Two wireworm experts have developed innovative traps that target the adult stage of wireworms, called click beetles.
Two researchers have done extensive work to improve and expand options for controlling wireworms, including insecticides and crop rotations. However, none of the available options gives complete control, and wireworm populations are exploding in some parts of Canada. New, innovative traps are set to become valuable additional tools in the fight against these very damaging pests.
Wireworms belong to the Elateridae family. Canada has about 30 wireworm species of economic importance. A single field can have several species, and species differ from each other in various ways, including responses to control measures.
In most species, the beetles lay their eggs in the soil in the spring. The larvae hatch from the eggs and live in the soil for about four or five years. Then they pupate and emerge from the soil as adults in the spring.
The larvae feed on the underground parts of plants. They really like cereals and grasses, but if those crops aren’t available, they’ll happily munch on other crops. In potatoes, they damage the seed pieces and, most importantly, they tunnel into the daughter tubers, reducing marketable yields.
The two traps use somewhat different approaches to catching click beetles, and each has its own strengths. Each can be used for gathering information on wireworm populations to help with decisions on wireworm management, and for mass trapping of the beetles. Because wireworms live for several years, mass trapping is a long-term strategy, with annual trapping to reduce the numbers in subsequent wireworm generations.
VERNON PITFALL TRAP
Bob Vernon of Agriculture and Agri-Food Canada (AAFC) in Agassiz, B.C., wanted to develop a more cost-efficient and time-efficient method of trapping beetles. So in 2014, he tested all the existing ways to trap beetles, and condensed all the best features down to create the new Vernon Pitfall Trap.
The trap has two main components: a cup-like base and a lid. “The base, which goes into the ground, is exactly the same dimensions as a bulb planter,” he says. “So you use a bulb planter to pop out a core of soil. Then you put the trap’s base into the hole, step on it [so the top is flush with the soil surface], and it goes right into the ground very securely. And then you put the lid on it.”
The base is designed to hold a specimen cup, the type of cup used for urine samples. When you’re checking a trap, you take off the lid and take out the little cup. Then, if you’re monitoring beetle numbers, you can put a cover on the cup to keep the beetles for counting later, and you put another cup in the base. Or if you’re doing mass trapping, you can dump the beetles into a container for later disposal, and put the cup back in the base.
The lid has little vertical pins extending from the lid to the base, to allow beetles in and keep rodents out. “You don’t want rodents getting into your traps and possibly dying there because they can’t get out, or chowing down on your specimens,” explains Vernon. The lid is also designed to keep out water.
The lid can hold a little plastic cylinder containing a pheromone for species-specific trapping. Pheromones are available for the three European click beetle species that have come into Canada in the last century or so.
“Two of those species, Agriotes lineatus and Agriotes obscurus, are huge problems in British Columbia. And the other species, Agriotes sputator, is an enormous and growing problem in Prince Edward Island,” says Vernon.
In these species, the females produce pheromones to attract males, not vice versa, so the pheromones attract only males to the trap. The pheromone lure gradually releases the pheromone, which reaches about five to 10 metres.
Without the pheromone lures, the trap will catch both males and females of any insects wandering around on the ground, so it can be very useful for studies of insects such as ground beetles.
Vernon’s research team tested the Vernon Pitfall Trap in 2015 and 2016 in P.E.I. and B.C. using the pheromones. “In 2015 in P.E.I., we caught just under one million Agriotes sputator males in three fields. We caught over 7,000 in one trap in six days in one of the fields. This year, one of our traps caught over 22,000 beetles on one farm,” he says.
“We found that the new traps are as good as or better than the existing traps for capturing the beetles, plus they take about one-tenth of the time to install and inspect. Also, the trap costs about $1 to manufacture, and most of the other available traps cost more than $10 per trap. And it is very durable – you can use it probably for decades.”
Vernon sees several ways growers might use the traps. “The traps can be used as ‘sentinel traps’ to determine if the three European species are in an area. For example, this year in P.E.I. we used the traps in about 400 different locations to determine whether or not the devastating species Agriotes sputator had invaded those areas at the present time. That is very useful information for farmers.”
The traps can also be used to monitor population levels of the three species. He explains, “If a farmer collects the click beetles every week from a sentinel trap, he can tally how many click beetles were caught in that trap in that growing season. That would tell him whether the population in that area is just getting going or whether he might want to take some control measures or avoid planting potatoes.
“We’re currently working to determine thresholds – how many click beetles in the sentinel traps would indicate that you have to do something about the European click beetles in that area.”
Vernon’s group is also developing a click beetle measuring cup so users can dump all their captured click beetles into this cylinder, and the graduations on the cylinder will give a quick-and-dirty count of the beetle numbers.
Because the traps are inexpensive, growers could use them for mass trapping to reduce egg laying in certain chronic areas. “In some trials in B.C., we’ve found that if the traps are spaced about 10 metres, you can take out about 80 per cent of the male population [of the target click beetle species] in an area.”
