Aphids living in a completely closed gall, or nest, use the plant walls to dispose of their waste, reports a study in Nature Communications this week. This explains how the aphids are able to live isolated from the outside world for several months, and sheds light on how they have evolved to use their host plants for nest cleaning.
Insects, such as aphids, form growths known as galls on their host plant that function as both a home and a food source for the insects. These galls most often have an opening, which makes foraging, defense and waste disposal simple. However, some social aphid colonies - made up of hundreds to thousands of individuals - form completely closed galls, presenting a problem for disposing of their waste product - honey dew - that collects inside the gall. Takema Fukatsu and colleagues studied and compared different aphid species that formed open and closed galls. They discovered that for the aphids living in closed galls the inner surface of the gall is specialised for absorbing water. This therefore removes the honeydew waste via the plant vascular system, solving the problem of having no obvious waste disposal exit.