Insect preference drawn from the color wheel

People often make dietary choices based on visual appeal. But this is basic instinct for insects. While insect species may not interpret their surroundings by sight in the same way that humans do, insects do use their eyes to gather information about survival — including visual color cues about what looks good to eat. Aphids, for example, are notorious for feasting on vital crops in agricultural production. Plants that show variations of the color yellow on their leaves are enough to attract the hungry bugs for a communal meal.

The strong attraction that aphids have to the yellow-green portion of the spectrum at around 550 nm was established in the 1950s following the work of Volker Moericke, a professor of applied entomology at the University of Bonn in Germany. His work led to the development of Moericke traps, or yellow-painted pan traps designed to capture and monitor aphids.

Aphids are attracted to certain colors, especially yellow, that can indicate a desirable food source. Courtesy of Jean-Louis Wolff and Sascha M. Kirchner.

The insects can cause significant damage to crops, according to professor Thomas Döring from the University of Bonn’s Institute of Crop Sciences and Resource Conservation. The aphids suck on the plants and remove their nutrients, and they also transmit plant viruses. So it’s in the interest of agricultural health, not to mention crop yield, to figure out how the insects find food sources to satiate their voracious appetites.

Recently, a team of scientists from the University of Bonn and the University of Kassel used spectroscopy to establish a greater understanding of aphids’ response to color by tracking both the aphid’s photoreceptor sensitivity and its behavioral response to plants. The two sets of data were then cross-referenced with a variety of statistical models in a study that was co-authored by Döring and researcher Sascha Kirchner from the University of Kassel’s Department of Agricultural Engineering. The two scientists sought to determine what types of plants most appealed to aphids, to gain insights that will in the future help farmers to protect their livelihoods from the tiny menace.

The team of researchers set more than 200 traps, representing about 70 different colors on the spectrum, at two separate field locations during two consecutive springs — the season when aphids are migrating.

“The colors were mixed in such a way that the entire relevant range of visual perception of aphids (UV to green) was covered and sufficiently varied,” Döring said. “In particular, it was essential that (largely) independent variation was present in different spectral ranges (UV, blue, green, but also yellow and red), so that the potential impact of these ranges could be disentangled.”

Spectral data from the water-filled traps was measured using a RAMSES-ARC spectrophotometer from TriOS GmbH, and the spectra of the upper sides of wheat leaves were measured using an AvaSpec spectrometer from Avantes. Statistical modeling was applied to the results, which showed that aphids were attracted to the color of yellow depending on the levels of nitrogen used to fertilize the leaves. The more intense the nitrogen treatment, the less attracted the insects were. The researchers said that, while further research is needed on more species of aphids, the results so far are food for thought — and for insects.

“The application of, for example, organic mulches in the field have great potential to keep aphids away from the crop,” Döring said. “This effect can most likely be explained by the visual modification (fallow soil is covered by plant material). Our results may help to optimize this promising agricultural practice — and also to make it more widely known.”

The spectral analysis of aphid preferences may help farmers to turn over a new leaf, one that is less attractive to aphid-type pests.