Insect pests201042223143 by lindayy


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									Ins e c t p e s ts

Nematodes take on the battle of the bugs
                                                                                               18 species or Heterorhabditis, with eight
  O      ne of the world’s tiniest creatures
        is proving an invaluable tool in
the biological control of insect pests
                                                 by Malcolm Robertson,
                                                                                               species. The infective juvenile EN is
                                                                                               almost microscopic, ranging from 0.5
which affect a wide variety of crops.                                                          millimetres to 1.5mm long, depending on
   CSIRO researchers have found                                                                species. It has a closed mouth and anus
nematodes are able to invade and kill a                                                        and cannot feed until it finds an insect.
large number of insects which, left
unchecked, are capable of causing large-
scale crop damage.
   And this use of biopesticides has the
potential to increase organic fruit prices
and minimise harm to natural enemies
                                               The symbiotic bacterium produced by invading
without causing any environmental              nematodes convert the body matter of the
pollution.                                     dead insect into food to nourish a new
                                               generation of nematodes which are then
   Apart from insects, nematodes are the       released into the soil to continue the cycle.
next most common animals on earth,             rotation. But after nematodes are
with nearly a million different species.       introduced into a forest they can be left
They are found almost everywhere,              unchecked to infect wasps because sirex
from the tops of mountains to the              females transmit them throughout the            A scarab beetle which has been invaded by
depths of the oceans.                                                                          nematodes. Once inside a beetle the
                                               population.                                     nematodes release a bacterium which kills the
   Most nematodes are harmless but                But nematodes that might be used to          insect rapidly.
some are dangerous, including                  control other insect pests seek out and             Usually found in soil, the nematode
roundworms that affect livestock and the       kill the various pests and work therefore       detects insect movement and then
eel worms that cause billions of dollars       similar to insecticides, killing insects        follows a trail of carbon dioxide to find
damage to crops worldwide.                     only near to where they are applied.            the insect. It is important that there is a
Worms as pest control workers                     These nematodes are known as                 water film between the nematodes and
   Despite their small size, nematodes         Entomopathogenic nematodes(ENs).                the pest which the ENs can move
are proving a big asset in the fight           CSIRO was the first organisation in the         through to reach their targets. The
against pests.                                 world to use ENs commercially; against          nematode enters the insect’s blood where
   The first instance of nematodes being       black vine weevil in ornamental plants          it kills it. ENs enter through the insect’s
used successfully for insect pest control      from 1981 and against currant borer             natural body openings; the mouth, anus
was in Australia nearly 30 years ago.          moth in black currants from 1983. Since         or respiratory inlets (spiracles) and then
CSIRO introduced a nematode which              then, various ENs have been introduced          penetrate into the blood cavity from the
sterilises the sirex wasp, the main pest of    around the world to control a variety of        gut or breeding tubes.
Australia’s one million hectares of pine       pests, though control is usually in niche           The Heterorhabditis species can
forest.                                        markets.                                        penetrate through the interskeletal
   Without control it is estimated the         Nature’s guided missiles                        membranes (chinks in the insect’s
Sirex wasp could cause $1-4 billion loss          Most ENs belong to one of two types          exoskeleton) by scratching away at these
in tree death for every 35-year forest         - Steinernema of which there are about          with a special tooth.

              Once in the insect’s blood, the EN
           infective juvenile releases a bacterium
           found only in ENs which multiplies
           and kills the insect after about a day.
           The bacteria then convert the insect
           into suitable food for the nematodes
           and produce a range of antibiotics and
           anti-feedants that preserve the dead
           insect while the nematodes feed and
           breed within it.
              After about 10 days a medium-sized
           insect cadaver may produce up to
           100,000 or more infective juvenile ENs
           that are released into the soil and seek
           out new insect pest hosts.
           Production and use
              CSIRO Entomology research in             CSIRO scientists Robin Bedding and Karen Butler collecting insects from beneath a
                                                       playing field, Canberra, Australian Capital Territory. Ongoing research will see more
           Australia and overseas has shown ENs        suitable nematode species identified and developed for a use against a wider range of
           to be effective against a range of insect   insect pests.
                                                       formulation can be readily mixed in           temperatures more than 30˚C. But a
              These include scarab beetles on
                                                       spray tanks, sprayed without blocking         few species can survive, though are
           amenity turf, ornamentals and blue
                                                       nozzles and can survive several months        unable to infect pests, at temperatures
           berries; fungus gnats on plant
                                                       at room temperature.                          less than 0˚C.
           nurseries, hydroponics, and mushroom
                                                          The long shelf-life has been
           houses; weevils on ornamentals,                                                           Looking to the future
                                                       achieved by manipulating the
           strawberries, cranberries, citrus and                                                        The use of ENs is still in its infancy
                                                       nematodes’ physiology to cause them
           bananas; cutworms, webworms,                                                              and there is considerable potential yet
                                                       to enter into hibernation. When in
           billbugs and mole crickets on amenity                                                     to be fulfiled. New species and
                                                       hibernation they use only one per cent
           turf; termites in houses and trees;                                                       strains are constantly being found and
                                                       the oxygen of non-hibernating
           peach borer moth in apples in China;                                                      can now be stored in liquid nitrogen
                                                       nematodes and can last significantly
           carpenter worm in shade trees in China                                                    indefinitely to preserve genetic
                                                       longer, provided no fungal
           and fig trees in the United States.                                                       diversity.
                                                       contamination develops and a precise
              To use ENs in insect, control                                                             As more durable and more suitable
                                                       water content level is maintained.
           researchers select the best nematode                                                      strains become available through
                                                          Unfortunately, ENs cannot be
           species, and the best strain of that                                                      collection, selective breeding and other
                                                       applied as simply as insecticides.
           species, produce it in vast numbers and                                                   manipulations, more insect pests can
                                                       Being living organisms, they can be
           apply it evenly so larger numbers of                                                      be targeted and fewer ENs will be
                                                       damaged by ultraviolet light and will
           ENs can reach each insect pest.                                                           required for treatments, reducing the
                                                       only survive in moist environments as
              It takes about 2000 million ENs to                                                     cost. There is also much research being
                                                       they need a water film to move through
           treat one hectare and CSIRO has                                                           carried out on methods for applying
                                                       to reach their targets. They will also
           patented a method to mass produce the                                                     ENs which should help reduce
                                                       sediment in spray tanks if not agitated
           nematodes.                                                                                treatment costs further.
              Because ENs are living organisms                                                          For more information contact
                                                          Because nematodes are susceptible
           which require oxygen, it is impractical                                                   Robin Bedding, CSIRO Entomology,
                                                       to UV light they are best applied at
           to supply them to users in a water                                                        on phone (O2) 6246 4294 or fax
                                                       dawn or dusk. The ideal time is at dusk
           suspension. The water would have to                                                       (02) 6246 4298
                                                       so they can become active at night
           be aerated continually and even this
                                                       without risk of sunlight damage.
           would only last for a few days.
                                                          ENs cannot infect at temperatures
              But CSIRO Entomology has
                                                       less than about 15 degrees Celsius and
           patented a number of better ways of
                                                       many species become stressed at
           formulating ENs. This latest


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