Thermal requirements for development and life table statistics of Aphis gossypii Glover (Homoptera, Aphididae) were determined over a range of constant temperatures from 10 to 30 ~ The lower development threshold and the sum of effective temperatures were 6.9 ~ and 90.1 ~ respectively, for preimaginal development, and 5.8 ~ and 113.6 ~ from birth to the onset of reproduction. Mean total fecundity ranged from 36 larvae per female at 10 ~ to 76 larvae at 30 ~ On a time scale of days, net reproductive rate (Ro) increased with increasing temperature while generation time (T) decreased causing the intrinsic rate of increase (rm) to increase linearly from 0.115 to 0.465. On a day-degree scale rm only varied from 0.019 to 0.028 because the growth of Ro was compensated by an increase in T with increase in temperature. The nearly constant r,~ in terms of day-degrees, over a wide range of temperatures, greatly simplifies the prediction of future population numbers of A. gossypii.

Interpretation of light trap catches of moths is complicated by daily variation in weather that alters flight activity and numbers caught. Light trap efficiency is also modified by wind and fog, and daily weather may effect absolute abundance (numbers actually present). However, actograph experiments and other sampling methods suggest that changes in daily activity are large by comparison to changes in absolute abundance. Daily variation in weather (other than wind and fog) is therefore a form of sampling error in absolute abundance estimates. We investigated the extent of this sampling bias in 26 years of population dynamics from 133 moth species. In a subset of 20 noctuid and geometrid species, daily numbers caught were positively correlated with temperature in 14 species, and negatively correlated with rainfall in 11 species. The strength of correlations varied between species, making it difficult to standardize catches to constant conditions. We overcame this by establishing how weather variation changed with time and duration of the flight period. Species flying later in the summer and for shorter periods experienced more variable temperatures, making sampling error greater for these species. Of the 133 moth species, those with shorter flight periods had greater population variability and more showed significant temporal density dependence. However, these effects were weak, which is encouraging because it suggests that population analyses of light trap data largely reflect factors other than sampling error.

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Abstract. The distribution of the body sizes of British aphids is right‐skewed on a logarithmic axis, as in other taxa. Over the size range 2–5 mm there is a marked decrease in numbers of species with increase in size, which on a log log scale has an exponent of ‐3, The exponent for the right‐hand side of the size distribution of British plants is ‐0.7. The sizes of sixty‐eight species of the genus Aphis are weakly correlated with the size of their respective host plants. An aphid's size is strongly correlated with the length of its proboscis, which indicates the depth to which it has to probe plant tissues in order to feed. On average, trees host more species of aphids than either shrubs or herbaceous plants, which appears to be associated with the relative surface area of specific plant structures. The surface area of plants is mainly made of leaves and most species of aphids are leaf feeders. The largest and least numerous species of aphids feed on the branches and trunks of trees, the proportional cover of which is less than that of leaves. Taking into account all the above observations, a functional explanation in terms of the relative surface area of specific plant structures is offered to account for the size diversity curve of aphids.