Why There are So Few Species of Aphids, Especially in the Tropics

Abstract
It is possible to account for the distribution and low species diversity of aphids in terms of the constraints imposed by their way of life, namely, the short period for which they can survive without food, their high degree of host specificity, and the low efficiency with which they locate host plants. Ninety percent of plants are not used as hosts by aphids (Eastop 1973) mostly because these plants are just too rare.