Winter climate determines the success of the two main reproductive strategies employed by aphids. Permanent parthenogens survive as parthenogenetic females in mild winters, but are regularly eliminated by low temperatures; while cyclical parthenogens, which switch to sexual reproduction by the end of summer, produce every year fertilised diapausing eggs resistant to frost.
We have studied the variation in sexual morph production of several clones of the cereal aphid Rhopalosiphum padi (L.) showing both strategies. Twenty clones of this species differing by their geographic origin and their mode of reproduction were placed in two laboratory environments mimicking the changes of photoperiod and thermoperiod occurring naturally from the end of summer and during the autumn in oceanic and continental conditions. The analysis of clonal responses in both climatic conditions showed (i) a wide variation in investment of clones in sexual reproduction with, in particular, evidence for a mixed strategy employed by clones producing both sexuals without ceasing parthenogenetic reproduction, (ii) no geographic adaptation among clones belonging to cyclical parthenogenetic populations, (iii) an earlier production of sexuals in continental conditions and a higher production of males in oceanic conditions.
Furthermore, we have compared the dates of first appearance of sexuals in our experiments with those occurring in the field based on a suction trap database and found that sexuals were caught in nature at least four weeks earlier than in the lab. These results underline the need for a better understanding of the influence of the whole array of environmental factors inducing the transition from parthenogenetic to sexual reproduction in aphids., Maurice Hullé, Damien Maurice, Claude Rispe, Jean-Christophe Simon, and Lit
In order to manage the risks posed to domestic crop production by quarantine pests such as Thrips palmi, their potential to establish in a new environment must be assessed. The thermal requirements for development of T. palmi were determined and compared with UK temperatures, to estimate its potential for development under UK conditions. Temperature and rate of development of T. palmi from egg to adult were linearly related between 15 and 30°C, allowing calculation of an overall threshold of 10.1°C, and a sum of effective temperatures of 194 degree-days. In the UK, development of T. palmi would be possible outdoors during the summer when a maximum of up to four or five generations could occur. Comparison of these data with those of the recently established and biologically similar pest, Frankliniella occidentalis, shows that establishment of T. palmi in the UK is unlikely to be limited by an inability to complete the life cycle during the favourable season., Jamie R. McDonald, Jeffrey S. Bale, Keith F.A. Walters, and Lit