Expanding distribution of an existing parasitoid to new areas for bio-control of cereal leaf beetle in small grain cereals in the Canadian prairies
Project Code: PRR13-020
Hector Carcamo - Agriculture and Agri-Food Canada
To expand distribution of cereal leaf beetle parasitoid Tetrastichus julis in areas where the pest is causing damage but parasitoid is lacking
Summary of Results
The cereal leaf beetle (Oulema melanopus L.) (CLB) is a major threat to cereal production in North America. It was first discovered in the north eastern United States (US) in the 1960’s and it quickly spread to most temperate regions where small grain cereals are produced. In Canada, it was first discovered in southern Alberta in 2005 and by 2015 it was reported in other regions of Alberta, as well as in Manitoba and Saskatchewan. The parasitic wasp Tetrastichus julis, introduced from Europe into the US in 1964 and also released in British Columbia in 2002, is known to be an effective biocontrol agent and a viable option for CLB control.
In areas where T. julis was established, biological control has become a primary strategy to manage CLB and reduce crop damage by this pest. This approach has led to significant reduction in the use of insecticides such as the organophosphate malathion. However, where the parasitoid is not present at sufficient levels and damage is apparent, sprays with an insecticide are the primary control method for CLB in wheat crops.
This project aimed to relocate T. julis into new areas where CLB was reported throughout the prairies. Another objective was to conduct landscape ecology studies to identify attributes which may act as contributing factors for CLB or T. julis establishment or long-term conservation of T. julis and other beneficial organisms.
Agriculture and Agri-Food Canada researchers and collaborators from provincial governments and industry scouted many fields to monitor the spread of CLB and the presence of T. julis in cereal crops throughout the Prairies. Adult cereal leaf beetle numbers were tracked by investigating sweep net captures. Presence of T. julis was determined by examining the incidence of parasitized CLB larvae collected from the target areas. This information was used to choose parasitoid release target sites where parasitism levels were low (0 to 20%). In general, at least 30% parasitism is required for successful biological control to keep a pest below damaging levels.
From 2013 to 2015, adult T. julis wasps and CLB larvae parasitized by T. julis were collected from winter and spring wheat fields with a history of CLB and T. julis presence near Lethbridge. These were then mass reared in growth chambers at the Lethbridge Research and Development Centre (LRDC) to start lab colonies of the parasitoid. Within 72 hours of emergence, the adult wasps were stored in groups of 20 in 500 millilitre plastic salad containers and shipped for release in designated sites.
The landscape ecology study, conducted over the 2014 and 2015 seasons, documented and characterized landscape features for a number of fields surrounding wheat crop sites where CLB and T. julis populations and parasitism of CLB larvae were quantified. Landscapes were characterized based on the percentage of non-cropped areas (including pasture, native and cultivated grassland, and riparian vegetation) and cultivated areas within a 2 kilometers radius to the sampled wheat fields. The percentage of various landscape attributes was then correlated with the observed incidence of CLB and T. julis and parasitism levels.
Annual pest reports generated through this project documented a number of new areas where CLB has spread in the Canadian Prairies, confirming that CLB is still an emerging pest, and a threat to cereal crops. New knowledge of the biology of T. julis and dynamics of its parasitic interactions with CLB in wheat crops was generated through the project as well. More importantly, this work helped to draw growers’ attention to the biological control approach, leading to a growing interest in releasing T. julis instead of using insecticide sprays for CLB control.
From 2013 to 2015, about 14,000 T. julis (90% adults, 10% pupae) were relocated from LRDC to various wheat fields in the prairies where CLB was reported as an emerging threat. In Alberta, releases occurred near Olds, Red Deer, Lacombe, Wetaskiwin, and Edmonton. Most releases in Saskatchewan occurred around Moosemin and Langenburg, and also in the Maple Creek region. In Manitoba all releases occurred around Carman.
About 76 cereal fields were assessed for the landscape study over two years. Preliminary results from the 2014 data (approximately 30 fields), indicate that CLB abundance decreased in cereal fields surrounded by landscapes that had a high proportion of non-cropped habitat. Barley fields in the surrounding landscape appeared to be associated with increased parasitism. Barley may be a preferred host that concentrates CLB, which in turns attracts large numbers of parasitoids. This suggests the benefit of releasing T. julis in landscapes where barley fields are present.
Results from this project and best CLB management practices were communicated to cereal growers throughout the course of the project at presentations at industry meetings, conferences, and field days. A bilingual factsheet Biological control at its best, using the T. julis wasp to control the cereal leaf beetle and several articles in popular agriculture media were published to raise awareness, and promote adoption of biological control for Cereal Leaf Beetle. New information generated on this pest and its natural enemy were also incorporated into the illustrated catalogue Field Guide to Pests and Natural Enemies of Prairie Field Crops published in 2015.
It may be beneficial to conduct post release monitoring of T. julis in areas targeted by this project to assess parasitoid establishment and parasitism success, and to support further re-distribution in new areas. Rearing and relocations of parasitoids will continue for 1 or 2 years, as needed, with the assistance of personnel trained in the course of this project.
For more details, please contact Hector Carcamo, Ph. D.
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