In some aphid species, such as Sitobion avenae and Myzus persicae (in the photo below from Invasive.org), overwintering is not reliant on eggs, so that the interaction between the cold tolerance of active stages and the severity of winter temperatures may have a dominant effect on their subsequent population dynamics in terms of the timing of migrations and seasonal abundance.
According to literature data, Myzus persicae could produce genetically distinct clones, both in the holocyclic and anholocyclic life cycle, leading to the possibility that clones differ in their activity thresholds, and, as a consequence, any pattern in thermal tolerance will depend on the composition of the population. In particular, if activity thresholds are related to the latitude of aphid collection, it could be possible to hypothesize that aphid clones from colder climates where sub-zero temperatures are more common, e.g. Scandinavia, would display greater cold adaptation. At the same time, Scandinavian clones should display a reduced recovery time from chill coma. In contrast, a clone from a warmer climate where sub-zero temperatures are unlikely, e.g. the Mediterranean, would be hypothesized to display greater heat adaptation, but a reduced cold adaptation… but is it really true?
Alford et al. evaluated the activity thresholds in nine anholocyclic clones of the peach-potato aphid M. persicae collected along a latitudinal cline of its European distribution from Sweden to Spain. Interestingly they showed that high-temperature activity thresholds were less plastic comparing clones than low-temperature thresholds. Furthermore they showed that aphid thermal tolerance could be governed more by clonal type than the latitudinal origin of the populations and that aphids of the genus Myzus have little or no ability to maintain the acclimation process over successive generations.
However, the absence of acclimation seems not be a general feature in aphids… since Powell and Bale showed that low temperature exerts an intergenerational effect resulting in increased cold tolerance in the grain aphid Sitobion avenae with a preferential investment of increased cold tolerance in first born progeny through successive generations.The reported intergenerational increases in cold tolerance can be seen as part of a more generalised ability of aphids to exhibit between-generation directional changes in response to a stress or other environmental perturbation that persists over longer periods of time, such as changes in temperature, host plant quality or carbon dioxide (CO2) concentration.
The ability of aphids to have inherited acclimation or other faster adaptation mechanism seems to be at present still controversial and it could be interesting to have data also on other aphid species since most of the studies on acclimation and thermal tollerance have been mainly performed on S. avenae and M. persicae leaving almost unexplored other intriguing aphid species.
References
- Alford, L., Blackburn, T., Bale, J. (2012) Effects of acclimation and latitude on the activity thresholds of the aphid Myzus persicae in Europe. Journal of Applied Entomology, 136, 332-346 DOI: 10.1111/j.1439-0418.2011.01658.x
- Powell, S., & Bale, J. (2008) Intergenerational acclimation in aphid overwintering Ecological Entomology, 33, 95-100 DOI: 10.1111/j.1365-2311.2007.00947.x
