Performance of the native Tyria jacobaeae L. (Lepidoptera, Erebidae) on native and invasive ragwort species in Germany

Abstract

The occurrence of the native ragwort Jacobaea vulgaris and its relatives is a problem for grassland owners, due to the pyrrolizidine alkaloids being poisonous for livestock. Besides J. vulgaris, the invasive Senecio inaequidens is challenging and control measures in line with nature conservation goals are needed. To evaluate prospects of using the native and herbivorous Tyria jacobaeae as a biological control agent, we studied its performance on S. inaequidens in comparison to the native J. vulgaris and J. aquatica. We compared the egg-laying decision of 106 females (number and placement of eggs on the plant, in the surrounding or not laid at all) and performance of 50 larvae, reared in five treatments with different food supply (only leaves or leaves and flowers) of the three ragwort species. We found that females oviposited preferably on the plant when J. vulgaris and J. aquatica were available, whereas in the presence of S. inaequidens most eggs were retained and not laid. No differences were observed in larval weight, weight gain, or leaf area consumed when larvae were fed with J. vulgaris (leaves, leaves and flowers) or J. aquatica leaves. Furthermore, 90% of the larvae provided with these treatments pupated successfully. In contrast, larvae developed slowly when provided with S. inaequidens and none survived to pupation. Our results show that J. aquatica is a suitable alternative host for T. jacobaeae, whereas S. inaequidens is not. We therefore argue that T. jacobaeae has no biological control potential against S. inaequidens.