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

## TL;DR

This study reveals how the bark beetle Ips hauseri builds galleries and reproduces in spruce forests, offering insights into its population growth during outbreaks.

## Contribution

The study identifies 11 distinct gallery morphologies and links reproductive output to harem size and tree characteristics.

## Key findings

- Gallery length correlates positively with egg production in Ips hauseri.
- Reproductive output peaks at a harem size of five females per male.
- Larger host trees support more complex gallery systems.

## Abstract

Ips hauseri has long posed a threat to the health of coniferous forests in Central Asia. Since 2020, this pest has caused severe damage in the Hami forest region. However, its cryptic behavior makes it difficult to directly observe the complete reproductive and developmental process associated with gallery construction. Therefore, we systematically dissected its gallery-building process in stages. This study investigates the diverse types of gallery structures and their corresponding adult population dynamics at different developmental time points, examines reproductive development within various gallery structures, and compares the influence of different factors on gallery development. The aim is to gain a more detailed understanding of the gallery system development patterns of Ips hauseri.

Outbreaks of Ips hauseri, a major bark beetle pest in Central Asian Picea schrenkiana 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. hauseri 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.