Autumn leaves seen through herbivore eyes

Abstract

Why leaves of some trees turn red in autumn has puzzled biologists for decades, as just before leaf fall the pigments causing red coloration are newly synthesized. One idea to explain this apparently untimely investment is that red colour signals the tree's quality to herbivorous insects, particularly aphids. However, it is unclear whether red leaves are indeed less attractive to aphids than green leaves. Because aphids lack a red photoreceptor, it was conjectured that red leaves could even be indiscernable from green ones for these insects. Here we show, however, that the colour of autumnal tree leaves that appear red to humans are on average much less attractive to aphids than green leaves, whereas yellow leaves are much more attractive. We conclude that, while active avoidance of red leaves by aphids is unlikely, red coloration in autumn could still be a signal of the tree's quality, or alternatively serve to mask the over-attractive yellow that is unveiled when the green chlorophyll is recovered from senescing leaves. Our study shows that in sensory ecology, receiver physiology alone is not sufficient to reveal the whole picture. Instead, the combined analysis of behaviour and a large set of natural stimuli unexpectedly shows that animals lacking a red photoreceptor may be able to differentiate between red and green leaves.

The virulence–transmission trade-off in vector-borne plant viruses: a review of (non-)existing studies

“…Interestingly, enhanced plant penetration by aphid stylets was observed on symptomatic virus-infected plants compared with healthy plants (Alvarez et al 2007). Moreover, it has long been known that aphids are significantly attracted by yellow (Doring et al 2009) and that some plant viruses induce symptoms resulting in chlorosis, mosaics or other modifications that lead to yellowing of the leaves. Aphids have been shown to prefer to land and settle on virus-infected plants with yellowing leaves, possibly owing to the fact that insect vectors use visual cues to choose suitable plants (Fereres et al 1999;Hodge & Powell 2008).…”

Visual Cues and Host-Plant Preference of the Bird Cherry-Oat Aphid,Rhopalosiphum padi(Hemiptera: Aphididae)

“…For example, Hyalopterus pruni (Geoffroy) was attracted to unsaturated tints of orange-yellow-green with an optimum at yellow, whereas Aphis fabae (Scopoli) was more attracted to saturated tints that correspond to their respective host plants Phragmites communis (Poaceae) and Beta vulgaris (Chenopo-diaceae) (Moericke 1969). Furthermore, Rhopalosiphum padi (L.) was found to be attracted to green leaves of its primary host plant in autumn instead of trees with yellow leaves as predicted by the autumn co-evolution theory and the aphid colour preference model (Archetti & Leather 2005;Döring et al 2009). These findings could be relevant for aphid control on agricultural crops.…”

“…To address this problem, Döring et al (2009) developed a colour choice model based on testing 70 different colours in the field, tentatively taking both aphid and human photoreceptor characteristics into account. The model indicated that aphids are able to distinguish between red and green leaves, with a tendency to avoid red.…”

Effect of flower traits and hosts on the abundance of parasitoids in perennial multiple species wildflower strips sown within oilseed rape (Brassica napus) crops

“…This result is consistent with that obtained by Jönsson (2005), who also found that yellow is a strong visual cue for pollen beetle parasitoids. The attraction to yellow is caused by the positive input from green receptors coupled with a negative input from blue receptors in the insect eye, termed the 'green-blue colour opponent mechanism' (Döring et al 2009;Döring et al 2012). In contrast to Meligethes spp.…”