Lygus bug: Profile of a crop pest

The lygus bug is an interesting pest. Native to Canada, adult insects overwinter under plant debris and migrate into crops, including canola, alfalfa, soybeans and sunflowers. Arriving in spring and summer, they lay their eggs on crop stems.

Lygus is a complex that refers to four species: L. elisus (pale legume bug), L. lineolaris (tarnished plant bug), L. borealis and L. keltoni. Populations depend on location and available crop. According to Héctor Cárcamo, research scientist, insect pest management, Agriculture and Agri-Food Canada, L. elisus, L. borealis, and L. keltoni are more often found in the drier parts of the prairies. “If you are in the more humid areas, for example, north of Edmonton and in parts of Manitoba, you get this tarnished plant bug, Lygus lineolaris, as the dominant lygus species,” he said.

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While the species are biologically similar, they have somewhat flexible life cycles in the sense that they can produce more than one generation, depending on temperature. If the weather is warm enough, they can actually continue feeding and laying eggs.

In southern Alberta, for example, L. keltoni have two generations on average. In the Lacombe region, they have about one and a half generations. In the Peace region, they only have one.

Scouting is key to control

In canola, lygus adults and nymphs attack the seeds, buds and flowers, piercing the tissue in order to extract its contents. Once attacked, buds turn white and fail to develop, flowers fall without forming pods or pods fall off without maturing. When the pest feeds on the seeds they tend to darken and collapse or shrink, impacting both quality and viability. According to the Canola Council of Canada’s pest profile, additional loss may occur if flowering is delayed by heavy feeding pressure or drought.

Monitoring for lygus is key. It is recommended that growers take samples at the end of flowering and at early ripening when the temperature is >15 °C. After taking 10 sweeps at 15 sites and recording the cumulative total of lygus at each site, it is recommended that growers refer to provincial government websites for economic thresholds.

Before spraying, Keith Gabert, Canola Council of Canada agronomist, reminds growers that economic thresholds do not take natural predators and beneficial insects into consideration. “We really want to make sure that they understand that there’s a whole lot of insect ecology happening in their field,” he said. “And that a really small percentage of it is pests.”

“There are a lot of natural enemies and predators that are keeping those populations in check,” he said. “Should you choose to wipe the slate clean with an insecticide, that’s generally a bad thing. It needs to be considered a serious decision, not just a quick solution.”

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