45 / 132
New hybrid insect pest spells danger
T
he plant pest environment contains
endless pathogens that can mu
tate, interact with other insects and
microbes and can cause massive
damage to crops. Science has brought us
genetically modified crops, chemical pesti
cides, fertilisers and beneficial microbes to
boost plant growth. Yet, we need to monitor
what is happening in other continents.
Origin of new hybrid pest
The sudden increase in worm infestation
of crops in Brazil caused scientists at the
Australian Commonwealth Scientific and
Industrial Research Organisation (CSIRO)
to respond quickly and the outcome was
identification of
Helicoverpa
bollworms in
cotton, as well as
Heliothis
maize earworms
species and
Spodoptera
(fall army worm
or
herfskommandowurm
), which contains
some 37 species.
Two primary insect pests were cotton boll
worm and American ear worm; and cotton
bollworm is the number one quarantine
pest. Together they can cause billions of
dollars’ damage to field crops globally.
CSIRO had already started analysing the ge
netic make-up of the worms and their moths
a year ago and then completed this process
for both pests (known as sequencing the
genome).
Surprisingly, they found that the two spe-
cies had interchanged genes to produce a
hybrid pest. Moreover, these hybrid insects
are mobile and fly in groups, i.e. hybrid
swarms that contain different genetic com
binations. Mr Robert Cheke in the United
Kingdom also points out that continuous
pesticide use on crops killed targeted pests,
but with GMOs that required much less pes
ticides, different pests came in.
Estimates of potential
impact
The most exposed country seems to be the
USA with their extensive cotton and maize
fields and their relatively close presence to
the hybrid pest in Latin America. In most
of the worm studies in Brazil almost every
worm was a hybrid. Considering that boll
worm has some 100 host plants on which
they feed and that the Australian bollworm
attacks more crops and develops more
resistance to pesticides than the maize
earworm, according to Dr Tom Walsh, im
proved monitoring and countermeasures
are needed in all countries that grow maize,
cotton and soybeans. Mr Craig Anderson,
as lead person of the CSIRO report/article,
estimated that some 65% of American food
production may be at risk.
Clarification of pest
infestations in Brazil
According to Mss Daniela Brioshii from
the Federal University, Rio Grande do Sul,
Brazil, the following explanations on man
agement of Bt crops are still relevant:
Why the sudden pest
pressure in Brazil?
Weather conditions, like drought,
helped larvae survive.
Sequential and successive planting of
host crops – maize, soybeans, cotton,
a common practice – provided shelter
and food, breeding more larvae of the
hybrid pest.
Absence of adequate monitoring.
Crops with Bt genes are more effective
on young but less effective on older
larvae.
Was Bt technology unable to
control pests?
Each Bt technology is developed to control
different pests and cotton bollworm
H. ar-
migera
had not been present in Brazil be
fore.
Recommendations to
manage Bt crops
Even with Bt genes constant monitoring
is necessary.
Under heavy infestation insecticides
may be required.
Integrated Pest Management (IPM) sys
tems can maintain pest population at
lower levels.
Succession of crops is common, but in
secticidal active ingredients with differ
ent modes of action must be rotated to
reduce pests and worms.
Refugia for Bt and non-GM plants are
needed to retain pests susceptible to Bt
proteins.
Insecticide treatment on seeds to plant
for protection.
Use of GM plants is safe and effective
for insect control, but can accommo
date IPM with chemical, biological and
cultural practices.
Bt cotton success in
South Africa
Bt cotton was the first GM crop to be field-
tested in South Africa in 1990. It received
commercial use clearance in 1997. The po
tential risk of bollworm led to crossbreeding
to insert a second Bt gene as precaution,
then a third gene for herbicide tolerance
was added.
In 2018 the technology owner of new stack
ed cotton genes received approval from the
Department of Agriculture, Forestry and
Fisheries (DAFF) for field testing. The cotton
industry applied professional practices and
kept up to date with improved genetic tech
niques. However, the fact that local cotton
crops did not encounter serious bollworm
infestation should not lead to complacency.
The same applies to the successes in yield,
crop genes for resisting maize stalk bor
ers, and use of refugia. Modern resistance
genes have served South Africa well.
It is recommended that we monitor prob
lems in and progress on combatting new
pests like hybrid insects as in Brazil. Inter
national trade in grain and seed is known to
facilitate spread of pests and diseases.
References
Anderson, CJ
et al
. May 2018.
Hybridization and gene
flow in the mega-pest lineage moth
Helicoverpa. Pro
ceedings National Academy of Science. Retrieved
from:
http://www.ncbi.nlm.nih.gov/pubmed
.
Brioshii, D
et al
. January 2014.
Clarifications on pest
infestations in Brazil
. GMO answers. Retrieved from:
http://gmoanswers.com/clarifications-pest-infesta-
tions-Brazil
.
Cheke, RA. July 2018.
New pests for old as GMOs
bring on substitute pests
. Proceedings National
Academy of Science. Retrieved from:
http://www.
ncbi.nlm.nih.gov/pubmed
.
43
September 2018
FoCus
Integrated pest control
Dr Wynand J van der Walt,
FoodNCropBio Consulting and member of Maize Forum Steering Committee
Cotton bollworm.
Photo: CSIRO, Australia