Food plant quality of Cynoglossum officinale and herbivory by Ethmia bipunctella (Lepidoptera, Ethmiidae)

The oligophagous lepidopteran Ethmia bipunctella F. (Lepidoptera: Ethmiidae) occurs in low numbers in Meijendel, the Netherlands, in spite of the great abundance of its host plant Cynoglossum officinale L. In this study, we examine the importance of food plant quality on individual performance of E. bipunctella , and discuss the impact on its population density. Grazing by E. bipunctella reduced the growth of plants in a growth room. In the field, flowering plants rather than rosettes were chosen for oviposition. In a choice experiment, larvae preferred undamaged rather than damaged leaves, suggesting that herbivory causes a rapid fall in plant acceptability. However, the larvae grew equally well on damaged and undamaged leaves. Our observations imply a role for alkaloids: flowering plants have a much lower alkaloid content than rosettes; and plants with eggs in the field had a lower alkaloid content than plants without eggs.