Effects of herbivory and inflorescence size on insect visitation to Eryngium yuccifolium (Apiaceae) a prairie plant

Herbivory and inflorescence size can influence floral visitors. Damaged inflorescences have been shown to have fewer floral visitors due to changes in floral appearance/chemistry, whereas larger inflorescences attract more pollinators because of greater pollen/nectar reward. This study examined whether floral herbivory by a moth, Coleotechnites eryngiella Bottimer (Gelechiidae), and inflorescence size have any effect on the attractiveness of Eryngium yuccifolium Michaux (Apiaceae) to floral visitors. In particular, the study seeks to determine how combined effects of inflorescence size and herbivory affect overall and main composition of floral visitors groups. Twelve plants, six with one inflorescence stalk (three with and three without herbivory) and six with three inflorescence stalks (three with and three without herbivory) were observed for floral visitors in 2004 and 2007 at four remnant tallgrass prairies located in east-central Illinois, USA. Damaged inflorescences had lower flower visitation than undamaged inflorescences. Larger floral displays attracted more floral visitors. Differences between the numbers of flies, bees and beetles visiting the flowers were not independent of herbivory and inflorescence size. This study provides additional evidence that herbivory and inflorescence size can influence insect visitation. In addition, this study provides further support to recent publications regarding the more sophisticated nature of the pollinator guild associated with members of Apiaceae. Finally, it also provides the foundation for future studies to determine how differences in the composition of floral visitors are associated with the male and female inflorescence phases of E. yuccifolium and their relation to male and female fitness.