Insects of Southern Australian Broadacre Farming Systems - Grains ...

Figure 5.2 Schematic moth lifecycle and associated parasitoid (wasp)
Un-parasitised
Moth
Eggs
Moth pupae
Caterpillar
Parasitised
Lifecycle broken here by larvae
and pupae parasitoids
Parasitic wasp
emerges
Moth
Parasitic wasp
cocoon develops
Eggs
Lifecycle broken
here by egg
parasitoids
Parasitic wasp laying
an egg in a caterpillar
Source: C. Paull (SARDI)
Insects of Southern Australian Broadacre Farming Systems Identification Manual and Education Resource © 2012
Disease-causing micro-organisms
and pathogens
Fungi: Fungi are the most common diseases of insects.
Fungal spores that come in contact with insects
germinate under certain conditions and fungal hyphae
penetrate the insect’s skin (cuticle), often releasing
toxins. The fungus grows inside the insect body and
leads to its eventual death. Useful genera: Beauveria,
Entomophthora, Hirsutella, Metarhizium, Nomuraea and
Verticillium.
The disadvantages of fungi include:
• sporulation and germination require ideal conditions
(adequate moisture and humidity) to affect control in
the field of large pest populations;
• difficult to mass produce consistently for
commercial use and have a limited storage life.
Metarhizium is available for locust control (e.g. Green
Guard TM ).
Viruses: Many viruses infect and kill insects. This occurs
mainly via viral proteins damaging the insect’s gut lining.
Several useful naturally-occurring viral groups include:
the nuclear polyhedrosis viruses (NPVs), granulose
viruses (GVs), cytoplasmic polyhedrosis viruses
(CPVs), and entomopoxviruses (EPVs). NPV is available
commercially (e.g. Gemstar TM ).
6
SECTION 5 IPM Principles and Case Studies
Bacteria: Bacteria rarely kill insects but one species,
Bacillus thuringiensis (Bt), and variants of the strain have
been widely used as a biocontrol agent.
Bt is mainly used against caterpillar pests (Lepidoptera)
but is also active against some beetles (Coleoptera) and
mosquito larvae (Diptera). It is formulated as a dust or
as granules and then applied as an aqueous spray.
The bacteria need to be applied when pest larvae are
young as there is a delayed killing action. Bt toxins are
also produced in some genetically modified crops such
as cotton and corn. Check out the Bt checklist on page
13 in this section.
Nematodes: Nematodes are microscopic invertebrates
with a smooth, cylindrical body and no legs. They
actively search for their host, then enter the body
through natural openings where they release bacteria
that digest the insect. The nematodes then feed on
the bacteria/insect slurry. Eventually the dead insect
bodies rupture and release further nematodes. Some
nematodes are commercially produced as a dehydrated
cellulose mixture, which is rehydrated before use in high
value crops.