Host plant effects on parasitoid attack on the leaf beetle Chrysomela lapponica

Area of Science:

• Ecology
• Chemical Ecology
• Insect-Plant Interactions

Background:

• Leaf beetles like Chrysomela lapponica sequester salicyl glucosides (SGs) from host plants for chemical defense.
• Northern Russian populations of C. lapponica face significant parasitism from phorid flies (Megaselia opacicornis) and tachinid flies (Cleonice nitidiuscula).

Purpose of the Study:

• To compare the suitability of SG-rich (Salix borealis) and SG-poor (S. caprea, S. phylicifolia) willow species for C. lapponica.
• To investigate if enemy pressure on C. lapponica varies across host plant species with differing SG content.

Main Methods:

• Laboratory experiments assessed larval survival and adult body mass on different willow species.
• Field studies monitored parasitism rates by M. opacicornis and Cl. nitidiuscula on beetles from various host plants.
• Laboratory choice tests evaluated M. opacicornis egg-laying behavior on beetles reared on different willows.
• Field enemy-exclusion experiments compared beetle survival with and without natural enemies present.

Main Results:

• C. lapponica larvae showed higher survival and faster development on SG-rich S. borealis compared to SG-poor willows in laboratory settings.
• Field studies revealed significantly higher parasitism rates by M. opacicornis and Cl. nitidiuscula on beetles feeding on S. borealis.
• M. opacicornis did not discriminate between beetles reared on SG-rich or SG-poor willows in laboratory choice tests.
• Enemy exclusion enhanced beetle survival, but no difference was observed between S. borealis and S. caprea, despite higher parasitism/predation on S. borealis.

Conclusions:

• While SG-rich willows benefit C. lapponica development, they do not confer enemy-free space.
• Increased parasitism and predation on S. borealis suggest a trade-off between plant quality and enemy avoidance.
• C. lapponica larvae do not appear to gain a defensive advantage against parasitoids by feeding on SG-rich willow species.