Relationships between the lengths of floral tubes and moth mouthparts: implications for flower preferences of nocturnal moths

Abstract

Morphological trait matching between flowers and the mouthparts of their visitors is important for the ecology and evolution of plant–pollinator interactions. Although both nocturnal and diurnal floral visitors are important pollinators, nocturnal visitors such as moths (Lepidoptera) remain less well studied. To elucidate the relationship between floral tube length and mouthpart length in nocturnal floral visitors, we examined moths visiting the flowers of 34 plant species (26 families) in Hyogo, Japan. A total of 970 adult moths representing 245 species (14 families) were observed. Hawkmoths (Sphingidae) and settling moths (mainly Crambidae, Noctuidae, and Geometridae) accounted for 4.0% and 96.0% of all individuals, and 3.3% and 96.7% of all species, respectively. Hawkmoths had longer proboscises (mouthparts/tongues) than settling moths. The relative proportions of hawkmoths and settling moths increased and decreased, respectively, with increasing floral tube length. Mean, minimum, and maximum proboscis lengths of all moths (hawkmoths and settling moths combined) were positively correlated with floral tube length. Among hawkmoths, maximum proboscis length was positively correlated with floral tube length, indicating that long-tongued hawkmoths avoid visiting short-tubed or nectar-exposed flowers. Among settling moths, minimum proboscis length was positively correlated with floral tube length, indicating that short-tongued settling moths avoid visiting long-tubed flowers. Consequently, long-tongued moths (hawkmoths) prefer to visit long-tubed flowers, whereas short-tongued moths (settling moths) prefer to visit short-tubed or nectar-exposed flowers.