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Warming climate = new pest threat?

The pollen beetle larvae feed inside the canola bud. Photo by CÉROM.

The pollen beetle may look like a cute little bug, but it’s one of Alberta’s “most unwanted” pests. “It is one of those pests that we don’t have now but could have a fairly major impact on the canola industry,” says Scott Meers, insect management specialist with Alberta Agriculture and Forestry.


July 5, 2016
By Janet Kanters


Topics
The pollen beetle larvae feed inside the canola bud.

In Europe, this beetle species (Brassicogethes viridescens) can cause serious yield losses in spring-planted canola crops. The adult beetles feed on canola pollen and buds, and the larvae feed inside the buds and open flowers, destroying the ability of the flowers to produce seeds.

So far in Canada, the pest is found only in the Maritimes and Quebec, but climate models show it could survive and even thrive in canola-growing regions across the country.

The good news is that researchers in Eastern Canada are already tackling the pollen beetle problem. “We’re actively working on this problem, and our goal is to try to have the tools ready to manage the pest before it becomes a crisis in Canada,” says Peter Mason, an entomologist with Agriculture and Agri-Food Canada (AAFC) in Ottawa.

Recent increases
The adult pollen beetle is about the size of a flea beetle and is black with a metallic greenish tint. It was first recorded in Canada in the 1940s in Nova Scotia. In a study in the mid-1990s, scientists found numerous pollen beetles in patches of wild radish (a cousin of canola) in Nova Scotia and Prince Edward Island. By 2001, the pest had spread into Quebec as far west as Saint-Hyacinthe.

In P.E.I., the beetle’s recent population levels appear to be linked to the amount of canola grown there. “A few years ago, canola production started increasing on the Island and we started to see more beetles. But canola production has really gone down now, and although we still have quite a few pollen beetles, the populations are not overly high,” says Christine Noronha, an entomologist with AAFC at Charlottetown.

When the beetle populations were very high, Noronha observed serious damage on infested canola crops. She adds, “One of the crops that can be grown to reduce wireworm populations is mustard, which belongs to the same family as canola. Because of the wireworm problems that we have, we might see an increase in pollen beetle populations because of increased mustard acres.”

In Quebec, other factors in addition to the number of canola acres may be playing an important role in the beetle’s population levels. According to Statistics Canada, the area seeded to canola in Quebec has fluctuated up and down over the past 10 years, ranging from 15,200 to 48,200 acres, with 29,700 acres in 2015. However, only recently has the beetle’s population surged.

“We began to see the pollen beetle in high numbers only in the last two or three years. Before that, it was just a species that we observed,” notes Geneviève Labrie, an entomologist with the Centre de recherche sur les grains Inc. (CÉROM). She suspects this recent population increase might be associated with warming climatic conditions that favour the beetle.

Her research shows the beetle is most common in the Bas Saint-Laurent area, a region in eastern Quebec along the St. Lawrence River. This is the third-most important canola production area in the province. Labrie says, “About 2011, the pollen beetle appeared for the first time in that area, and now there’s a huge population. Between 2012 and 2015, we observed a 58 per cent increase in population in that area.”

The pollen beetle is also in the Saguenay–Lac Saint-Jean canola-growing region, which lies about 200 kilometres north of Quebec City. However, the pest is not yet in Abitibi–Temiscamingue, the province’s most important canola production area. Labrie notes, “The beetle could cause big problems if it arrives there.” Abitibi–Temiscamingue is in northwestern Quebec and is adjacent to Ontario’s Temiskaming area, another region where canola is grown.

Westward spread
Mason led a study published in 2003 that modelled the beetle’s potential distribution across Canada. Using long-term average weather data from 1961 to 1990, the model showed that Canada’s canola-growing regions have suitable to very favourable conditions for the beetle.

“Under present climate conditions, there is great potential for the beetle to move west into canola-growing regions in Ontario as well as the Prairies and, of course, that is what we really fear,” Mason says.

AAFC’s Owen Olfert and Ross Weiss have evaluated the effects of a range of possible future climate scenarios on the pollen beetle’s potential distribution and abundance. The modelling results indicate that if Canada’s climate were a few degrees warmer, then conditions would be further improved for the beetle in many areas, including much of the Prairies.

Given that the beetle could survive in Ontario and the Prairies, how might it get there? Mason says the possibility of storm events carrying the beetles westward is remote because our weather events generally move from the west to the east. He thinks the most likely pathway would be human-assisted transfer, with the beetles hitchhiking on plant materials being carried on trucks or trains.

At present, the beetles don’t seem to be migrating into new areas very quickly under their own power, possibly because Eastern Canada doesn’t have the large expanses of canola production that are common in parts of the Prairies.

Mason notes, “The beetles have the potential to disperse on other species of brassica that they might feed on or if canola areas are kind of connected. For example, at the present time not much canola is grown from Saint-Jean-sur-Richelieu in southern Quebec through to south of Peterborough in Ontario. So there is really no way that the beetle can move from canola crop to canola crop.”

Other brassica species include weeds like wild radish, stinkweed, shepherd’s purse and wild mustard, and crops like mustard, broccoli and Brussels sprouts. Labrie notes that a four-year survey on wild brassica plants along roads in western Quebec and southeast of Ottawa in June and July did not find any pollen beetles on the wild plants. Noronha is planning to examine the role of other brassicas in the beetle’s life cycle and population patterns in P.E.I.

