Insect guide > Thrips


Thrips(Order Physopoda.)
The very minute insects known as "thrips" belong to this order, which is a very well differentiated group and has apparently no very close relatives among the insects. It is unfortunate that in this country the name thrips has been applied largely by vine-growers to some of the little leaf-hoppers of the family Jassidae (q. v.), but the name was long preoccupied, both popularly and scientifically, by the physopod insects, which, by the way, are also sometimes called Thysanoptera. They are very minute, slender insects, with four wings which are also very slender and very short, perfectly transparent and practically without veins. They are fringed, however, with long delicate hairs and lie along the back of the abdomen when at rest. The metamorphosis is incomplete and the mouth-parts are of very curious shape, but probably function in sucking.
They are really intermediate between true biting and true sucking mouth-parts. A striking peculiarity of the mouth-parts is that they frequently differ on the two sides. In other words, they are asymmetrical. Although the metamorphosis is incomplete, what may be called the pupa is not active. The larvae, however, are not in the least worm-like and resemble the adults, except for the lack of wings. The feet are curiously constructed and have a little bladder-like vesicle at the tip, from which fact the name of the order was derived.

The thrips are found in the greatest numbers in the flowers of flowering plants and there can be little doubt that they do considerable damage by injury to the essential organs of flowers.

Although the statement has been made that they sometimes feed upon other insects, the evidence is not good. An interesting form in this country lives in the sheaths of timothy grass and sometimes causes the dying of the heads of the grass. Sometimes they are found under bark and in fungi, and in Australia some of them form galls on the leaves of acacias. In the United States, however, they are most abundantly found in flowers and frequently in the heads of wheat. In greenhouses thrips are especially noticeable. Dracaenas are said to suffer especially from their attacks. They are commonly found on chrysanthemums, on hydrangias, in orange blossoms, and many other flowers.

Probably the most injurious species in this country, however, is the so-called onion thrips which causes the disease known as the white blast of onions. The same species is found on leaves of cabbage and cauliflower, squash, turnips, nasturtiums, and many other plants. It is also found in Europe where it occurs on tobacco, as well as upon garden plants. It is known as Thrips tabaci Lind.

It does not seem to be generally known that parthenogensis has been found to occur with thrips. Less than one hundred and fifty species are known, but almost no one has taken the trouble to collect these little creatures in out-of-the-way places, and it is reasonable to suppose that the order will be found to be quite numerous in species.