Green peach aphid (GPA – Myzus persicae) is a widespread pest species attacking many broadacre and horticultural crops.
Despite the name, GPA are not always green in colour, ranging from shades of light and dark green, yellow, pink, red and even black.
Each colour-type is called a ‘morph’ and this colour variation is largely due to the type of carotenoids (colour pigments) in the aphid.
There is speculation that greater levels of insecticide resistance are present in red morph populations of GPA. However, this is not supported by any studies.
At cesar, we culture populations of GPA for use in insecticide-resistance experiments.
These populations have been collected from different horticultural and grains crops all over Australia, and many of these populations contain multiple coloured aphids including light and dark green, red, and black morphs.
During both our laboratory and field experiments, we have shown that different colour morphs from a single population respond in exactly the same way to insecticides.
In particular, we have found that the dose response curves of both red and green morphs of insecticide susceptible GPA are identical, indicating that factors other than aphid colour are the source of insecticide resistance in this species.
So why do the red GPA seem to survive spraying?
- A resistant population of GPA (that happens to contain red morphs) is present in your crop
- The red morph is much more obvious (both larger and more distinct) than the green morph on plant leaves