Why Are Seeds of the Central American Guanacaste Tree, Enterolobium cyclocarpum, I Not Attacked by Bruchids2 Except in Panama

Abstract

The ranges of most other bruchids are usually contiguous with their hosts, but Stator generalis (Coleoptera: Bruchidae) is known to feed only in exposed seeds of guanacaste, Enterolobiurn cyclocarpurn (Leguminosae: Mimosoideae),in a restricted area of central Panama. Because this tree is widespread in the neotropics and yet is not preyed upon by seed beetles throughout the rest of its range, we fed seeds from Mexico, Guatemala, EI Salvador, Honduras, and Costa Rica, and from other areas of Panama, to S. generalis. They were able to develop normally in all these seeds; thus, we rejected the hypothesis that seeds from central Panama were chemically unique. We hypothesize that S. generalis has not spread northward, because guanacaste seeds are not available in amounts or a pattern appropriate for S. generalis to survive. This is because cattle and horses eat nearly all the fruits, thereby widely scattering the cleaned seeds. Small rodents which have access to horse and cattle dung remove the seeds even farther from a state accessible to bruchids. Further, variability in the number of seeds set and available in a specific locality may also reduce the pool of bruchids available for emigration and raise the chance for local extinction. Probably a pool of fruit-free seeds exposed on the surface of the ground only accumulates in sufficient quantity to maintain a population of S. generalis in localities such as city parks, gardens, corrals, and other areas where there is considerable human traffic. The possible effects of Pleistocene large mammals on this system are also discussed.