Plant chemistry and enemy pressure shape within-stem distribution of the invasive scale Nipponaclerda biwakoensis

We examined whether the crawler-stage of N. biwakoensis scales preferentially settled on the bottom or top sections of P. australis stems, and whether plant nutritional and/or defensive traits shaped this preference. In field surveys, we quantified scale density along the length of individual P. australis stems and found that gravid female scales clustered 3.5 times more often at the stem base than at higher sections. In a greenhouse study, we assayed lower and upper stems of P. australis for carbon, nitrogen, water, and phenolic content, and conducted corresponding laboratory trials to assess scale crawler preferences for stem height.