UV light can guide flies to an Utterly Voracious plant

Good eyesight might attract fruit flies to carnivorous plants, but it can also help flies avoid an untimely death, say Carney and colleagues in a new paper in Bios. “The results of the studies presented here highlight that while olfactory cues are often sufficient to attract fruit flies, visual cues can have a significant impact on the capture process,” said the authors in their paper. “In addition, visual acuity and irradiance levels can impact capture rates by highlighting attractive visual cues, but also perhaps in masking cues that allow fruit flies to avoid capture.”

The paper is the result of a series of undergraduate experiments at Augustana University in South Dakota. Students used Drosophila melanogaster, both as a wild type and a visually-impaired (w¹¹¹⁸) form. Comparing how the two kinds of fly reacted to cues in the experiments revealed what role sight might play in trapping by carnivorous plants. As part of their course students carried out a series of experiments.

The first was relatively simple. Is there a difference in capture rates between fully-sighted and partially-sighted flies? Yes, there was, with the visually impaired flies more likely to be captured. Carney and colleagues said that students had an idea that as the flies had visual problems, they may have been relying on other senses. “The students initially thought that the higher capture rate of the w¹¹¹⁸ flies might be due to an enhanced olfactory sense, compensating for their impaired visual senses. An alternative hypothesis for these results could have been that the WT flies used visual information to avoid the carnivorous plant traps. To examine these two hypotheses, the students exposed the w¹¹¹⁸ and WT flies to artificial traps with and without fruit to determine if the w¹¹¹⁸ flies appeared to have heightened olfactory senses.”

The sniff test failed to distinguish between the fly types, so they looked into more visual experiments.

The next was into irradiance. If the flies were using sight to avoid traps, what happens when you dim the lighting? They found that more light led to fewer deaths for the sighted flies. w¹¹¹⁸ flies, in contrast, were caught at a reasonably constant rate under all light levels.

Next, they looked at the role of ultraviolet patterns, first as funnels, and then as more pitcher-like patterns. They found that UV light alone was not enough to entice flies. The pitcher patterns, with a UV rim, are what highlighted a potential reward to the flies.

The results suggest that eyesight has a role to play in carnivorous plant trapping, but it’s not a simple relationship.

The authors noted that not only have they learned something about fly behaviour, but also about the learning process itself. “These examples of course-based research illustrate how student projects can build upon each other and how the questions arising from one research project can provide the basis for future student projects. Providing student access to previous student projects gives them a powerful tool that helps them design their own projects and creates a more authentic research experience.”