Preference for protected feeding sites by larvae of the willow-feeding leaf beetle Galerucella lineola

Authors


STIG LARSSON Department of Entomology, Swedish University of Agricultural Sciences, PO Box 7044, S-750 07 Uppsala, SwedenStig.Larsson@entom.slu.se

Abstract

1. Free-living insects are often thought of as more vulnerable to environmental hazards than concealed insects, such as galling or mining insects. The possibility that larvae of the free-living leaf beetle Galerucella lineola seek out existing plant structures and thereby become partly concealed was explored.

2. Neonate larvae of G. lineola frequently feed in rolled-in margins of young leaves of their host plant, Salix viminalis. In addition to nutritional benefits from feeding on young leaves, larvae may also gain protection against adverse weather conditions and general predators by feeding in the leaf rolls. Field and laboratory experiments were conducted to test these hypotheses.

3. Artificial shelters were constructed and cohorts of neonate larvae were placed on experimental plants. In all experiments, larvae preferred to feed in shelters, even when shelters were constructed on mature leaves.

4. In one of the experiments, fewer larvae disappeared when shelters were provided. In a predator exclusion experiment, however, no differences in predator-inflicted mortality on G. lineola were found between shelter-containing shoots and control shoots.

5. A laboratory experiment showed increased protection from desiccation when shelters were present; growth rate was higher for larvae feeding on plants with shelters.

6. Thus, free-living insects may not always be as exposed to environmental hazards as is often assumed. In particular, young larvae may take advantage of preformed structures on their host plant and feed in a concealed microhabitat. Because mortality, in general, is high during early instars, shelter-seeking behaviour may increase survival significantly. The existence of preformed shelters may therefore be a plant characteristic that should be considered when exploring the environmental risks associated with the free-living habit.

Ancillary