Anastatus furnissi (Hymenoptera: Eupelmidae) as a parasitoid of the bog buckmoth (Lepidoptera: Saturniidae), a rare inhabitant of New York peatlands

The bog buckmoth (Saturniidae: Hemileuca maia) is known only from ten sites around the Great Lakes. Unlike close relatives, it occurs only in peatlands and its larvae feed on Menyanthes trifoliata (Menyanthaceae). Since monitoring began 16 years ago, the New York populations have fluctuated in some fens and disappeared from as many as three. The causes of the fluctuations are unclear. An egg parasitoid, Anastatus furnissi (Eupelmidae), has been proposed as a potentially important source of bog buckmoth mortality. The goal of this project is to assess parasitism rates over the long term and study the oviposition behavior of both host and parasitoid in the field. The host’s oviposition behavior is unusual, in that the moths do not oviposit on Menyanthes but rather on various plants in the vicinity of Menyanthes patches. We recorded the plant species, height, distance from nearest Menyanthes, and size of egg clusters and the attack rate and sex ratios of emerging parasitoids. Plant preference, egg height, distance from Menyanthes, and cluster size differed between sites. At one site, sweet gale (Myricaceae) was the dominant choice while a variety of small shrubs and dead stems were used at the other. Parasitism rates averaged 25-30% in all years and sites regardless of buckmoth population density, suggesting that A. furnissi is a significant mortality source but that parasitism is not density dependent. There were no consistent relationships between parasitism and height of eggs on the plant, egg cluster size, plant species, or sex ratio. At one site, 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. 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, their relative abundance in various peatlands over time, as well as any role played by the parasitoid.