EUCOSMA GIGANTEANA (RILEY) AND SILPHIUM PERFOLIATUM L., MORPHOLOGICAL VARIATION IN AN INSECT-PLANT ASSOCIATION IN EASTERN SOUTH DAKOTA.

Silphium perfoliatum L., cup plant, has potential as a new multi-purpose crop. It is pollinator-friendly and has biodiversity enhancement, conservation, economic, and medical potential. In eastern South Dakota, S. perfoliatum can produce more than 20 Mg (million grams) ha-1 of biomass and 0.09 Mg ha-1 of seed in agronomic plantings. The giant eucosma moth, Eucosma giganteana (Riley), is a major pest of agronomic S. perfoliatum in the region. We provide a summary of this insect and its association with its host. Our experimental objectives were to determine if the frequency of rhizome occupation by late instar larvae and if their final prepupal size were influenced by plant genetic or environmental effects. In October 2009, several individual plants from each of 32 half-sib families were removed from the field. Rhizomes, proaxes, and shoots were examined for the presence of larvae. Each larva was counted and measured for total length, width, thoracic tergite length, head length, and head width. Significant differences were found among half-sib families and between locations for frequency of shoot infestation, degree of crown and rhizome feeding, number of larvae per shoot, and larval morphometrics. The parasitoid Bracon cf. mellitor Say (Hymenoptera: Braconidae) was found parasitizing larvae feeding in floral meristems, but no parasitism was found in larvae in the crown or rhizomes. [ABSTRACT FROM AUTHOR]