Seed destruction of California morning glories (Convolvulaceae: Calystegia) by bruchid beetles [Megacerus impiger]

The bruchid (seed) beetle Megacerus impiger is usually found in populations of perennial, native morning glory (Calystegia) in California. Each beetle matures inside a single Calystegia seed, destroying the seed. Seed set of the four ovules per flower prior to predation by the beetles varies among the populations sampled from 1.6 to 3.8. Mean seed weight varies also, from 32.8 mg/seed in C. atriplicifolia to 11.2 mg/seed in C. stebbinsii but beetles can develop to adults in all. Beetles lay eggs on young seeds in May or June in most Calystegia populations in cismontane California. Adults emerge from mature seeds by July or August and oviposit on other mature seeds retained in open capsules. The second crop of adults produces a third ovipositing or overwintering group of beetles; there is thus a potential for extensive seed destruction in the plants. Minimum seed destruction (in C. fulcrata) varied from 0.005 percent to 36.3 percent, not considering predation on fallen seeds. Genus-specific seed predation by M. impiger among at least 13 taxa of Calystegia in California suggests close similarities in reproductive features of a group in which taxa have been difficult to distinguish by reproductive features alone.