Discuss If a plant-homopteran-ant interaction has a net negative effect on the individual plants occupied by the homopteran (see fig 12.24), why are these plants not selectively eliminated from the population? Ants protect the scale insects from predators and parasitoids in exchange for nutrients secreted by the scale insects. Ants present Ants removed 6 Ants present Ants removed 5 6 – 5 – No. of scales parasitized No. of scales dead from other causes N 3 2 2 41 41 8 15 29 Days after removal (a) Parasitized scales. Copyrigo Poncion, 8 15 29 Days after removal (b) Scales dead from other causes.