Bruchid Bettles and Seed Packaging by Palo Verde

Cercidium floridum pods usually contain one or two seeds. If pods contained three or more seeds, pod biomass would be reduced by 19% and that energy could be diverted into seeds. Intrinsic factors do not explain the wasteful packaging; interactions at a node divert energy into several one— or two—seeded ponds rather than one large pod. The patterns of mortality from three seed predators are: (1) Rodents attack all pods equally; (2) All seeds are equally likely to be attacked by Mimosestes amicus (Bruchidae); (3) Stator limbatus (Bruchidae) attacks through exit holes cut by M. amicus and the entrances rise almost exponentially with seed count. Stator limbatus generally attacks all the seeds of a pod, and selects the larger pods, but pod size varies so much that pods with two seeds cannot be discriminated from each other. Stator limbatus destroys twice as many seeds in two— or more seeded pods which confers an advantage on seeds from one—seeded pods. An egg parasite, Uscana semifumipennis kills °40% of the eggs of both beetles. This mortality, plus a nearly 40°% loss to heat and desiccation, makes it advantageous for M. amicus to put one egg on top of another, thus sacrificing a second egg to double the survivorship of the first egg.