All species of thrips employ the same strategy: they prick the upper cells of a plant and suck them dry. The drained cells then fill with air and take on a silvery color. Adjacent cells may also die off. But the damage symptoms also differ by thrips species and by crop. And that's not all: thrips can also cause a loss of vigor and production. So put, the consequences can quickly get out of hand.
Thrips are not picky, with most thrips species targeting many plant species. However, there is a difference in where the thrips congregate and feed on the plant, as each type of thrips has its own 'favourite spot.' Western flower thrips, for example, prefer flower buds and growth points, which don't grow or become deformed if damaged in their early stages. When the western flower thrips prick petals, this often leads to discolored spots and dots. These patches are brown on white roses and white on red roses. Early damage to a cucumber fruit causes it to grow curved. On sweet peppers, the western flower thrips causes light brown stripes on the fruit. The onion thrips can also cause deformed fruits.
But the leaves are fair game, too, with many species of thrips attacking this part of the crop. This can be a major problem, especially for ornamental plants. Silver spots appear on the leaves, and large infestations may also lead to yellowing and occasionally even leaf fall. Moreover, the excrement of thrips causes black spots, which naturally also affect the ornamental value.
In leeks, thrips mainly cause cosmetic damage: the yield does not suffer and consumers can easily remove affected leaves. Despite this, affected leeks usually command a lower price due to their less attractive appearance.
A general side effect of thrips infestation is reduced vigor of the crop. But that's no surprise, given that the insects are constantly sucking away nutrients. The plant tries to repair the damage and produces antibodies against the attackers. All this costs a lot of energy, which comes at the expense of the yield. Compare it to a developing flu virus in your own body: it takes so much energy to control the pathogens that you are usually less productive.