Lygus bug and faba bean interaction with environment
Lygus populations varied from year to year and by geographic location. More rainfall in the grey and moist black soil zones resulted in lower Lygus abundance.
The Lygus genus is a diverse group with over 11,000 species, with four species being important pests on the Prairies: L. lineolaris, L. keltoni, L. elisus, and L. borealis. Common hosts include canola, faba beans, soybeans, sunflowers, and many other crops and weeds.
Lygus feeding during the pod stage of faba bean is particularly damaging because the piercing mouth parts cause hull perforations, seed discoloration, and pitting. This can lead to seed quality downgrading.
A research study was conducted to assess Lygus abundance in faba bean and the interaction with cumulative growing degree days, geography and precipitation. The objective was to develop a better understanding of the population dynamics of the pest as influenced by environment.
Surveys were conducted from 2019 to 2023 to assess the incidence and severity of Lygus infestations in faba bean across Saskatchewan. They were done in conjunction with the Saskatchewan Pulse Growers, the Saskatchewan Ministry of Agriculture, and the Entomology Laboratory of the University of Saskatchewan. Sweep net sampling was conducted when 20 per cent of faba bean pods had reached typical length (BBCH 72). Ten samples per field were collected along a ‘W’-shaped transect pattern. The number of fields sampled varied by year ranging from a low of 11 fields in 2022 to 23 fields in 2019.
Life stage, adult species, and adult sex were identified for the collected Lygus.
Maximum and minimum temperatures, total precipitation, total days of precipitation, and cumulative growing degree days were collected during the survey period from Environment Canada’s climate database. Soil climatic zones and crop district were included in the assessment of environmental drivers on Lygus infestations. Statistical analysis was conducted to see how these factors affected Lygus species and abundance.
Species composition
Lygus lineolaris favoured warm and wetter environments, except in very wet soils. Lygus elisus had reduced abundance in the moist black soils zone in high moisture conditions, but the research found that it may tolerate a wider range of environmental conditions.
Lygus borealis also preferred warm and wet environments, but it had a negative effect on abundance in the grey and moist black soil zones.
Lygus keltoni abundance was greater with higher precipitation and the interaction with cumulative growing degree days, but populations fell in the grey and moist black soil zones under high precipitation.
While GDDs was not a significant factor in overall Lygus abundance, it did have a strong positive effect for L. lineolaris and L. borealis with higher GDDs increasing abundance.
Year and crop district significantly influenced species composition. Year explained 22.77 per cent of the variation in species, and the year by crop district interaction explained 40.74 per cent of species composition.
The researchers anticipated that crop district would be a significant factor in Lygus populations, since the fields studies often took part in different crop districts each year. In many cases, faba bean were the last green crop available, and Lygus movement from other maturing crops was likely.
There was a significant interaction between total precipitation and grey and moist black soil zones, indicating that more rainfall meant lower Lygus abundance in these zones.
The researchers concluded that “the significant interaction between the year and crop district underscores the importance of considering both temporal and spatial dynamics when examining Lygus distributions. This suggests that management strategies must be flexible and account for local crop conditions.”
Financial support was provided by the Saskatchewan Pulse Growers, Western Grains Research Foundation, and the Saskatchewan Ministry of Agriculture.
Teresa Aguiar-Cordero and Sean Prager. 2025. Environmental drivers of Lygus species distribution in faba bean fields across Saskatchewan (2019–2023). Canadian Journal of Plant Science. 105: 1-9. https://doi.org/10.1139/cjps-2024-0243
Photos courtesy Teresa Aguiar-Cordero
