a major insect pest of Allium crops, such as onions, green onions and shallots. Onion maggot damage can cause onion losses up to 30% for Canadian growers. Options for managing this pest are limited due to difficulty reaching the target insects with effective insecticide treatments. Some populations of onion maggot have already shown resistance to some of the active ingredients in these products and chlorpyrifos-based products are scheduled for phase-out in the next few years. Therefore, alternative options are needed for sustainable management of onion maggot in onion crops.
The Sterile Insect Technique (SIT) has been used to manage onion maggot populations since 1981 in the Netherlands. In recent years, SIT has shown great promise for managing this pest in Quebec as well. The Phytodata Research Company has been working on the development and implementation of this technique since 2005. The adoption of this technique has grown in popularity since the first commercial release in 2011, and is now applied to about 988 ha of onion fields in the region, which represents approximately 40% of the onion production in Quebec. Through consultation within the expert working group leading the Pesticide Risk Reduction Strategy for Root Insect Pests of Carrot, Parsnip and Onion, this technology was identified as a viable alternative solution to transfer to other onion growing regions for onion maggot management. This project aimed to demonstrate the efficacy of this technique in commercial onion fields in Ontario over three growing seasons from 2018 to 2020.
Approaches
Commercial fields seeded at a high density for onion set production located near Exeter, and transplanted cooking onions, planted at an average density near Scotland, were used to demonstrate the SIT in Ontario from 2018-2020. Sterilized onion maggot flies were mass-produced and supplied by Phytodata Company. The D. antiqua pupae were reared in Phytodata’s facility in Sherrington Quebec, then irradiated in Nordion’s Gamma Centre of Excellence in Laval, Quebec. After adding a pink colouring to distinguish them from the wild population, the sterilized pupae were shipped weekly to the farm managers and transferred to emergence boxes. Once the pink flies emerged from pupae one to three days later, the pink sterile flies were taken into the field for weekly releases throughout the growing season. Release rates ranged from 100 000 to 115 000 flies per hectare (ha). and varied throughout the season following the natural population curve. Release and control fields were monitored weekly for occurrence of wild (fertile) and sterilized onion maggot fly populations using insect sticky traps. Destructive sampling of 50 onion bulbs was used to assess maggot damage weekly starting mid-season until harvest in September.
Results
Overall, the level of onion maggot damage observed in all onion fields and years included in this demonstration trial was low despite a moderate to high numbers of flies caught at peak time. There was little onion maggot damage observed in 2018 and 2019 relative to previous years, and no damage was observed in 2020 at the flied sites near Exeter. The fertile maggot fly populations in the field sites monitored during this study ranged from 11-27 flies/trap/week at peak times in 2018 and 2019 to 15-160 flies/trap/week in 2020. During the first year of this demonstration, there was a large difference between the 2nd generation fertile fly populations in the release field compared to the control field. At the population peak, the release field had less than 50% of the population of fertile flies compared to the control field. In the second and third years of this demonstration, pest pressure, and differences in populations between control fields and release fields varied between field sites. Several factors, including the distance between field sites, and proximity to untreated onion fields likely contributed to the variance in pest pressure in these fields. These results demonstrate the importance of widespread adoption of this technique in dense onion growing areas. Overall, the results showed that the onion maggot damage in fields from 2018 to 2020 remained low despite varying pest pressure and repeated use of adjacent fields to grow onions three years in a row.
Conclusions
The SIT has been successfully applied in Quebec for control of onion maggot without the need for conventional insecticides for over a decade. The small scale of this demonstration showed promising preliminary results for using SIT to control onion maggot flies in Ontario as well. These results highlight the importance of a coordinated widespread implementation to have success with this technique in dense onion growing regions. A continuation of this program may help to further determine long-term effects of sterile fly release on onion maggot population and its overall effectiveness in reducing the need for chemical treatments to maintain onion yields.