PEST

NAME
Thrips (General)
Various Thrip Species

ORDER
Thysanoptera


Description of the Pest
There are many species of thrips that attack living and dead plant material. The winged adults are black, yellow, white or brown with slender bodies and up to 2mm long. The folded fringed wings appear as silvery stripes and the smaller nymphs are difficult to see, but are wingless simular to the adults. Both adults and the first two nymphal stages have rasping and sucking mouthparts.

Thrip species

Boree Gall(Kladothripsspecies) adults are gall producing thrips that form smooth bubble-like or irregular spiny growths on the leaves. These galls can contain up to 1000 insects that also reproduce inside, and are trapped until the gall dries or splits open. Commonly found in inland areas attacking the phyllodes of Acacia species.

Glasshouse Thrips(Heliothrips haemorrhoidalis) is a slender up to 15mm long with small fringed wings. The adult lays eggs on the underside of leaves where the nymphs emerge as miniature adults but wingless. Then feed on the soft leaves leaving a silvery mottled appearance.

Appearance and Distribution of the Pest
Thrips are found from tropical to temperate regions preferring a cool mild winter followed by a dry sunny spring that produces abundant flowers and new foliage. It is dispersed by flying and can be carries great distances on the wind.

Life Cycle
These insects have a Hemimetabolouslife cycle, ie. When the immature nymphsresemble the adults.
The female adult lays her eggs using an oviposit in a slit on flower stems or occasionally leaves. The eggs develop into four nymphal stages. The first two stages occur on the plant and the last two in the surrounding soil or in leaf litter, emerging as adults and flying to reinfect the plant. It takes ten to thirty days to develop from egg to adult depending on the temperature and rainfall. Under opium conditions thrips are produced in plague proportions.

Period of Activity
Thrips are most active during warm dry, calm weather, but dislike the soil to be too dry or wet.

Damage Caused
Thrips congregate inside the flowers damaging the epidermal layer, allowing sap to leak out. This causes the flower petals to become brownish and curl along the margins. They also attack the upper surface of leaves causing a silvery discolouration as they suck the sap. The effect is a reduction in fruit and seed production on the host plant.

Susceptible Plants
Generally many plants species are attacked by thrips including buds, petals and leaves that are soft are at most risk, such as Alyogyne, Baeckea, Hibbertia, Hibiscusand Leptospermumspecies. There is also a wide range of ornamentals suseptable to attack including apples, pears, citrus, stonefruit, grapes and strawberries.

Buddlejaspecies may be attacked by the thrip (Hercinothrips femoralis).

Cordyline, Agave, Dracaenaand Howeaspecies, Ficus elasticaare attacked by the Dracaena Thrips(Parthenothrips dracaenae) which feed of the leaves.

Knightia excelsais attacked by thripsby feeding on the chlorophyll in the leaf causing significant paling of the leaves. Stresses plants are more susceptible and plants rarely die from attack.

Peperomia, Cissus,Tropaeolumand Passifloraspecies and some fern speciesare attacked byGlasshouse Thripswhich can cause heavy damage in inclosed areas such as a glasshouse.

Watsoniaspecies are attacked by the Gladiolus Thrips(Taeniothrips simplex).

Cultural Control
There is no satisfactory cultural control. Small infestations may be ignored or the plant may be hosed to reduce the numbers. Removal of surrounding leaf litter, weeds and cultivating the soil can also reduce the numbers and disturb the life cycle. Care should be taken not to remove flowering weeds under trees that are in bloom as the thrips may migrate on to the tree, alternatively flowering annuals can be planted under trees to attract the thrips away.

BiologicalControl
No effective natural control though birds; wasp and other predators eat thrips. Weather conditions such as heavy rain help reduces numbers.

Chemical Control
Thrips can be sprayed with Dimethoate or Maldison at least twice every ten days to kill newly hatched nymphs, but may have a detrimental effect on other insects such as bees.
Note
Always read the label for registration details and direction of use prior to application of any chemicals.