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<Emphasis Type="BoldItalic">Key message</Emphasis> <p><b>Larger trees with greater crown volume and higher foliage density attract more PPM egg clutches, highlighting the importance of tree health.</b></p> Abstract <p>The pine processionary moth (PPM), <i>Thaumetopoea pityocampa</i>, is a major pest across North Africa and southwestern Europe, where its larvae cause severe defoliation and long-term damage to pine forests. Female PPMs select host trees for egg deposition using a combination of visual, chemical, and tactile cues, with tree size, vigour, and canopy development playing prominent roles. Larger, healthier trees with abundant foliage generally provide more suitable environments for larval development, offering greater food availability and more stable microclimatic conditions. Beyond tree size, the structural characteristics of foliage—particularly needle size and density—may also influence host selection by affecting both resource quality and the suitability of oviposition sites. Despite previous research emphasizing the importance of tree vigour for PPM oviposition, the relative contribution of tree-level traits versus fine-scale needle characteristics remains poorly understood. To address this gap, we examined host selection patterns in Aleppo pine (<i>Pinus halepensis</i>) by assessing tree traits (height, diameter, crown volume) and needle traits (length, density) across 104 trees at five sites in Algeria. Our results show that larger trees with greater crown volumes hosted significantly more egg clutches and nests, confirming the primacy of tree size in PPM host preference. Needle length, however, had no significant effect on oviposition. In contrast, higher foliage density was associated with a greater number of egg clutches, although it did not influence nest abundance. Overall, these findings underscore the importance of tree size, canopy structure, and foliage density in shaping PPM host selection and suggest that promoting tree health and managing stand structure may help mitigate PPM impacts on Aleppo pine forests.</p>

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Effects of tree size and foliage structure on egg-laying patterns of the pine processionary moth in Aleppo pine forests

  • 期刊论文

  • 发表日期：

    2026年2月21日

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  • Mouffek Guadguad,
  • Mohamed Sbabdji,
  • Xoaquín Moreira

摘要

Key message

Larger trees with greater crown volume and higher foliage density attract more PPM egg clutches, highlighting the importance of tree health.

Abstract

The pine processionary moth (PPM), Thaumetopoea pityocampa, is a major pest across North Africa and southwestern Europe, where its larvae cause severe defoliation and long-term damage to pine forests. Female PPMs select host trees for egg deposition using a combination of visual, chemical, and tactile cues, with tree size, vigour, and canopy development playing prominent roles. Larger, healthier trees with abundant foliage generally provide more suitable environments for larval development, offering greater food availability and more stable microclimatic conditions. Beyond tree size, the structural characteristics of foliage—particularly needle size and density—may also influence host selection by affecting both resource quality and the suitability of oviposition sites. Despite previous research emphasizing the importance of tree vigour for PPM oviposition, the relative contribution of tree-level traits versus fine-scale needle characteristics remains poorly understood. To address this gap, we examined host selection patterns in Aleppo pine (Pinus halepensis) by assessing tree traits (height, diameter, crown volume) and needle traits (length, density) across 104 trees at five sites in Algeria. Our results show that larger trees with greater crown volumes hosted significantly more egg clutches and nests, confirming the primacy of tree size in PPM host preference. Needle length, however, had no significant effect on oviposition. In contrast, higher foliage density was associated with a greater number of egg clutches, although it did not influence nest abundance. Overall, these findings underscore the importance of tree size, canopy structure, and foliage density in shaping PPM host selection and suggest that promoting tree health and managing stand structure may help mitigate PPM impacts on Aleppo pine forests.