LOCAL ADAPTATION IN THE ARMORED SCALE INSECT PSEUDAULACASPIS-PENTAGONA (HOMOPTERA, DIASPIDIDAE)

We investigated adaptation of the armored scale insect Pseudaulacaspis pentagona (Targioni-Tozzetti) to individual mulberry trees (Morus alba L.) in Maryland, USA. We tested local adaptation by transferring eggs within and between trees and by measuring the subsequent survival of developing scales. Survival of P. pentagona was significantly higher when raised on their natal host tree compared to rearings on novel trees. This finding is consistent with local adaptation of scale populations to individual host trees. However, we found evidence for differences in local adaptation of scale populations only between populations on distantly separated mulberry trees. There was no evidence for genetic differentiation of scale populations on neighboring trees, suggesting that gene flow inhibited local adaptation. By adapting to individual plants, few populations of herbivores appear to sacrifice their ability to colonize new conspecific hosts. While local adaptation may fine tune herbivore populations to individual host phenotypes, it is unlikely to play a general role in explaining the patchy distribution of herbivorous insects on their host plants.