At one time a citizen militia made up the core of Canada’s armed land forces. Effective as it was fighting our more southerly neighbour, though, it was eventually replaced by a more professional standing army.
In the war against pests, researchers are trying to help greenhouse growers do the same. That is, introduce pest-fighting beneficial insects and keep them there full-time – rather than purchasing more each time a problem arises.
Results from a joint project between Agriculture and Agri-Food Canada (AAFC) and the Ontario Greenhouse Vegetable Growers indicate strategic investments in better and more economically-efficient nutrition for beneficial insects can help maintain “a standing army at the ready” to protect against harmful pests – even when the pest, also the main food source for those beneficial insects, is scarce.
Adapting strategies for Canadian growers
Roselyne Labbé, greenhouse etymology scientist at AAFC’s Harrow Research Station, says the project analyzed how different “supplemental foods” helped improve the longevity and competitiveness of beneficial insect populations commonly employed as part of Canadian greenhouse integrated pest management strategies.
Three main supplements were analyzed: Artemia cysts (also known as brine shrimp or “sea monkeys”), Ephestia eggs (moth eggs), and pollen. Similar research conducted in both Europe and Israel, she says, shows each product can have lasting impacts on beneficial insects.
However, Canadian growers don’t use the same beneficial insects as their European counterparts.
“This is where we have an issue. In Europe and Israel, they have a certain set of bugs that are native to the region. They use them, it works really well, but we’re not sure how these kinds of supplemental foods are actually going to work for our native bugs,” says Labbé.
“They’re related species, but not quite the same, so we needed to test the different bugs and the different combinations of foods to see what would be the responses to them.”
Two species native to Canada were tested: Dicyphus hesperus, and Orius insidiosus (minute bug, or flower bug). Labbé says the former, which establishes well in tomatoes, is used by 90 to 100 per cent of Canadian tomato greenhouse growers.
The latter works well in peppers and is used by about 50 per cent of growers producing that crop. Other greenhouse vegetable producers also use these bugs, as do ornamental flower growers.
“They actually eat a huge number of pests,” Labbe says, adding that they’re a particularly effective control for white flies and thrips, two common greenhouse vegetable pests.
Promising results, mixed cost levels
Project results indicate both beneficial bugs respond well to Artemia, Ephestia, and pollen, though to varying degrees. Labbé says Ephestia, which is rich in protein and fatty acids, works very well overall and was particularly beneficial to the Orius bug.
Unfortunately, Ephestia isn’t cheap – it costs $2 per gram. With about three grams needed per square metre of crop, costs can quickly add-up. For this reason, Labbé says it’s important to use Ephestia in a targeted way.
“You can also use it in small amounts where the insects are released,” she says.
At seven cents per gram, Artemia is a more economic choice for wider greenhouse use, with the Dicyphus bug responding very well to it.
Pollen is another cheaper food supplement option that can be introduced by having other flowering plants in the greenhouse, or just spraying pollen itself.
“The problem is some of the pests, like thrips, also like pollen,” she says. “You wouldn’t want to amplify the wrong population.”
Labbe says experiments are ongoing to learn the optimal amounts of each supplement.
Application tactics, incorporation concerns
European and Israeli growers already using pollen, Ephestia, and Artemia (particularly the latter supplement due to its comparatively low cost) generally apply them via a blower or sprayer. Labbé says this works, but also leads to loss as product misses target areas. There is some work – largely from Israeli researchers – showing food-laden ribbons strung between crop rows might be a better way of distributing food supplements.
Growers looking to incorporate a food supplement management strategy also must be mindful of what pest-management controls they are already using. The Orius bug, says Labbé, is particularly sensitive to insecticides; even residues can have a long-lasting impact on establishment.
“This can be an issue for growers in transition,” she says.
She adds the food supplements and beneficial insects studied in the project were generally found to be compatible with other microbial controls used in Canadian greenhouses.
The entire project summary and results are available for free online by searching for nature.com and Orius insidiosus.