A team of international researchers, including CABI’s Dr Tim Haye, suggest that the life table of the diamondback moth (Lepidoptera: Plutellidae) in Ontario, Canada, has been largely unaffected by changes in urbanisation, crop diversity and climate over the past 65 years.
The scientists believe that mortality rates of the pest – which attacks a range of crops including canola, broccoli, Brussel sprouts, cabbage and cauliflower – have remained consistent at the hands of its three main predators, the larval parasitoids D. insulare and M. plutellae and the pupal parasitoid D. subtilicornis.
Lead author Tina Dancau from Carleton University and Dr Naomi Cappuccino and Dr Peter Mason of the Ottawa Research and Development Centre, Agriculture and Agri-Food Canada, and Dr Haye sought to see if the population dynamics of the diamondback moth had changed since seminal scientist D.G Harcourt developed the first of 74 life tables of the pest in 1954.
However, after the team returned to the Central Experimental Farm in Ottawa, Ontario, where Harcourt conducted his research, to conduct comparative experiments over the summers of 2016 and 2017, they found that total mortality and parasitism levels remained similar.
The only notable difference was that more diamondback mortality could be attributed to predation. This was highlighted using a modern sentinel-based approach, with an enemy-exclusion cage treatment. This method was in addition to the destructive sampling of mature cabbage plants similar to Harcourt’s approach.
The researchers argue, in the new paper published in the journal The Canadian Entomologist, that the diamondback moth is a pest in Western Canada – mainly attacking canola which is worth an estimated $26.7 billion annually to the Canadian economy. Major outbreaks in 1995 and 2001, for example, resulted in the spraying of pesticides on 1.25 and 1.85 million hectares of canola respectively.
The diamondback moth attacks a wide variety of Brassica crops globally – having likely been introduced to North America from Europe around 150 years ago. Populations regularly infest canola in the Canadian Prairies where there has been a major economic impact.
In some regions this pest has become resistant to chemical insecticides – limiting the options available for farmers to control it and reduce the damage caused to their crops and, ultimately, their livelihoods.
In respect of temperature changes over the five decades since Harcourt’s studies, southern Canada and southern parts of Ontario in particular, the scientists state, have experienced fewer days with extreme low temperatures and more days with extreme high temperatures in winter and spring.
As the diamondback moth is considered a seasonal migrant, it is unable to tolerate typical winter conditions in Canada. But the scientists suggest that projected higher temperatures by 2070 are likely to favour the pest over D. semiclausum – reducing the efficacy of this important biological control agent over much of eastern Australia.
This study provides an insight into a system that appears to have changed little after 65 years. The findings could aid management initiatives moving forward for introductions of new exotic biological control agents for diamondback moth in Canada and perhaps elsewhere.
Full paper reference
Dancau, T., Haye, T., Cappuccino, N. and Mason, P.G., ‘Something old, something new: revisiting the diamondback moth (Lepidoptera: Plutellidae) life table after 65 years,’ 2019, The Canadian Entomologist. DOI: 10.4039/tce.2019.70
This paper is available as an open access document here: https://www.cambridge.org/core/journals/canadian-entomologist/article/something-old-something-new-revisiting-the-diamondback-moth-lepidoptera-plutellidae-life-table-after-65-years/A6D33099BFE6430CA9556A35073038C9
Agriculture and Agri-Food Canada provided funding for this project.
Find out more about CABI’s work regarding the biological control of diamondback moth in Canada.