Population response of Helicoverpa armigera and Frankliniella occidentalis to air temperature, humidity, and adult density in arid regions of Northwestern China: a statistical association and threshold analysis

Introduction This study investigates the influence of key meteorological factors—air temperature, relative humidity, and near-surface (5 cm) soil temperature—on population fluctuations of Frankliniella occidentalis (western flower thrips) and Helicoverpa armigera (cotton bollworm) in sunflower cultivation zones of arid Northwestern China. Methods Field data were collected from 2023 to 2024 in Beitun City and surrounding sites in Xinjiang, aligning pest occurrence records with localized meteorological monitoring. Statistical frameworks included partial correlation analysis, principal component analysis (PCA), and both linear and nonlinear regression modeling. Results The study revealed distinct stage-specific ecological responses. F. occidentalis density during the budding stage showed a strong positive correlation with air temperature (r = 0.7300, p < 0.05), fitting the Robust Index Increment Model (R² = 0.9577) within a temperature-sensitive range of 23–30°C. Conversely, H. armigera populations were predominantly driven by humidity during early stages (r = 0.7400, p < 0.05), with later stages influenced by combined thermal and moisture thresholds. The H. armigera population exhibited strong positive correlations with both air temperature and relative humidity, with a maximum partial correlation coefficient of r = 0.8400. At the flowering stage, air temperature and humidity accounted for 57.89–60.42% and 23.61–29.26% of ecological variation, respectively (regression analysis). Threshold analysis indicated that during the sowing period, the combined condition of air temperature ≥ 24°C and relative humidity ≥ 40–50% is the key ecological threshold range leading to a significant increase in H. armigera populations. This threshold is a statistical correlation range based on observational data from specific years and locations; its specific boundary values (especially the humidity lower limit) may carry a confidence interval. Discussion This threshold provides an important reference for early warning in this region, though its universality and stability require further validation under broader climatic conditions, soil types, and cultivation management practices. Moreover, the influence of meteorological factors on pest population dynamics shows obvious interspecific differences and stage-specific effects. Air temperature emerged as the primary limiting factor for F. occidentalis , whereas H. armigera populations were synergistically influenced by both air temperature and relative humidity.