The effect of the water-lily beetle, Galerucella nymphaeae, on leaf production and leaf longevity of the yellow water-lily, Nuphar lutea

Abstract

SUMMARY. 1. The effect of the water-lily beetle, Galerucella (=Pyrrhalta) nymphaeae (L.), (Coleoptera, Chrysomelidae), on the leaf production and leaf longevity of the yellow water-lily, Nuphar lutea (=N. luteum) (L.) Sibth. & Sm., was studied experimentally in southern Finland during one growth season. 2. Twelve cages, each containing a single rosette of the water-lily, were established in the lake during May. Two treatments were randomly applied to cages: (i) control (herbivory not allowed), and (ii) fifty beetles added at the beginning of the season. Leaves were marked individually and the production of new leaves was followed until October. 3. In both treatments the production of floating leaves continued until the end of August but declined towards the end of summer. Herbivory did not affect the number of leaves produced, i.e. the plants did not compensate for the loss of leaves. 4. Leaf longevity was reduced dramatically (up to —60%) when herbivores were present. Leaves that emerged during the most intense period of larval growth had a life-span one-third of that of the control group.