Species identity and local adaptation affect heat stress tolerance more consistently than plasticity in a guild of thrips pests.

Understanding the main factors influencing heat tolerance is critical for predicting pest responses to this stress. Previous insect studies have suggested that heat tolerance may be influenced by species identity, local adaptation, and phenotypic plasticity, with potential constraints among these factors. However, studies that allow the simultaneous partitioning of these effects are rare except in a few model organisms. We address this issue in a guild of four thrips pest. All species followed an injury accumulation model, with Megalurothrips usitatus, Frankliniella intonsa, and Frankliniella occidentalis exhibiting similar coefficients of thermal sensitivity (z = 5.2 to 5.4), while Thrips palmi showed higher sensitivity (z = 6.85), demonstrating a more rapid decline in tolerance with increasing temperature. Common-garden experiments showed significant among-population variation of heat tolerance within each species, with patterns appearing to match local climates. Nevertheless, species identity remained the dominant determinant of heat tolerance when compared to geographical variation. Short non-lethal exposures to heat (hardening) and longer-term exposures (acclimation) produced variable responses depending on species and conditions. Variance partitioning revealed species identity as the dominant determinant of heat tolerance, explaining 22.3% of the total variance, compared with among-population geographic variation (19.4%), Plasticity collectively accounted for 12.05% of the total variance, comprising 4.69% from baseline plasticity and 7.36% from species-specific plastic responses. This multidimensional framework clarifies how genetic differentiation and limited plasticity interact to shape thrips thermal niches and provides a mechanistic basis for predicting seasonal dominance and range shifts of these key pest species under intensifying heat extremes.