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.
