Department of Physics, Chemistry and Biology (IFM)

As a group, Trichoptera were strongly attracted to light but not all species were equally attracted to light. Why are some species more attracted to light than others? For one thing, there are several ways for organisms to navigate: aerodynamic, gravitational, chemical, geomagnetic, acoustic and imaging cues are all ways of guidance that compete with light. More active species are more likely to pass a light source while larger species usually have larger eyes which perceive light sources better. My analysis indicated that day-active species were less attracted to light than night-active species, but they did not differ from evening-active. However, being a day-active species did not necessarily mean they avoided a light trap. Other studies doing laboratory experiments have shown that the method of light trapping could create an artificial product of higher flight activity at night even for day-active species. There could be many ecological explanations and more studies are needed to further investigate what causes different responses to light in the order Trichoptera.

It is known that the sex ratio in Trichoptera is not equal and that the ratio varies with species. My analysis found more females than males in absolute numbers, especially in light traps, and there seems to be more species of Trichoptera with females being attracted to light. That females are found in greater numbers could have three reasons: they are more attracted to light, have a higher flight activity or that the natural female-to-male ratio of adults is higher. The ecological reasons for differences between sexes are several and needs to be further examined. No single reason seemed to explain the variation between species, although size dimorphism was a likely candidate.

There was some evidence that light traps would be more efficient during longer nights, however the results were not conclusive.