“Oops! Something tells me that my camouflage isn’t as effective as it used to be!” Source: cuttspoetrycorner.blogspot.com, http://www.iconspng.com & Shelly, lh5.ggpht.com, montage: laidbackgardener.com
Some gardeners claim that red- or purple-leaved vegetables are more resistant to insect attack than green ones. Red cabbages, purple kales, purple beets, etc. are, in their experience, less often affected by some insects, including caterpillars and aphids.
Perhaps this is because the odd coloration of the foliage makes the insect’s natural camouflage less effective?
Does the mother insect, usually pale in color, feel more exposed when she lands on a purple leaf and so moves to a greener plant where she feels more at ease? Or maybe she lands just as easily on a dark-leaved plant despite its color, but its predators notice it faster on purple foliage and eat it, ending the infestation before it even starts? Or see its white eggs or pale green larvae more easily and consume them before they do any harm?
One thing is certain: humans can more easily spot pale-colored insects and eggs on purple or red foliage and so can react faster by manually harvesting the intruder or treating with a pesticide. For example, a cabbage looper caterpillar, with its pale green color, is perfectly camouflaged on a green leaf and therefore almost invisible, but stands out like a beacon when it’s on a purple leaf.
It would be interesting for someone to do a study to see if it’s true that purple and red vegetables are initially less attractive to insects. It sounds to me like it might be a simple yet interesting summer project for students interested in horticulture!