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Oktober 2018
50
Integrated pest management is the answer
S
podoptera frugiperda
(Lepidoptera:
Noctuidae) (
Photo 1
), the now fa
miliar fall armyworm, has invaded
South Africa during the 2016/2017
maize production season. This invasion was
met with alarm, awareness was raised and
planning was promptly put into place to
address this new threat.
The problem with invasive species such as
this one is that although a vast amount of
knowledge is available from the Americas,
no information exists on how such a spe
cies will react and settle in the region that
has been invaded. This is especially true
for South Africa, which is situated towards
the southern-most distribution range of this
pest on the continent.
Therefore, more questions were asked
than we had answers for. The question that
everyone asked was: ‘How are we going to
control this pest?’ To answer this important
question, research needs to be conducted
in South Africa, by keeping the local en
vironment in mind and pulling together
current knowledge to search for new
solutions.
For example, fall armyworm was exposed
to insecticide applications for decades in
the Americas and it is well known that it is
resistant to certain products. Similarly, this
pest was also exposed to and effectively
controlled with Bt maize, but it developed
resistance to some products. These re
sistance traits could have come with the
fall armyworm populations that invaded
Africa.
Current local research
Some of the research fields receiving at
tention are: Response of fall armyworm
larvae to genetically modified maize, insec
ticide resistance, host plant range and suit
ability of different South African ecological
regions for pest establishment. Effective
mass rearing of fall armyworm is critical
to support all other research activities and
time is devoted to finding cost effective
rearing systems.
Larvae were collected from fields and
reared on different artificial diets to deter
mine if larvae can survive and complete its
development on these diets. This is needed
to rear adequate numbers of larvae to per
form sound research.
Two artificial diets were compared to
determine the most suitable diet for devel
opment and at the same time, provide a
high survival rate to ensure successful rear
ing. Survival of larvae on both artificial di
ets was more than 90%, which proved both
diets suitable for rearing fall armyworm.
With the challenges of effective larval rear
ing out of the way, a pilot trial was con
ducted to determine larval susceptibility to
genetically modified Bt maize. Larvae were
inoculated onto maize whorls of a non-Bt
maize plant (control), the first generation Bt
maize commercialised in South Africa (Bt1)
and the second generation Bt maize (Bt2).
Larval survival on the control non-Bt maize
plants was 95% after feeding for 14 days,
47% on Bt1 and 0% on Bt2 (
Graph 1
). From
these results, it can be concluded that
Bt1 will suppress the fall armyworm and
Bt2 have the potential to control larval infes
tation.
Use of insecticides
on fall armyworm
For control of fall armyworm with insecti
cides, it is important to adhere to the reg
istration requirements as specified on the
label. Insecticide application forms part of
integrated pest management strategies and
should always be used with care and atten
tion to safety.
It is recommended to keep the following in
mind:
Make sure the product is registered for
control of the target pest.
Read the label thoroughly.
Apply the correct dosage, water vol
ume, with the correct size nozzle.
Determine the best time for optimal
control.
Success of control should also be moni
tored after application. Preventative sprays
for fall armyworm are not viable since the
presence of the pest cannot be predicted
and it will lead to resistance development
against insecticides.
Biological control
A highlight of the past two seasons is that,
although it is an invasive species, the local
natural enemies also started to attack fall
armyworm. A few parasitoids were reared
from fall armyworm larvae sampled from
the field. The most promising discovery was
an egg parasitoid.
This parasitoid, which parasitises eggs of
fall armyworm, is also present and used in
the Americas as biological control agent for
fall armyworm, where it is reared and then
On farm level
Control / Research / Resistance
Integrated pest control
Dr Annemie Erasmus,
ARC-Grain Crops, Potchefstroom and
Proff Hannalene du Plessis
and
Johnnie van den Berg,
integrated pest management programme North-West University, Potchefstroom
Graph 1: Fall armyworm larval survival on conventional and genetically modified maize over time.