These biotypes have different levels
of virulence against different Russian
wheat aphid resistant wheat cultivars, with RWASA4 being the most
virulent and RWASA1 the least virulent biotype (Fig. 2). During 2015
the Russian wheat aphid infestation
in major wheat production areas in
South Africa was low with 32.5% of
fields monitored in the Free State
showing no infestation (Fig. 3).
RWASA4 was dominant, making up
19.12% of the biotype complex (Fig.
3). RWASA1 was distributed
throughout the western and central
Free State and Northern Cape, with
no other biotypes occurring in these
areas (Fig. 3). The other biotypes
were concentrated in the Eastern
Free State (Fig. 3). Russian wheat
aphid infestation was very low in the
Western Cape during 2015 with
93.6% of the fields monitored having no infestation (Fig. 4). The only
biotype occurring in the Western
Cape during 2015 was RWASA1 (Fig.
4). This distribution of Russian
wheat aphid can, however, change
as the environmental conditions
change over time. The Russian
wheat aphid biotype complex is dynamic, influenced by environmental
factors such as host plants, altitude
and climate, and can change and
diversify over time causing fluctuation in populations over sites and
years. This dynamic nature of the
Russian wheat aphid will continue to
challenge the development of Russian wheat aphid resistant wheat
cultivars in South Africa. Russian
wheat aphid population dynamics
cannot be understood or predicted
without a thorough knowledge of
the population changes during the
annual cycle. Development, survival
and reproduction data obtained under controlled environmental conditions in the greenhouse are essential
for modelling the population dynamics of Russian wheat aphid biotypes on wheat crops in South Africa.
Fig. 2 Russian wheat aphid feeding damage on susceptible wheat
Increasing temperatures may result
in faster population growth and
shorter life cycles in aphids. This
will result in more generations per
year. Changes in an aphid’s population growth rate could also result in
expanded geographical range or
altered distribution. This change in
distribution may result in pest presure in wheat production areas
where it was previously not experienced. Not only is there the potential for Russian wheat aphid to better survive throughout the year and
build up larger populations earlier
in the season resulting in increased
crop damage as soon as the wheat
emerges, but there is also the potential to expand their range and
become a pest in new areas. In order to mitigate the negative effects
of Russian wheat aphid pressure on
the South African wheat industry as
the climate changes, it is important
to monitor the population growth
and distribution of aphid biotypes
in different areas under different
environmental conditions.
With a changing environment as a
result of climate change there will
be many challenges in future and
each of us have a role to play to
meet these challenges successfully.