Small-scale variation in sexual size dimorphism and sex ratio in the aquatic moth Acentria ephemerella Denis and Schiffermüller, 1775 (Lepidoptera: Crambidae)

Abstract

The aquatic herbivorous and capital-breeding moth Acentria ephemerella Denis and Schiffermüller, 1775 feeds on submerged pondweeds, Potamogeton spp., and is highly preyed upon by fish in the littoral zone. We studied the spatiotemporal within-lake variability of length, sexual size dimorphism (SSD) and sex ratio of A. ephemerella pupae and of larval population densities. Population densities at three sampling sites strongly increased from July to August and were significantly higher at the Reichenau site in July. Acentria ephemerella sex ratio was male-biased at the Güttingen and Hagnau sites, but showed unbiased or slightly biased sex ratios at Reichenau. The SSD was strongly female-biased. Female size and SSD declined during summer, possibly due to reduced food quantity/quality. The SSD was highest at Reichenau, with little to no differences between Hagnau and Güttingen. At Reichenau, the high population size in July coincided with an unbiased sex ratio, and large SSD/female size due to multiple, possibly interacting factors, including fish predation.