Interaction between willow species and their caterpillar grazers

Abstract

The first aim of this investigation was to determine the effect of leaf removal either by grazing or hand cutting on the photosynthetic ability of the Salix species. The second aim was to investigate any change of leaf quality to feeding insect larvae which occurred as a consequence of the removal. Thirdly, the selectivity of the larvae between different Salix species and its effect on the larval development were studied. The leaf removal by grazing or hand cutting did not decrease the leaf fresh weight in Salix viminalis (submitted to two intensities of treatment) or in S. vitellina, after a period of recovery. The total leaf production in both species was similar to the control. In S. cinerea the grazing reduced the leaf weight and the total leaf production. The leaf size was reduced also. The leaves of previously grazed or hand cut Salix viminalis plants had no depressive effect on the growth of the Geometridae larvae "G". A similar result was obtained with the larvae of the sawfly Amauronematus sagmarius feeding on S. rotundifolia. The Geometridae larvae "G" selected Salix viminalis (58% of the total food consumption) rather than S. cinerea in a choice experiment. S. viminalis promoted a faster growth of the larvae "G" when transferred to it from their previous food plant S. cinerea. The growth of the sawfly larvae was faster on S. fragilis, the species selected by the female for oviposition, than on S. rotundifolia. The death rate of the larvae of Amauronematus sagmarius was higher on both S. viminalis and S. cinerea than on S. vitellina, selected by the adult female for egg laying. Finally, the young leaves of S. rotundifolia promoted a higher death rate in the first generation of Amauronematus sagmarius larvae than the old leaves. The time required for pupation was shorter on the diet of young leaves in the first and second larval generations.