Contents - Greenmount Press

Overwintering strategy of
solenopsis mealybug
■■by Moazzem Khan 1 , Melina Miles 1 , Susan Maas 3 , Kristy Byers 1 and Gail Spargo 2
Insects use overwintering as a strategy to survive adverse
weather condition such as cold winter. An effective
overwintering strategy maximises an insect’s chance of
surviving adverse weather conditions.
Insects have a range of overwinter strategies. Some enter
diapause, such as Helicoverpa armigera diapausing as pupae,
while others may continue development but at very slow pace as
in green mirid. Understanding overwintering strategy is the key
to developing a management strategy for the pest. For example,
pupae busting exploits an opportunity to control H. armigera
without insecticides; resulting in population management and
reducing carryover of insecticide resistance.
Solenopsis mealybug is an emerging pest of cotton in
Australia. The first outbreak occurred in the 2008–09 and 2009–
10 seasons in the Burdekin and Emerald. In 2010–11 another
outbreak occurred in Byee, 40 km north of Kingaroy, in dryland
Bollgard cotton. Solenopsis mealybugs cause damage to cotton
from emergence to maturity by sucking sap. Overwintering
populations within a field with a history of mealybug probably
will start colonising emerging plants. Therefore, a better
understanding of solenopsis mealybug overwintering will
contribute to the development of a management strategy for this
pest.
How does solenopsis mealybug overwinter
To understand the solenopsis mealybug overwintering strategy
we conducted a survey from August to October 2011 in Byee in
the same field where the outbreak occurred and again from July
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to September 2012. In 2011 the survey commenced after pupae
busting. In 2012 the survey commenced when cotton still was in
the field, prior to picking.
Solenopsis mealybugs were found on non-crop hosts including
stagger weed, bind weed, rasp weed, marshmallow, verbena,
pigweed and wild radish. The survey showed that solenopsis
mealybug overwinter mainly as nymphs (86 per cent in 2011 and
94 per cent in 2012) (Figure 1) but develop at a slow pace. At the
end of August as temperatures start to rise, adults start emerging
and infest cotton once it is planted.
The survey also revealed that more than 70 per cent of
mealybugs were found in the root zone of the overwintering
hosts. Under the soil, temperatures are higher and more
consistent than air temperatures, which is probably why
mealybug colonise roots during the winter. In a clean fallow,
solenopsis mealybug can survive under the soil for quite some
time without any plant host. Once plants start to emerge after
rain the mealybug quickly colonise on that plant (Photos 1 and
2). We also noticed that solenopsis mealybug use any plants to
survive – even plants which are not a preferred host. For example
FIGURe 1: Numbers of solenopsis mealybug on
overwintering hosts at Byee in 2011 (A) and in
2012 (B) – an average of mealybug found on all
plant species shown for each sampling date
A:
B:
22 — The Australian Cottongrower October–November 2012