Biology matters
Noronha and Labrie are studying the beetle’s life cycle and how it relates to canola growth stages in P.E.I. and Quebec. “The adults come out of hibernation early in the spring and feed on the pollen of different plants, but the larva can only survive on brassicas. The adults come into the canola crop only when they are ready to lay their eggs,” Noronha explains. “[In P.E.I.], the arrival of the pollen beetle in the canola crop is usually synchronized with the time when the flower buds are just forming on canola. Once the adults come into the canola crop, they will stay there and start feeding.”

The females lay their eggs in the flower buds, usually about two to three eggs per bud. After hatching, the larvae feed in the bud. Noronha says, “The larvae are really tiny. They have two larval stages, or instars, compared to some insects that can usually have four or more instars. So the [pollen beetle] larvae have quite a fast development.” The mature larvae fall to the ground and then pupate in the soil. They emerge as adults later in the summer and feed on the pollen of various plant species until they go into hibernation for the winter.

In Quebec, the beetles arrive in the canola crop a little later than in P.E.I. Labrie says, “Fortunately, in Quebec at present, the pollen beetle’s life cycle is not synchronized with the sensitive stage of canola [which is during stem elongation as the buds appear]. The canola plants are very sensitive to pollen beetles at that stage because the beetle puts the eggs inside the bud, and the larva will feed inside the bud and there will be no flowers at all.”

Instead, the beetles tend to arrive in Quebec canola fields between 10 and 30 per cent flowering. At that crop stage, a lot of pollen beetles would be needed to cause significant yield losses. However, Labrie worries that warming climatic conditions might enable the beetle to adjust its life cycle so that it would arrive in canola fields right at the sensitive crop stage, with the potential for very significant crop damage.

Noronha and one of her graduate students have been examining the effect of temperature on the timing of the insect’s life cycle. “We’re trying to develop a degree-day model to see when the beetles emerge from hibernation and when they come into the canola crop, and whether that is related to temperature. We got some really good results [in 2014]. We did it again last year, but it was a strange year – we still had snow on the ground into May and June. So we’re going to do it again in 2016 to make sure our degree-day model is correct.”

Developing control options
Labrie, Noronha and Mason are collaborating on a number of studies to develop integrated pest management strategies for controlling the beetle.

No insecticides are currently registered for use on pollen beetles in Canadian canola crops, so Labrie and Noronha have been testing different active ingredients to see which ones are most effective. Labrie adds, “The pollen beetle is a species that can become insecticide-resistant very rapidly; in Europe, it is resistant to a lot of insecticide products. So insecticide rotations will be important.”

Insecticide timing is also a crucial issue. Noronha explains, “You have to use the insecticides very judiciously because bees forage in flowering canola crops. So you cannot apply the insecticides when the flowers are open. We’re trying to figure out the very short application window to reduce bee exposure.”

Labrie is leading a study to determine the economic threshold for controlling the beetle. Results so far indicate that about three to nine pollen beetles per plant would be needed at the sensitive crop stage to cause serious yield impacts. In Quebec at present, the beetle numbers at the sensitive crop stage are not that high.

In some preliminary observations, Noronha has noticed that larval damage seems to be causing increased green seed counts, rather than outright yield losses. Noronha explains, “If some of the buds die, then canola could compensate by developing more buds. But because those buds are developing later, they won’t mature at the same time as the rest of the crop.” Labrie observed a similar type of response from canola when she introduced pollen beetles into cages at the beginning of the flowering period. Green seeds are a downgrading factor for canola, so Noronha is planning to look into the green seed counts in infested plants.

The researchers are also assessing possible non-chemical control options, such as using trap crops or the beetle’s natural enemies.

Labrie and Mason have been investigating parasitoid and predator species in canola fields in Quebec and Ontario. Mason says, “A number of parasitic wasps attack the pollen beetle in Europe. Geneviève’s work has demonstrated that we do not have any parasitic wasps attacking the beetle’s larval stages here. So there is a good prospect to import a natural enemy from its native range and introduce it here to assist in control of the beetle. However, that process will take some time because we have to make sure the parasitoid is not going to attack our native species, and there are some very rigorous studies that are required.”

The researchers have identified a long list of predator insects and spiders in Quebec and Ontario canola fields. Ground beetles are a key group. “Ground beetles are voracious predators. They are in all of our agricultural systems and in native habitats as well,” Mason explains. “When the mature larvae of the pollen beetle drop to the ground and pupate in the soil, these ground beetles will feed on them.”

The researchers are in the process of evaluating how much impact these predators are having on pollen beetle populations. Labrie says, “My master’s student did lab trials with three ground beetle species: Pterostichus melanarius, Harpalus rufipes and Clivina fossor. The first two are big generalist predators observed in every field, while the third lives in the soil. These three species consumed larvae of the pollen beetle; however, the first two were better at consuming the larvae at the soil surface, while the third one consumed them at a low level under or at the surface. In fact, the pollen beetle larvae go under the soil surface between two and eight minutes after falling off the plant to pupate, so they are well protected from generalist predators.”

Prairie arrivals?
Meers suggests that Prairie crop growers and agronomists keep an eye out for the pollen beetle. If you see an insect that could be a pollen beetle, capture it in a container and freeze it, and record where you captured it. Then contact your provincial pest lab or an entomologist to have the specimen identified. Early detection of the beetle’s arrival on the Prairies could help in controlling the little beetle before it becomes a big problem.