Gallery Architecture and Reproductive Strategy of Ips hauseri (Coleoptera: Curculionidae) in a Picea schrenkiana Forest: Implications for Population Dynamics Under Outbreak Conditions

Outbreaks of <i>Ips hauseri</i>, a major bark beetle pest in Central Asian <i>Picea schrenkiana</i> forests, have intensified under climate warming and prolonged droughts. However, the reproductive behavior and gallery construction strategies of this species remain poorly understood, limiting our ability to predict its population dynamics. Here, we dissected 219 galleries from infested spruce trees in Hami, Xinjiang, during an outbreak period (2024-2025). We identified 11 distinct gallery morphologies, with harem size (number of females per male) ranging from one to seven. Gallery length was positively correlated with egg production. Reproductive output peaked at a harem size of five, beyond which both gallery dimensions and fecundity declined. Host tree diameter at breast height (DBH) significantly influenced gallery complexity, with larger trees supporting more maternal galleries. Upward-oriented galleries were longer and contained more eggs than downward ones. Intraspecific competition, mediated by gallery adjacency and spatial orientation, strongly affected offspring development. Our results demonstrate that <i>I. hauseri</i> exhibits flexible gallery architecture and reproductive adjustments in response to resource availability and competition-a behavioral plasticity that likely contributes to its outbreak potential. Monitoring gallery morphology and harem size could enhance early detection and population forecasting for this increasingly damaging forest pest.