Escape of Cassia Grandis L. Beans From Predators in Time and Space

Abstract

In Central American deciduous forests, most of the seeds of the caesalpinaceous legume tree Cassia grandis are killed by the larvae of two bruchid beetles, Pygiopachymerus lineola and Zabrotes interstitialis. Pygiopachymerus lineola oviposits on the large pods, the first—instar larvae bore into the seeds, and the emerging adults cut large exit holes in the pod wall. Moth larvae gain access through these holes and eat clean much of the sticky pulp around the seeds. Simultaneously, the adults of Z. interstitialis enter through the P. lineola exit holes and oviposit directly on all clean seeds. In heavily disturbed communities where vertebrate dispersal agents are absent, these host—specific bruchids achieve almost 100% predation on the C. grandis seed crop; however, the more rapidly the dispersal agents remove the seed pods, the less seed predation there will be by Z. interstitialis. Since C. grandis bears mature fruit every other year, the size of each seed crop is large enough to surpass the predation abilities of the bruchids that survive the distance in time and space between seed crops. The system may be viewed as an example of predator satiation. The potential for further co—evolution of the bruchid—Cassia interaction is high, but numerous opposing forces in the selective process can be identified.