Seasonal abundance and temporal variation in dispersion patterns of the poplar petiolegall aphid,Pemphigus populitransversusRiley, were examined in serial planting studies of cabbage and broccoli from 1986 to 1988 using variance/mean ratioS2/$\bar x$, Green'sCx, Standardized Morisita'sIp, and Taylor's regression of log variance on log mean. All indices predicted an aggregated dispersion of aphid numbers, with no apparent trends in seasonal variation in dispersion. Values ofβfrom Taylor's regression were homogeneous among cultivars and plantings in 1986–1987, but the slope calculated for aphid dispersion in the September planting differed from theβvalues estimated in October and December plantings in 1987–1988. The estimatedβcalculated from the commercial cabbage field was not different from most of the serial plantings. Alate fundatrigenia began emerging from laboratory-held galls in early July, and peak emergence occurred from October through November. There was a corresponding empirical trend of higher aphid densities in September plantings and progressively less dense populations in the October–December plantings. It is hypothesized that there was differential exposure to aphid colonization among plantings. A pooled estimate ofαandβwere used to determine the number of samples required to obtain an estimate of the mean density ofP. populitransversusin crucifers within 10 and 25% of the true mean. An alternate method of population estimation, using a presence–absence sample, was also presented.