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Voracious beetles may boost pest control for growers across Canada

The carabid ground beetle, Pterostichus melanarius, has a potentially useful talent – it can consume up to three times its weight in a single day.

The tremendous appetite of this black beetle has drawn the interest of researchers at Agriculture and Agri-Food Canada, who see it as an excellent candidate to help control pests in many field crops across Canada.

The beetle feeds on a wide range of insects and is already a natural predator in many Canadian farmlands, says Dr. Dave Raworth of the Pacific Agri-Food Research Centre in Agassiz, B.C. He and technical staff are studying management strategies that boost beetle populations, to provide growers with more effective, low-cost pest control.

“Growers of field crops often operate with tight economic margins, making it difficult for them to absorb pest control costs,” says Raworth. “Our approach is to determine which predators are already out there providing natural pest control, and to find ways of managing the environment to help those predators do a better job. This may include increasing their populations, or making life easier for them.”

Helping existing predators do a better job is a unique spin on biocontrol, an increasingly popular form of pest control that uses natural predators to control pests. Biocontrol is an important tool for a broader strategy termed integrated pest management (IPM), which involves using a combination of several control measures, to give producers more options for safe, cost-effective and sustainable pest control.

Typically, insects used as biocontrol agents are mass-reared for multiple releases – often an expensive process. Finding simple ways to boost established predators is potentially far more cost effective, says Raworth.

Raworth is focusing on P. melanarius, the most common carabid ground beetle species in agricultural settings in the Fraser Valley. The beetle is about 2 cm long, and 90 percent of its diet is insects. “This species is very well adapted to agricultural environments,” says Raworth. “It is the dominant carabid predator in blueberry, raspberry, strawberry and forage crops.”

Another advantage of this carabid beetle is its wide-ranging appetite, which means it can potentially affect the numbers of several pests at once, says Raworth. The beetle is nocturnal and spends much of its time in leaf litter or in soil where it targets other ground-dwelling insects. The predator’s diet ranges from soft-bodied prey such as weevil larvae and pupae, and leather jackets, to hard-bodied insects such as adult weevils and wireworms.

These beetles are so voracious, they will sometimes eat each other, says Raworth. However, the danger of the beetles eating other beneficial predators is low. Most predators tend to be fast and difficult to catch, whereas plant-feeding pests are slow moving and are easy targets for the beetles.

The benefits of this carabid ground beetle first caught Raworth’s eye seven years ago. Since then, his research team has studied the beetle’s population dynamics, impact on pests, and response to various management practices. Early studies, using onion fly pupae on sticky strips placed in the field, indicated the beetle’s high predatory potential – the beetles devoured 54 percent of the pupae within 24 hours.

Most recently, Raworth and a visiting scientist from Korea developed a model of beetle movement to estimate absolute population sizes in a field, given pitfall-trap catches and average temperature – a tool essential in evaluating the beetle’s impact.

The next steps are to pinpoint what the beetles are eating and examine the effects of different management strategies on beetle activity and populations. Researchers are currently examining the effects of cover crops and manure applications.

“Natural systems are very complex with hundreds of different interacting elements,” says Raworth. “We are trying to tap the strings of this spider-web network of interactions to understand the system, and find ways to benefit growers.”

Integrated pest management and biological control research are part of Agriculture and Agri-Food Canada’s mandate to promote innovation for growth, maintain security of the food system and protect the health of the environment.

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