Climate change implications for the pest status and vectoring potential of the bird cherry-oat aphid, Rhopalosiphum padi

Aphids are likely to adapt to climate change given their short generation times, low developmental threshold temperatures and efficient dispersal capabilities. Surprisingly little is known however about their vectoring ability and the indirect effects to their hosts with climate change. In-depth analysis of the interactions of a single host-pest-pathosystem provides an exemplar system from which climate change effects can be elucidated.

We have focused on the bird cherry-oat aphid (Rhopalosiphum padi); one of the major pests of temperate cereal crops worldwide, notable for its extensive Poaceae host range and as a prominent vector of the wide ranging highly destructive yellow dwarf virus (YDV). The two foremost factors influencing aphid vector population dynamics and the subsequent incidence and severity of YDV infection in host plants are the persistence (survival and abundance) of the vector and the timing, rate and extent of dispersal and migration events.

The main direct effects of climate change on R. padi persistence is elevated temperature leading to faster development rates and higher fecundities and reduction in winter mortalities at least up to an upper thermal threshold. Vector virus interactions were altered with greater virus inoculation and transmission efficiencies at higher temperatures. All effects were more pronounced on the apterae populations. The accompanying effects of elevated CO2 are less clear but may cause reductions in population levels. Colonisation of wheat by aphid vectors is a direct consequence of aphid movement via dispersal or migration events, the magnitude of which can affect the occurrence of YDV infections in the crop.

Elevated temperatures will shift timing and duration of lower and upper thermal thresholds that determine flight. Flight patterns will be disturbed by projected increases in wind strengths possibly leading to larger and longer range migration flights. Alternatively heavy precipitation will hamper aphid take-off and flight leading to poor colonisation by alates. Drought stressed plants encourage movement of R. padi nymphs and apterae. Finally, seasonal variation in precipitation will vary population dynamics. Late summer and early autumn rainfall, for example, is a determinant of population size colonising winter cereals in Australia.

The qualitative analysis of R. padi biology with the influence of climate change is being used to construct an integrated R. padi-virus-wheat model to quantitatively assess the yield impacts of YDV infections under future climates.