Life history of the imperial moth Eacles imperialis (Drury) (Saturniidae: Ceratocampinae) in New England, USA: distribution, decline, and nutritional ecology of a relictual islandic population

Abstract

The decline and current status of Eacles imperialis (Drury) (Saturniidae: Ceratocampinae) in New England are reviewed, and primary data surrounding the life history and nutritional ecology presented. Though common throughout much of its historical North American range, this species declined precipitously in New England during the 20th century. Suggested explanations for this region-wide decline include the deployment of pesticides and metal halide street lamps and the introduction of parasitoid flies. The existence of a remnant population of E. imperialis, thought to have been extirpated from New England as early as the 1950s, is reported from Martha's Vineyard Island, Dukes County, Massachusetts, U.S.A., representing the last relict of a phenotypically, phenologically, and possibly ecologically infrasubspecific entity. Based on comparisons with museum specimens, adults from this population appear to be indistinguishable from the few historical specimens known from nearby mainland Massachusetts, smaller than those from now extirpated populations in Connecticut, New York, and New Jersey, and slightly larger than members of, the northernmost E. imperialis populations (E. i. pini Michener) found in the Great Lakes region. The Martha's Vineyard population is univoltine, peaking in late July and exhibiting a more contracted flight season than other extant North American populations. Both parentage and food plant significantly affect larval growth and development, and although larvae on Martha's Vineyard feed extensively if not exclusively on pitch pine (Pinus rigida) in the wild, they grow significantly faster, attain greater pupal weights, and more efficiently convert ingested and digested tissues of post oak (Quercus stellata) to biomass in the laboratory. Performance as measured by relative growth rate and the efficiency of conversion of ingested and digested food to biomass (ECI and ECD) are correlated with foliar nitrogen and water content: post oak foliage during the larval growth season contains more nitrogen and water than corresponding amounts of pitch pine foliage growing in the same soils. It is suggested that there exists a non-nutritional explanation for the association of E. imperialis with pitch pine and for its pattern of decline and persistence. The taxonomic and possible biogeographic affinities of this population are discussed from within the context of a growing understanding of New England's diverse yet threatened lepidopteran fauna, and the potential for reintroducing E. imperialis to mainland New England is discussed.