Updated: Sep 15, 2022
You think you have seen thrips on your plant? Do not waste time, act now before the damage is too great!
Thrips are one to two millimeter long insects. They are black, brown or yellow with 2 pairs of often folded feathered wings. Larvae, pale in color, resemble adults, but do not fly.
Unfortunately, there are several generations per year. So we can say that thrips are our sneaky enemies all year round. It is essential to keep an eye out for them detected as soon as possible to avoid irreversible damage to our precious plants. Unless there is a particularly virulent attack, it is rare for the plant to die, however, thrips can weaken it and transmit viral diseases. Thrips, like spider mites, thrive in hot, dry weather. When conditions are right, the development of thrips populations can be very rapid.
Individuals in the adult and larval stages feed by piercing plant tissue with their mouthparts and sucking the contents of plant cells. At the location of the dead cells, white, brown or silvery-gray spots form, with dark fecal matter left behind by the thrips.
Thrips control is very difficult because pupation (transformation of Diptera larvae into pupae nymphs) takes place in the soil and not on the plant. In most species, the female inserts the eggs inside the stem or leaf. Despite adequate vaporization with an appropriate product, there are always two generations that have not been affected and will take over as soon as your back is turned. It is therefore necessary to repeat the treatments every 5 to 7 days. And stay vigilant for the next three months.
Both adult and larval stages feed by piercing plant tissue with their mouthparts and sucking the contents of plant cells. At the location of the dead cells, white or brown spots are formed, to which dark feces left by the thrips are added.
Prevention: Chemical, biological and mechanical control
-Prevention is based on a simple principle: humidify! Thrips generally grow much less when there is sufficient humidity!
- Neem oil vaporization: Neem oil is biodegradable, does not create resistance in insects and is very economical. The Neem tree, also called neem tree (Melia azadirachta or Azadirachta indica), is a very widespread tree in India. It is found in all hot climates. Its seeds are pressed to give a strong-smelling oil, the main active substance of which is azadirachtin. Neem oil is also a natural insecticide to protect plants from pest insects. It can be used throughout the growing season. How does it work? Neem oil, and more specifically azadirachtin, is effective on a large number of insects and mites, including caterpillars, some aphids, some thrips, mites including red spider mites, scale insects, and many Diptera and Hymenoptera.
It acts at several levels of the physiology of these insects:
• It paralyzes the digestive tract, ie the insects can no longer digest what they have ingested: they stop feeding and die.
• It blocks molting in the larvae, which never reach the adult stage and die.
• It inhibits sexual reproduction, by blocking couplings.
The effects of Neem oil on the parasites are not immediate, you have to wait 2 or 3 days to see the death of the insects or their escape!
*You can make your own recipe by introducing 5 to 10 ml (1-2 tsp) of pure Neem oil in a spray bottle and filling with lukewarm water to reach approximately 100 ml. Shake well before use to disperse the oil in water, then spray on plants.
You can treat your plants with insecticidal soap. Do not forget to repeat this operation every week for a period of up to three consecutive months. Since thrips have developed resistance to most registered pesticides, biological control now remains the primary strategy for thrips control.
Biological control agents include predatory mites, such as:
• Neoseiulus (= Amblyseius) cucumeris;
• Amblyseius swirskii;
• Iphesius (= Amblyseius) degenerates;
• Stratiolaelaps scimitus (= Hypoaspis miles);
• Gaeolaelaps gillespiei;
• Gaeolaelaps aculeifer (= Hypoaspis aculeifer);
• Pirate bugs (Orius insidiosus);
• Nematodes (Steinernema feltiae);
• The entomopathogenic fungus Beauveria bassiana.
N.Ccucumeris and A. Swirskii are the most widely used predatory mites. They look a lot alike. These mites control thrips by feeding on first instar larvae. A. Swirskii can also feed, to a lesser extent, on second instar thrips. You have to wait a certain number of weeks before seeing the effects of their predation and you cannot hope for the total elimination of thrips populations. N. Cucumeris takes about 10 days to complete its life cycle at 20°C and about 6 days at 25°C. A. Swirskii needs more heat for its development than N. Cucumeris and therefore gives better results under summer conditions. Its biological cycle has the same duration as that of N. Cucumeris, but it depends on the number and type of prey available.
The mechanical fight:
Another tip to know: There are self-adhesive traps to catch adult thrips. Usually these sticky traps are yellow, but it turns out that thrips are more attracted to blue, so a blue sticky was developed for this purpose! Traps should be placed very close to infested plants because, despite its wings, thrips are not prone to fly very far.
Visual and manual inspection is really important in our daily routine. It allows us to detect unwanted insects as well as any physical changes as soon as possible. We look at the top and bottom of the leaves, the stems and the soil. Particularly check new leaves, flower buds and new flowers which are most likely to be attacked by an undesirable insect. It is almost certain that an infestation starts with an insect or egg on a leaf! So, if during this inspection we eliminate this leaf with the insect that is there, there is no risk that the whole plant will be infested by the eggs or young of the first insect!
Interesting fact: did you know that thrips in nature play an important role in pollination?
Thrips pollinate many plant species, alone or in conjunction with other vectors (animals, wind). An adult thrips can carry up to several hundred pollen grains. They can move from one plant to another, or even be carried by the wind to conspecific plants (of the same species) far away. Some species are very specific to particular host flowers (inflorescences, flowers, sporangiate strobili or "cones"). In contrast, Thrips setipennis in eastern Australia is the only insect capable of entering the tightly closed flowers of Wilkiea huegeliana and thus effecting pollination, but this thrips also breeds in the flowers of many other plants ( Williams et al.2001).
Thrips can detect color and odor in flight and actively fly short distances in response to these cues and possibly other cues such as shape. Localization of hosts over long distances is achieved using a combination of active and passive dispersal on wind currents. So-called "rewards" associated with thrips pollination include: pollen, nectar, and possibly other epidermal cell contents, brood sites, warmth, protection, and mating opportunities. Thrips can manipulate pollen of different sizes, sculptures, and textures for food, and female thrips will produce more eggs after a meal of pollen. The pollen grains that thrips inadvertently carry are relatively small, dry or slightly sticky. They must adapt the shape and size of the grains to avoid losing them in flight!
Good luck in your fight! Be persistent in your choice of intervention, because they have no mercy!