Nectar plant preferences and pollen loads in Hemaris moths: Diet analysis of pollen collected from individuals

Background/Question/Methods

The majority of nectar feeding moths in the family Sphingidae are nocturnal, but four North American species are diurnal. Three species – Hemaris thysbe, H. diffinis, and H. gracilis – occur in the Eastern United States, and are commonly known as hummingbird moths or clearwing moths. These Hemaris species mimic species of Bombus in appearance and size, and mimic both Bombus and hummingbirds by foraging for nectar during the daytime. Previously, we have shown that despite these similarities, Hemaris do not forage for nectar in the same manner as the species they mimic; rather they demonstrate foraging similarities to the nocturnal sphingids from which they evolved. Nocturnal Sphingidae demonstrate preferences for flowers that are white or light colored and fragrant – such traits that make a floral nectar resource easily detected at night. We tested whether floral nectar resource preferences exist in Hemaris diffinis and H. thysbe.

 

From May - July 2010, we netted Hemaris moths foraging at Monarda fistulosa, Petunia x hybrida, Kalmia latifolia, Verbena bonariensis and Syringa vulgaris. We swabbed them with fuchsin-stained gelatin to collect pollen from their bodies and analyzed this pollen via light microscopy, identifying grains to species, genus or family. We asked the following questions: (1) Given the nectar resources available in the system, what percentage of nectar resource species is visited by Hemaris? (2) What, if any, shared morphological traits unite flowers visited by Hemaris? (3) Are there differences in the number of species of pollen carried by moths within or among the Hemaris genus? 

Results/Conclusions

Of the 51 Hemaris moths swabbed all individuals had pollen present on their bodies. Hemaris thysbe typically carry on average 3 species of pollen on their bodies while all collected individual Hemaris diffinis carried only one species. This represented visitation to roughly 1/4 of available nectar resources by H. thysbe and 1/12 of available nectar resources by H. diffinis. Flowers visited by Hemaris represent a broad array of morphologies. Hemaris do not demonstrate a preference for any specific floral morphological traits, indicating that they represent a more generalized guild of pollinators than their nocturnal relatives.