Young, B.L., Johnson, R.H., & Alstad, D.N. 1993 Sex-ratio variation in scale insects on ponderosa pine: effects of needle age class.. Bulletin of the Ecological Society of America 74 (2 suppl.): 497.

Notes: [Proceedings of 1993 Annual Meeting of the Ecological Society of America: Ecology and Global Sustainability, held July 31-August 4, 1993 in Madison, Wisconsin.] Sex-ratios in the univoltine scale insect, Nuculaspis californica on Pinus ponderosa are female-biased; however, significant variation occurs among needle year classes on an individual tree. Although newer needles have higher scale densities, proportionally more males are found on older needles. This could result from 1) differential male survival on older vs. newer needles, 2) shorter dispersal distances by male vs. female crawlers and/or 3) variation in clutch sex ratio among females on needles of different age. Clutch samples collected throughout the summer showed that females on older needles had proportionally more male offspring. In a controlled manipulation, female scales were eliminated from all but a single needle year class and the dispersal of their male and female progeny was quantified. Female crawlers moved greater distances and their movement was biased toward newer needles; males remained nearer to their natal position. These findings are consistent with the hypothesis that females seek nutritionally rich needles while males remain on nutritionally inferior needles damaged by their mothers' feeding. Keywords: males.