Diurnal Activity Patterns of Flower Flies (Diptera: Syrphidae) in an Illinois Sand Area

Abstract

The temporal and spatial distribution patterns of the syrphids Ceriana abbreviata (Loew), Mallota bautias (Walker), M. posticata (F.), Somula decora Macquart, Sphiximorpha signifera (Loew), and Spilomyia hamifera Loew were examined in an Illinois sand area. In the morning, adults congregated in fields near flowering Cornus drummondi Meyer, C. racemosa Lam., and Sambucus canadensis L. where food and mates were plentiful. Around midday, as food availability declined and hygrothermal stress increased in open areas, the syrphids entered an oak-hickory forest where hygrothermal conditions were more favorable. In the afternoon, females of M. posticata and S. decora oviposited in rot cavities in trees, and males defended mating territories around these larval habitats. Adults of M. posticata performed the same behaviors at artificial oviposition sites that were placed in the forest understory. On days when the temperature in the forest exceeded 29°C, the activity curve of both sexes of M. posticata changed from unimodal to bimodal, the afternoon lull corresponding to the hottest part of the day. The overall behavior of these 6 syrphids may have been selected in response to food availability, hygrothermal stress, and mating success.