Scirtothrips citri

Scientific Name Scirtothrips citri (Moulton, 1909)
Common Names English: California citrus thrips; German: Orangen-Thrips, Kakao-Thrips; Spanish: Trips de los cítricos, trips del cacao; French: Thrips des agrumes;
Description The orange-yellow to yellowish-white or yellow-green body is about 0.9 mm (0.035 inch) long in the female and 0.7 mm (0.027 inch) long in the male. The wings are narrow, and have a fringe of hairs.

Biology

Damage

Citrus thrips puncture epidermis cells to suck out their contents. On fruits, this causes scabby gray or brown scarring. The insects settle mainly under the sepals of the young fruit. The damaged tissue spreads outwards and forms a conspicuous ring. The inner quality of fruits thus blemished is not affected at all: nevertheless, their market value is considerably reduced. Only young fruits, about 3-6 weeks old, are at risk of attack. By the time their diameter reaches 30-40 mm, they are unsuitable as a food source for S. citri.
Young leaves attacked by this thrips may curl and show gray streaks. Extensive feeding on young foliage can lead to shedding of leaves and tree limbs becoming distorted. Healthy, fruit-bearing trees can, however, withstand the damage, and although young trees may become marginally stunted, this does not cause significant economic injury.

Lifecycle

During its lifetime of about 2-4 weeks, each female citrus thrips lays up to 250 eggs, preferably in the soft tissues of young leaves, fruits or green twigs, and in opening flowers.
After 5-15 days, the larvae hatch. The first two nymphal instars feed actively and need 4-14 days for development. The following two instars, prepupa and pupa, do not feed, and they last 3-5 days, which they spend hidden and inactive, mostly on the ground beneath leaf litter, and sometimes in cracks in the bark.
In California, S. citri overwinters in the egg stage, and in March, when spring growth begins, the first larvae emerge. In some areas of Arizona, active stages can be found the whole year round, even in winter, during periods of warmer weather. Larval development is most rapid at about 29°C (84.2°F) and ceases below 14°C (57.2°F). Under favorable conditions, there will be up to 12 generations per year.

Occurrence

Agricultural Importance

Scirtothrips citri is a serious pest of Citrus spp. in California and Arizona, USA. It is considered to be native to California, its primary host plant probably being Rhus laurina (Anacardiaceae), whereas citrus is an introduced crop. This means that S. citri must have undergone a remarkable host change. Citrus thrips is found in the USA (Arizona, California, Florida, Washington State) and in northern Mexico, and also in limited areas of China.
Reports from India remain to be confirmed.

Control

Integrated Crop Management

Scirtothrips citri is capable of resurgence after treatments that destroy populations of natural enemies, especially predaceous mites, which play an important role in the control of this pest.

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