57
As yet, no indigenous entomopathogenic nematodes have been commercialised in South
Africa and the research therefore supports efforts to harness our rich biodiversity for the
benefit of the local agricultural sector.
With such a product, several soil-borne insect pests could be targeted, including the black
maize beetle, cutworms, false wire worms (larval and beetle stages;
Photo 2
), wire worms
and thepupaeof theAfricanbollworm residing in the soil.
As these insect pests have different behaviours and occupy specific environmental niches,
the use of the correct entomopathogenic nematodes against a particular pest species
is critical.
Essentially, three types of IJs are recognised by their foraging strategy, i.e. the cruiser-type,
ambusher-type and an intermediate-type (a combinationof both cruiser and ambusher).
As the name suggests, the first type actively seeks their host in the soil environment,
while the second type lies waiting for the host to pass by, whereupon the IJ will latch onto
the insect.
The intermediate strategists are adapted to infecting insects that occur just below the
soil surface, such as prepupae of moths, fungus gnats, and/or weevil larvae. The sit-and-
wait-strategists or ambushers are characterised by lowmotility and a tendency to stay near
the soil surface.
They tendnot to respond tovolatileandcontact host cuesunlesspresented inanappropriate
sequence, and thenefficiently infectmobilehost speciessuchascutwormsandmolecrickets
near the soil surface. At the other extreme, the widely foraging strategists or cruisers are
characterisedby highmotility and aredistributed throughout the soil profile.
In soil, the infective juveniles can disperse almost 1 m in both horizontal and vertical
directions within 30 days. This dispersal, especially for cruiser-type nematodes, allows the
entomopathogenic nematodes to actively seek out their hosts.
Factors influencing the motility of infective juveniles are moisture, temperature and soil
texture, of whichmoisture is themost critical, because the nematodes need a water film in
the interstitial spaces of soil for effectivepropulsion.
Different nematode species/strainshavedifferent temperatureoptima and ranges that affect
their survival and hencemotility. Nematodes losemotility at low temperatures (<15°C) and
become inactivated at high temperatures (>30°C).
Soil porosity affects nematode dispersal with less dispersal occurring as soil pores become
smaller. Nematodes can also be dispersed great distances, passively by water, as well as
by wind, infected hosts, human activity, etc. which may in part account for their wide-
spreadglobal distribution.
Entomopathogenic nematodes are commercially available internationally for application
in residential gardens, golf courses and agricultural fields. They are infectious to over
200 insect pests including important pests of grains, vegetables, sugarcane and forestry.
Some entomopathogenic nematode species have shown good compatibility with chemical
pesticides and other biocontrol agents. These entomopathogenic nematodes can therefore
be safely incorporated into an integratedpestmanagement strategy.
They furthermore do not require special equipment for application. They can be applied
using standard spray equipment for chemicals and through existing irrigation systems.
The development of entomopathogenic nematodes based products by the ARC-SGI is
being conducted in collaboration with the local company Plant Health Products (Pty) Ltd in
KwaZulu-Natal and theAdnanMenderesUniversity inTurkey.
To date, cooperation between the ARC-SGI and PHP (Pty) Ltd has led to the successful
registration of the biopesticide Eco-Bb, an environmentally friendly product based on the
insect-killing fungus
Beauveriabassiana
(see
.
For further information, contact Tshima Ramakuwela or Dr Justin Hatting at
theARC-SGI on 058 307 3400.
