Causal agent(s) and transmission
Thrips (Thrips tabaci) are small elongated insects of the order Hemiptera; they are about 1 mm long and the male is smaller than the female. The wings of the adult are slender, yellow to brown and the wing-edges carry cilia. The colour of the larvae is variable, whitish to orange, or even greenish-yellow and the head bears red eyes (photo 1).
In their feeding habit, the thrips larvae bite the leaves of numerous plants, including the potato; after feeding, the tested leaflets show numerous silvery-white spots, that correspond to the emptied cells. This symptom is usually associated with the presence of minute piles of black frass.
The thrips may also feed on the flower petals of the potato plant. They have 2 or 3 generations a year, depending on temperature, and in hot climates, they can pullulate.
Although thrips are widespread, significant damage to potatoes is rare, apart from the potential risk of virus transmission, notably the Tomato spotted wilt virus, which can also affect the potato.