| In February 2001, red
imported fire ants (Solenopsis invicta) were detected near the Port
of Brisbane. The invasion of these pests from North and South America
has sparked a massive eradication campaign that currently covers over
40,000 hectares in the Brisbane region.
Fire ants are extremely serious pests that have the potential to devastate
our environment and severely impact on agricultural production. As their
name implies, they also posses a painful sting, and pose a serious health
threat to humans and livestock.
Although fire ants are known to be predators of heliothis, two recently
published studies of the impact of fire ants in cotton crops in southern
US present some worrying results that should be a ‘heads up’
for Australian cotton growers.
Beneficials under ‘fire’
A team of researchers at Auburn University in Alabama has demonstrated
that fire ants form mutualistic* associations with cotton aphids (Aphis
gossypii) and vigorously defend aphids from predators like lady beetle
larvae and lacewing larvae.
Fire ants can feed on the honeydew produced by aphids and many other
sucking pests. In return fire ants ‘nurture’ the aphids,
and attack and kill any predators they encounter. The researchers found
that in cotton fields with high densities of fire ants, cotton aphids
were much more abundant, and ladybeetles and lacewing larvae became
less abundant.
In a series of field and greenhouse experiments, the researchers quantified
the impact of fire ants on a range of beneficial insects and spiders.
They found that as the density of fire ants increased it was clearly
correlated with significant reductions in the densities of ladybeetles,
lacewings, big eyed bugs, pirate bugs, damsel bugs, assassin bugs, predatory
beetles, wasps and spiders.
Australian cotton producers are making great headway in reducing the
amounts and severity of insecticides used to control insect pests. Part
and parcel of this IPM approach relies on nurturing healthy populations
of beneficial predators and parasites as biological allies. The last
thing we need is an aphid-friendly pest to come and displace them! Especially
a pest that makes field work in cotton crops dangerous to humans. Fire
ants are spreading in many cotton farming areas in the southern US —
we need to be alert to prevent them establishing in Australian cotton.
Fire ants are small. They are reddish-brown in colour on the head and
body, with a darker abdomen. They usually make dome shaped nests up
to 40cm high — but in cultivated areas like crop fields nests
may not form domes.
The distinguishing features of fire ants are:
• A single nest contains ants in a wide range of sizes from
two mm to six mm;
• They tend to swarm out of the nest from multiple exits
when disturbed; and,
• They attack by crawling onto people and animals before
suddenly all stinging in unison.
Fire ants are easily spread in soil, mulch and similar gardening materials.
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