Why does the bud-galling sawfly, Euura mucronata, attack long shoots?

Area of Science:

• Ecology
• Entomology
• Plant-Insect Interactions

Background:

• The bud-galling sawfly, Euura mucronata, exhibits a preference for specific host plant traits.
• Previous research indicates sawfly oviposition may be influenced by host plant characteristics, but underlying mechanisms require further investigation.

Purpose of the Study:

• To investigate the factors driving the preference of Euura mucronata for longer shoots of Salix cinerea.
• To quantify the contribution of larval establishment success and survival to this host selection pattern.

Main Methods:

• Analysis of gall abundance across different shoot lengths in forest, watermeadow, and lakeside habitats.
• Assessment of larval establishment success and survival rates in relation to shoot length, bud availability, gall size, plant resistance, and natural enemy impact.

Main Results:

• Shoot length was a significant predictor of gall density, accounting for 76-93% of variance.
• Larval establishment success (57-77% variance) and post-establishment survival (40-54% variance) were key factors.
• Larval survival was primarily determined by plant resistance, not natural enemies.

Conclusions:

• Euura mucronata preferentially attacks longer Salix cinerea shoots due to higher larval establishment success and survival rates.
• Plant resistance plays a crucial role in larval survival, reinforcing the advantage of longer shoots.
• These factors collectively explain the observed pattern of increased sawfly attack probability with increasing shoot length.