Small-scale variation in sexual size dimorphism and sex ratio in the aquatic moth Acentria ephemerella Denis and Schiffermüller, 1775 (Lepidoptera: Crambidae)
Résumé
The aquatic herbivorous and capital-breeding moth Acentria ephemerella Denis and
Schifferm€uller, 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 G€uttingen 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 G€uttingen. 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.