Bruchid Bettles and Seed Packaging by Palo Verde

Mitchell, Rodger

Cercidium floridum pods usually contain 1 or 2 seeds. If pods contained 3 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 1- or 2-seeded pods rather than 1 large pod. The patterns of mortality from 3 seed predators are: rodents attack all pods equally; all seeds are equally likely to be attacked by Mimosestes amicus (Bruchidae); Stator limbatus (Bruchidae attacks through existing holes cut by M. amicus and the entrances rise almost exponentially with seed count. S. limbatus generally attacks all the seeds of a pod, and selects the larger pods, but pod size varies so much that pods with 2 seeds cannot be discriminated from each other. S. limbatus destroys twice as many seeds in 2- or more seeded pods which confers an advantage on seeds from 1-seeded pods. An egg parasite, Uscana semifumipennis kills approx/= 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 2nd egg to double the survivorship of the 1st egg.

Bruchid Bettles and Seed Packaging by Palo Verde

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