PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
BIOLOGY & IDENTIFICATION
Phylum Mollusca, Class Gastropoda
NO. SPECIES
IN AUSTRALIA
SOME
DISTINCTIVE
FEATURES
About 10 of the 50 introduced species have become serious pests of
agricultural and horticultural crops in Australia. There are more than
1000 native species, none are important pest species. Many Australian land
molluscs are endangered and some Australian species are already extinct.
There is no evidence that exotic species have affected the survival of Australian
native species, as most introduced pest species invade places only after humans
have destroyed the habitat of native snails. Museums are identifying and databasing
virtually all the available collections of Australian Land Snails.
Land Snails of Australia – Museum Collections
www.environment.gov.au/biodiversity/abif/bat/snails.html
Slugs and snails are many-celled animals with a true digestive cavity.
SHELL
1. Unsegmented soft bodies of snails and slugs are covered with
a mantle (layer of tissue) that usually secretes a limey shell.
2. Snails have an external, spirally-coiled shell carried on the
back, into which the snail withdraws when alarmed or at rest.
3. Slugs resemble snails in general appearance but the shell is
either absent or reduced to a shield-like structure borne on
the forehead of the back. In some slugs the back has a
leathery covering.
If betting on snail races
put your money on the
least slimy snail,
making slime
uses energy
BODY
MOVEMENT
1. Snails and slugs have similar bodies.
2. Bodies are broad and elongate, usually light or dark grey
and of variable length depending on the species. They bear
2 pairs of retractile tentacles on the head.
3. Eyes are at the tips of the 2 nd and longer pair of tentacles.
4. Mouth, below the tentacles, contains a file-like organ or
radula which is used for rasping off portions of food.
Snails and slugs glide along by undulating the muscles of the
foot over a slippery track of mucous secreted by glands in the
foot. The mucous solidifies on exposure to air, this is the
silvery trail left by snails.
Shell
Eyes
Foot
Diagram of a snail
Tentacle
Mantle
Eyes
Foot
Diagram of a slug
Tentacle
METHOD OF
FEEDING
Snails and slugs feed by rasping the surfaces of a wide range of plants. They
feed at night and return to hide under debris, stones and plants during the day.
They only feed during the day during prolonged wet weather. Slugs can
eat their body weight in a day and eat large areas of newly emerging crops.
228 Snails and slugs