Canola growers fear rise of resistant beetle

Striped flea beetle | North Dakota growers are concerned about the insect, which shows neonicotinoid resistance

Neonicotinoids may be causing an insect population shift in North Dakota, says an entomologist.


Producers in the state’s primary canola growing regions are reporting high numbers of striped flea beetles this spring, said Janet Knodel, an extension entomologist with North Dakota State University.


The reports are curious because crucifer flea beetles have long been the dominant pest in North Dakota canola fields.


“This is the first year I’ve received reports of lots of striped flea beetles,” Knodel said, adding the information is coming from north-central and northeastern North Dakota.


Knodel said the species shift worries canola growers because re-search has demonstrated that striped flea beetles are more resistant to neonicotinoid seed treatments than crucifers.


“This (population shift) is a result of one species being more tolerant to an insecticide,” she said. 


“This is kind of an unusual situation … because of the insecticide causing the shift.”


Julie Soroka, an Agriculture Canada entomologist in Saskatoon, said the North Dakota reports aren’t shocking because striped flea beetles are becoming more populous in nearly all regions of Western Canada.


Crucifer flea beetles were the primary species in prairie canola fields 10 years ago with the exception of the Peace River region in Alberta and the northern parkland areas, where striped flea beetles are more common.


Prairie field surveys conducted between 2007 and 2011 found that striped flea beetles have moved south, pushing aside crucifers.


Soroka and Bob Elliott, also of Agriculture Canada, have monitored flea beetles in canola fields at the Sask-atoon research centre since 2003. Crucifer was the dominant species between 2003 and 2009, comprising 97 percent of the population at the centre.


“Since 2009 … we’ve seen quite a shift in the composition of that population,” Elliott said.


“In 2011, for example, the frequency of striped flea beetles jumped from less than one percent to 62 percent of the population … in the early seeded (canola).”


In later seeded canola, striped flea beetles increased from one percent to 36 percent in the Saskatoon fields.


Soroka said neonicotinoid seed treatments are allowing striped flea beetles to take over new geography.


“It is not unreasonable to suppose that neonicotinoids have caused the species shift that we see in prairie canola,” she said in an email. 


Soroka said climate change could also be benefiting striped flea beetles. The species may be able to survive in a wider range of conditions, than crucifers.


“However, climatic factors are difficult to correlate with the flea beetle species shift, and might not occur simultaneously over a large area,” she said. 


Manitoba Agriculture entomologist John Gavloski isn’t convinced a flea beetle species shift is occurring on the Prairies or in North Dakota.


He said striped flea beetles appear earlier in the spring and crucifers dominate in June, which means the timing of seeding will influence the type of beetle detected on canola seedlings.


Knodel said she will need to conduct a more systematic survey to determine if stripes are now the principal flea beetle in the state.