The natural history of the parasitic wasp Trogus pennator (Hymenoptera: Ichneumonidae): Host‐finding behaviour and a possible host countermeasure

Abstract

The parasitic wasp Trogus pennator (Ichneumonidae) attacks the larvae of swallowtail butterflies (Papilionidae). Female T. pennator were followed in the field as they searched for larvae of the zebra swallowtail butterfly, Eurytides marcellus (Papilionidae), feeding on Asimina (Annonaceae) in central Florida, USA. Predictions of host‐finding theory and interactions with the host were thus investigated in a natural setting. Wasps seldom flew to plants other than Asimina and apparently recognized the plants by visual cues. Plants were attractive regardless of host presence, as the wasps approached plants lacking E. marcellus feeding damage twice as often as they approached damaged plants. However, wasps approached damaged plants at a rate greater than their frequency in the Asimina population, indicating that they can detect host damage before they approach the plants. After approaching within 0.5 m of plants, wasps tended not to land on plants lacking feeding damage. A comparison of the plants they landed on, however, showed no consistent preferences for damaged plants. The weaker trends in the latter data indicate that the presence of feeding damage was not the sole criterion for landing, although it evidently influenced behaviour. After landing, wasps spent more time searching damaged plants than undamaged plants. Butterflies preferred to oviposit on plants shorter than those searched by T. pennator. Possible adaptive consequences of this phenomenon are discussed.

Keywords:

• Field observations
• host‐finding behaviour
• Ichneumonidae
• Papilionidae
• parasitic wasp

Acknowledgements

Special thanks are due to H. Damman, for suggesting the Lake Delancy field site, and to J. Clutts and the staff of the Lake George Ranger District (Silver Springs, Florida) for permitting work in the Ocala National Forest. J. Brooks, A. Brower, J. Carpenter, T. Carr, P. Feeny, M. Haribal, C. Heinz, M. McDonald, S. Murphy, H. Nadel, M. Sharkey, M. and C. Tauber, and B. Traw helped with field work and manuscript preparation. This project was funded by National Science Foundation Research Grants IBN‐9119674 and IBN‐9420319 to Paul Feeny and IBN‐9600094 to K. Sime and P. Feeny, and by grants from the Rawlins Fund (Department of Entomology, Cornell University), the Cornell Graduate School and the Andrew Mellon Foundation to K. Sime. The author was also supported by a Liberty Hyde Bailey Fellowship (Cornell University) and a National Science Foundation Graduate Research Fellowship.