Thrips. General information

Thrips are small polyphagous insects. Their body length ranges from 0,5 to 15 mm, usually the size does not exceed 2 mm, but in the tropics you can find thrips up to 1 cm in size. They are distributed all over the world, but prefer a warm climate, so most of the species live in the tropics and subtropics. The order of thrips has about 6000 species and more than a hundred groups. The peculiar structure makes it easy to distinguish thrips from other insects.

Thrips have 5 stages of development:

• egg
• larva
• pronymph
• nymph
• imago

Sometimes a natural form of asexual reproduction without fertilization — parthenogenesis is exist.

Other common names for thrips include thunderflies, thunderbugs, storm flies, thunderblights, storm bugs, corn fleas, corn flies, corn lice, freckle bugs, harvest bugs, and physopods.

Thrips are sometimes called fringe-winged because of the specific structure of the aircraft: 2 pairs of narrow and long wings, fringed at the edges. The small number of veins on the wings makes the flight of the thrips peculiar and resembles rather a fluttering from one plant to another. Long flights are rare and not typical for all types.

The main difference between thrips by sex is based on the size of the individual. Males are usually smaller than females. There may also be differences in body colour, length, or lack of wings, but these differences manifest themselves differently in different species.

The basis of the nutrition of thrips are the juices and nectar of plants. The preferred habitat is the flowers of plants and the flowering of fruits, due to the availability of the food base. The sucking of juices and nectar from the flower of the plant leads to inhibition of development. Most of the species are recognized as pests in the agronomic sector. A considerable danger lies in the viruses carried by thrips on plants. Even though thrips are pollinators to some extent, and given the antiquity of the order, it is quite possible that they are among the first pollinators in the world, their role in pollination is insignificant. Thrips rarely fly from one plant to another and the amount of pollen transferred is incomparable with the harm caused.

It is quite difficult to detect thrips, given its modest size. One of the main ways of detection is the symptoms of the plant. The leaves or flowers of the plant begin to deform, the process of necrosis (tissue death) occurs, the leaves lose colour saturation, light or discoloured spots appear, which subsequently turn into holes. During the vital activity of thrips, due to excrement and egg laying, galls are formed on the leaves of plants, which weaken the plant and can cause its death. If the nutrition of thrips occurs at the point of growth, deformed ends of shoots will inevitably occur. It should also not be overlooked that thrips are carriers of dangerous viruses and are classified as quarantine objects.

How to deal with thrips?

Sticky traps

The use of sticky traps is not only a means of destruction, but also a way to monitor adult thrips. The disadvantage of this method is the lack of the possibility of destroying larvae. Of the advantages, it is worth noting that they are effectively used in trapping not only thrips, but also other phytophagous pests. Card and roll sticky traps are mainly used. Card traps for greenhouses with cucumbers are installed at a height of about 20 cm above the plant. In greenhouses with tomatoes at the level of the middle of the bush. The optimal amount in order to trap the pest as efficiently as possible is 1000-1300 pieces per hectare. The recommended number of roll sticky traps is 10-15 rolls per hectare. When choosing a roll trap, the colour will also matter if you want to save entomophages.

Pheromone traps

There are several types of pheromone traps, the action of which is based on one basic principle. The bait contains a pheromone to attract male and female phytophages, which allows you to lure them out of shelters. One of the options is a water pheromone trap. For monitoring purposes, a number of 10 pieces per 1 hectare is sufficient. Optimally arrange their circles, keeping a distance of at least 15 metres between them and 25 metres between the walls of the greenhouse to avoid attracting new insects from the outside.The plate is filled with water, to which a thin layer of oil is added. The pheromone traps adult males, which are caught on the surface of the liquid. It is also effective to use pheromone traps simultaneously with sticky ones on a similar principle.

Chemical agents

Chemical means of fighting thrips are used everywhere, but with the development of agronomy it is used less and less, in order to avoid harm to plants and useful insects. The disadvantages of this method are the complexity of the selection of the drug, since not every drug is able to penetrate into the leaf, which leads to the survival of the larvae. There is also a negative impact on the population of entomophages, and in the case of using stronger means, their death altogether.

Biological agents

Biological means of protection can be ranked as the most gentle and natural way of pest control. Among the natural enemies of thrips, predatory bugs Orius laevigatus, Orius majusculus, Orius niger, and predatory mites Amblyseius swirskii  and Amblyseius cucumeris are distinguished.