Abundance, persistence, and variability of populations of Macrosiphum euphorbiae (Thomas), Myzus persicae (Sulzer), and Aphis nasturtii Kaltenbach (Hemiptera: Aphididae) in potato plots for intervals of 58 years (n = 1), 29 years (n = 2), 19–20 years (n = 3), and 9–10 years (n = 6) were compared. The abundance of M. euphorbiae showed no trend among decades and varied 2.4-fold, whereas that of M. persicae and A. nasturtii declined and showed 54-fold and 3700-fold variation, respectively. All three aphid species persisted through the first five decades and M. euphorbiae also persisted through the sixth (last) decade, but M. persicae and A. nasturtii failed to persist for 1 and 3 years of the last decade, respectively. Population variability (a proportion between 0 and 1) measured over a 58-year interval was high: 0.585 for M. euphorbiae, 0.771 for M. persicae, and 0.830 for A. nasturtii. During the first three but not the last three decades, population variability increased with sampling interval, owing to dramatic declines in abundance for M. persicae and A. nasturtii and one stable decade for M. euphorbiae, but no evidence of a more-time — more-variation effect was detected. Persistence was not related to population variability, but declined with abundance. Populations did not reach equilibrium, because of declining abundance for M. persicae and A. nasturtii and changes in population variability from decade to decade for M. euphorbiae. Populations of M. persicae and A. nasturtii from this crop monoculture were less stable than previously studied natural populations of a native aphid species. In contrast, the population of M. euphorbiae, a native species, had variability in a potato crop similar to that of the previously studied native species. The high population variability of M. persicae and A. nasturtii may be associated with their status as introduced species. The dynamic and species-specific characteristics of population variability require that interspecific comparisons be considered cautiously.

Stability (temporal variability, persistence, resilience) was assessed over 8–13 years for subpopulations, populations, and regional populations of Uroleucon rudbeckiae (Fitch) (Hemiptera: Aphididae) in southern Manitoba, Canada. Contrary to expectations, natural populations of this native aphid were not more stable than those of aphids inhabiting crops. Among population parameters, prevalence (proportion of plants infested) proved more effective for quantifying temporal variability than intensity (colony size) or abundance (number of aphids per stem). The parameter “population variability” was a more effective index of temporal variability than the standard deviation of the logarithm or the coefficient of variation. Small differences in temporal variability were detected among populations that varied greatly in size. Population variability declined slightly as spatial scale increased and did not increase consistently over time. Population variability can be considered characteristic of this species in southern Manitoba, having a value of 0.648 ± 0.080 (mean ± standard deviation, n = 5, over 8–13 years) on a scale of 0–1, a high degree of temporal variability. Persistence was not related to temporal variability. Subpopulations were less persistent than populations, and one of five populations did not persist. Small populations were more likely to disappear temporarily. No resilience was detected.

Developmental rate and adult weight were studied at constant temperatures from 9.8 to 27.9°C for 18 clones from each of five populations of the pea aphid, Acyrthosiphon pisum (Harris), from locations between 39 and 53°N latitude in central North America. The response of developmental rate to temperature for each clone was accurately described by a three parameter non-linear equation. Adult weight usually decreased with increasing rearing temperature, but the shape of the response to temperature varied among clones. Variation in the developmental parameters was greater among clones within populations than among populations. No consistent trends were observed in the developmental parameters or adult weights either with latitude or the long term average temperatures at the locations. We conclude that previously reported geographic variation in the developmental threshold of this species, which was attributed to local adaptation, occurred either because the clones tested were not representative of the populations or because rearing methods differed among studies. The results are discussed in relation to the hypothesis that life history traits which are temperature sensitive are adapted to local thermal environments.

In a study of male alary dimorphism, clones of pea aphid, Acyrthosiphon pisum (Harris), were collected five times over two seasons in one location and once each from three other latitudes in the Great Plains region of North America. All clones produced some males when subjected to a short photoperiod (L14 : D10 or L13 : Dll) at 20 ~ The presence of three distinct classes of clones based on the morph of males they produced (apterous only; alate only; apterous and alate in equal proportions) provides evidence for a genetic basis for the dimorphism. The relative frequencies of clones producing only apterous males varied geographically, providing some evidence to support the hypothesis that populations are not panmictic over the Great Plains region.

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