There are few events in nature that are more predictable than the emergence of periodical cicadas. The insects emerge from the ground after 13 or 17 years (depending on brood and species) of development. Karlin et al., (1991) biochemically examined over 750 Magicicada tredecassini belonging to Brood XIX which emerged during the spring of 1985. In this study they found evidence for rapid deterioration of heterozygosity for two esterase loci,Gi-3-pdh and Gpi, and suggested that this deterioration may be related to differential mating classes. To test this hypothesis, we re-sampled from this same brood at the same location during fall (1993) and winter (1994), nine years into the 13 year development of this brood. The current biochemical data suggest no significant deviations from Hardy-Weinberg expectations for either Est-3, Gl-3- pdh or Pgm-1, but in several cases Est-1 or Est-2 displayed significant departures. Our failure to find excess heterozygosity in the nymphal sample is interpreted to support weakly the size-mediated mating system hypothesis.

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