Black Pineleaf Scale (Homoptera: Diaspididae) Population Density in Relation to Interdemic Mating

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Abstract
Density of black pineleaf scale, Nuculaspis californica (Coleman), insects populating ponderosa pine varies with distances separating sampled twigs from foliage of adjacent infested trees. Scale densities on needles touching or resting within 10 cm of needles from a neighboring infested tree were significantly lower and more variable than densities on more distant twigs from the same pine. This result is consistent with the hypothesis that interdemic mating between scale insects adapted to the defensive pattern of different individual host trees introduces locally maladaptive traits. Both reductions in scale density and sex ratio patterns reported previously suggest an outbreeding depression resulting from this interdemic gene flow.