Experimental evidence for male biased flight-to-light behavior in two moth species

Many studies report a greater abundance of male than female moths in light trap catches. The finding was interpreted as evidence for male-biased attraction to light, but alternatives could not be ruled out. For example, it is not known, how much the sex ratio in the catches deviates from the natural sex ratio. To overcome these limitations, we experimentally tested the flight-to-light behavior of two moth species, Yponomeuta cagnagella (Hubner) (Lepidoptera: Yponomeutidae) and Ligdia adustata (Denis and Schiffermuller) (Lepidoptera: Geometridae), under standardized conditions in an enclosed environment. In our test, we controlled the sex ratio, age, and population size. We recorded the moths caught in the trap and those that remained outside. Depending on the species, between 27 and 72% of all moths were caught in the light trap. We found that male moths were significantly and about 1.6 times more frequently attracted to the light than female moths. Our results were consistent for both species and hold good on the level of populations. We experimentally supported the general observation of a sexual dimorphism in the flight-to-light behavior of moths. Possible functional explanations include different flight activities of males and females or differences in the perception of light between males and females. Our experimental demonstration of a sexual dimorphism in the flight-to-light behavior of moths together with the common observation of an overrepresentation of males in light traps and other artificial light sources has implications for population and conservation biology.