Feasibility of light-trapping in community research on moths: attraction radius of light, completeness of samples, nightly flight times and seasonality of Southeast-Asian hawkmoths (Lepidoptera: Sphingidae)

Abstract

Experimental data and quantitative samples of Sphingid assemblages from tropical Southeast-Asia were analyzed to investigate methodologically relevant topics of light-trapping. MarkRelease-Recapture experiments revealed differences between lepidopteran families in the attraction radius of a light source, but no such differences could be found between 18 species within the family Sphingidae. Attraction radii (for 50% return rate within 5 minutes) were generally below 30 meters, which confirms results from previously published studies. Arrival of Sphingidae individuals at a light source was symmetrically distributed around midnight, and species differed significantly in median arrival time. No evolutionary hypothesis for such flight time differences (such as avoidance of interspecific mating or an effect of body size) could be confirmed from our data. At appropriately chosen sample sites (avoiding dense undergrowth), all-night sampling with a 125 Watt mercuryvapor lamp yielded more than 3⁄4 of the expected species richness of Sphingidae in an average of 5-6 sample nights. Seasonality and temporal changes of local assemblages can probably be neglected for samples from largely non-seasonal regions like Borneo if data stem from a relatively short study time of a few years. In conclusion, (1) there are no indications that light trapping ‘draws’ specimens from distant habitats to the sampling site, (2) we did not find proof that species within the family Sphingidae are differentially drawn to light, which would lead to biases if light-trapping data are used as a measure of relative abundance in the habitat, (3) such biases, on the other hand, probably exist between taxonomically or morphologically more diverse taxa (e.g. for different families), and must be considered for a proper interpretation of results, and (4) light-trapping is an effective means of assessing species composition and relative abundances of Sphingid assemblages in Southeast-Asia, but sampling has to be carried out all night in order to maximize catch size and avoid biases due to different flight times of species.