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Towards more sustainable control of the
Russian wheat aphid
F
ollowing the release of the first Rus
sian wheat aphid (RWA),
Diuraphis
noxia
(
Photo 1
), resistant cultivar
(Tugela-DN) in 1992, host plant re
sistance has become the backbone of Rus
sian wheat aphid control under dryland
conditions in the summer rainfall region.
However, since the arrival of the first aphid
biotype, RWASA1 in 1978, three subsequent
biotypes, RWASA2, RWASA3 and RWASA4,
have made their unwelcome appearance.
The development of these aphid biotypes
is not unexpected, as widespread deploy
ment of host plant resistance implies evo
lutionary adaptation, fuelled by climate
change and a higher selection pressure im
posed upon the aphids by host plant resist
ance (i.e., survival of only those individuals
that have the inherent ability to overcome
the resistance).
To counteract such selection, indiscrimi
nate mortality inflicted by natural enemies
(predators, parasitoids and pathogens), is
seen as a critical component in a host plant
resistance x natural enemy-based control
programme. Pathogens are disease-causing
entities and include microbes such as fungi,
viruses and bacteria; collectively referred to
as entomopathogens.
As part of an integrated pest management
(IPM) approach against Russian wheat
aphid, ARC-Small Grain explored the com
bined use of host plant resistance and the
insect-killing fungus (also referred to en
tomopathogenic fungus),
Beauveria bassi-
ana
. These field trials resulted in about
65% fewer Russian wheat aphid in treated
plots compared to controls.
In an attempt to further improve this level
of efficacy, research was initiated on the
combined use of
B. bassiana
with botani
cally based insecticides; potentially exploit
ing any synergy between the two biocontrol
agents. Moreover, bio-insecticides are con
sidered favourable alternatives to address
chemical insecticide issues relating to hu
man poisoning, residues, environmental
pollution, insect resistance and negative ef
fects on non-target organisms.
Notably, use of chemical pesticides may
negatively affect human health and bio
diversity as it is estimated that less than
0,1% of a sprayed pesticide actually reaches
the target site; the rest ends up in the en
vironment. Effective bio-insecticides can
ensure a better quality of life as many em
ployees on commercial farms are confront
ed by the risk of being exposed to sub-lethal
doses of chemical insecticides.
During 1990, 15% of South Africa’s entire
economically active workforce (1,18 million
people) were working on >62 000 South
African farms, while 20% of farm workers
involved in chemical applications were il
literate (implying poor or non-adherence
to label warnings). In fact, in 2002, around
Focus
Integrated pest control
Nokulunga Mzimela
and
DR Justin Hatting,
ARC-Small Grain, Bethlehem
1: Russian wheat aphid,
Diuraphis noxia
colony, clustered on a wheat leaf.
Photo: Kobus
Dreyer, ARC-Small Grain
2: Flower of the Dalmatian chrysanthemum,
Tanacetum cinerariifolium
.
Photo: KENPEI,
https://commons.wikimedia.org/w/index.php?curid=2210117
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