The lesser clover leaf weevil (Hypera nigrirostris) is a significant pest in red clover (Trifolium pratense) seed production, yet no economic thresholds have been established to guide its management in North American systems. This study quantified the relationship between larval density and seed yield over two years of replicated field trials in northeastern Saskatchewan. A linear mixed-effects model revealed that seed yield declined by an average of 9.87 kg ha⁻¹ for each additional larva per 10 plants. These data were used to calculate economic injury levels (EILs) and corresponding economic thresholds (ETs) under variable market conditions. Based on a control cost of $53.08 ha⁻¹ and observed field efficacy of 55.9%, EILs were estimated at 4.5, 2.9, and 2.3 larvae per 10 plants under low ($2.14 kg⁻¹), average ($3.31 kg⁻¹), and high ($4.30 kg⁻¹) red clover seed prices, respectively. Final ETs were set at 90% of the EIL to account for scouting variability and population growth, yielding practical thresholds of 4.0, 2.5, and 2.0 larvae per 10 plants. These results provide the first data-driven economic thresholds for H. nigrirostris in red clover seed systems and support the development of integrated pest management strategies that respond to real-time economic conditions. Ongoing work is focused on sequential sampling plan development and temperature-adjusted threshold modelling.
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