PS 45-6
Oviposition patterns and parasitism of the bog buckmoth, a rare inhabitant of New York peatlands
The bog buckmoth is known only from ten peatlands around the Great Lakes. Since monitoring began 15 years ago, the New York populations have undergone fluctuations, declined in some fens, and disappeared from one. The ecological factors that affect bog buckmoth populations have not been studied. One factor may be its unusual oviposition behavior. Unlike close relatives, the bog buckmoth occurs only in peatlands and the larvae feed on Menyanthes trifoliata. However, the moths do not oviposit on Menyanthes because their eggs are the overwintering stage and Menyanthes dies back during the winter. Instead, they place their eggs on various plants that are not food for the larvae. It is rare for moths to lay eggs near, rather than on, the food plant, and for young larvae to travel to find food. Another possible factor is an egg parasitoid, Anastatus furnissi. Our goals were to characterize the oviposition preferences of bog buckmoth as related to plant choice and microhabitat preference and to examine the extent of parasitism. Vegetation was surveyed to establish species abundance and density. For egg clusters, we recorded the oviposition plant, the height of egg clusters on the plant, distance from nearest Menyanthes, cluster size, and parasitism.
Results/Conclusions
Eggs were found on a variety of plants at the two field sites we investigated. Plant identity, egg height, distance from Menyanthes, and cluster size differed between the two sites. The selection of plant species was not random. At one site, Sweet Gale (Myrica gale) was the dominant choice while dead stems of sedges and ferns were used most often at the other. Parasitism rates averaged around 30%, suggesting that A. furnissi is a significant mortality source. Parasitized egg clusters were significantly closer to Menyanthes than were unparasitized eggs, suggesting a trade-off between susceptibility to parasitoids and distance to food plant. There were no relationships between parasitism and height of eggs on plant, egg cluster size, or plant species. As the suitability of habitats for the bog buckmoth depends on the ability of the caterpillars to find food, these data may help explain the distribution of these insects as well as their relative abundance in various peatlands over time.