For mass trapping, he recommends placing traps in the grassy areas surrounding crop fields. He also advises putting the traps out early – for example, late March in B.C. and late April in P.E.I. – to catch male click beetles as soon as they start becoming active and before they mate.
AAFC is in the process of licensing the Vernon Pitfall Trap technology to a B.C. manufacturer. And Vernon’s research group is looking into local options for producing the pheromone lures.
“I’m very excited about the trap,” says Vernon. “We’re already using the traps in P.E.I., and some larger growers are using them as sentinel traps so the technology is already being used. I have also been inundated with requests for the traps; they’re now being used in almost every province in Canada as pitfall traps to collect beetles to see what’s out there. Scientists who do a lot of pitfall trapping love the new trap because it’s so easy to use.”
NELT – NORONHA ELATERID LIGHT TRAP
Christine Noronha, with AAFC in Charlottetown, P.E.I., has taken a different approach to click beetle trapping. Her priority is to catch female click beetles.
“Catching the females is a good way of decreasing the number of eggs that are laid and reducing future generations. There are more males than females in the click beetle population, so the pheromone traps usually catch a lot more beetles. But it only takes a few males to have a growing click beetle population because the females mate several times and each time they mate they lay about 50 to 100 eggs. So the population can go up pretty fast.”
Instead of pheromones, her trap uses a light to attract click beetles. She explains, “For quite a few years, I had an idea about building a light trap for click beetles because a lot of insect species are attracted to light. But it didn’t seem very feasible at that time because a light in a farm field would need a power source, like a battery or generator. Then one day I was walking through a hardware store and saw a solar-powered spotlight. From my previous experiences with insects, working with them and trapping them when I was young, I knew I needed a spotlight – something bright and focused – not just an ordinary garden light. So I thought I’d try these solar-powered spotlights. And when I did, I was just amazed at how many beetles we were catching.”
Her trap is called NELT, the Noronha Elaterid Light Trap.
It has a 20-cm round plastic base with a cup holder and an adjustable 2.5-cm post. The base and holder are buried to a depth of 2 cm in the soil. The collection cup is 16-ounce cup that is white on the inside. The cup is placed in the cup holder so that its rim is even with the soil surface. The solar-powered spotlight is placed on the post and adjusted to ensure the light shines in and around the cup. A quarter cup of water and a few drops of soap are added to the collection cup to kill beetles as they fall in.
The trap is surrounded with poultry wire to prevent mice and beneficial insects from falling into the trap, although it is not essential. She explains, “You may not want to use the wire mesh if you don’t know which click beetle species you have; if one of the bigger species is in the area, it may not be able to go through the wire mesh.”
To check the trap, you remove the collection cup and then either just discard the contents or keep them so you can count and/or identify the dead beetles later.
NELT can be used to see which wireworm species are coming into a field – not just the European species – and to monitor relative population levels of the various species, and also for mass trapping. Noronha notes, “Buying the traps would be a one-time investment. You put them in the field in the spring for a two-month period when the beetles are active, and then remove and store them. They can be re-used year after year.” She adds, “It’s best to keep the traps in the field for about two months because you don’t know exactly when peak beetle emergence happens.” The timing of click beetle emergence is influenced by the species involved and spring temperatures.
Noronha first tested her trap in 2015 in two P.E.I. fields. “We had 10 NELTs in one field with a very heavy wireworm population, and we caught over 9,000 beetles compared to 3,000 caught in the traps with no light. The second field confirmed these results.”
They determined the sex of the click beetles in the traps and found significantly high numbers of females in the NELT.
In 2016, Noronha’s research team continued testing the trap in P.E.I. They evaluated it in potato, grain and clover fields, and found it worked in all these crops. They’ve also started collecting data to determine how widely spaced the traps need to be. And they’re experimenting with options for where to set traps in a field.
In P.E.I., the NELTs are capturing at least four click beetle species. Usually Agriotes sputator is by far the most common species, but traps are also capturing high numbers of another invasive pest species as well as native Canadian species.
Also in 2016, NELT testing was initiated in New Brunswick and Nova Scotia, and some short tests were done in Ontario, Alberta and British Columbia. Noronha’s team is currently determining the sex and species of the click beetles captured in these other provinces; wireworm species vary from region to region across Canada.
Next year, Noronha hopes to do more comprehensive testing in the other provinces, including light versus no-light comparisons and keeping the traps out for the whole egg-laying season.
AAFC has licensed the NELT technology to a P.E.I. company. According to Noronha, the company hopes to have traps available for growers early in 2017.
“I’m quite happy with how the trap works and the fact that it is catching females. I think it’s something that is feasible for growers to combine with their other wireworm management strategies,” she says. “If we take out the females using this trap, it will help the growers reduce the wireworm population faster. That’s important because the wireworm population on the Island is really, really high right now.”