PEST

NAME
Plague Thrips, Blossom Thrips
Thrips imaginis

ORDER
Thysanoptera

Description of the Pest
This slender grey insect is up to 1.2mm long and the folded fringed wings appear as silvery stripes. They are difficult to see singularly and the yellowish wingless nymphs are smaller. Both adults and the first two nymphal stages have rasping and sucking mouthparts.

     

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

Life Cycle
This insect has 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. The effect is a reduction in fruit and seed production on the host plant.

Susceptible Plants
Plants that produce buds and petals that are soft are at most risk, such as Alyogynespecies, Baeckeaspecies, Hibbertiaspecies, Hibiscusspecies and Leptospermumspecies. There is also a wide range of ornamentals, apples, pears, citrus, stonefruit, grapes and strawberries that are attacked.

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.

BiologicalControl
No effective natural control though heavy rain reduces numbers.

Chemical Control
Thrip can be sprayed with a contact insecticides at least twice every ten days to kill newly hatched nymphs.
Note
Always read the label for registration details and direction of use prior to application of any chemicals.