Thrips, storm beasts, heat beasts !
Also known as "storm bugs" or "heat bugs", thrips are insects that can be seen in large numbers as soon as the hot weather returns. They wander around on your bare skin (face, arms, legs, etc) and can be particularly annoying. Thrips are harmless, of course, but as they are always in colonies, they quickly become exasperating. A black plague that comes back every year to spoil our naps. In this dossier, you'll find a range of answers and products to help you combat this insect, which is becoming more and more prevalent every year during the summer months.
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Scientific names : Frankliniella occidentalis, Heliothrips haemorrhoidalis, Thrips tabaci, Echinothrips americanus.
Order : Thysanoptera
Family : Thripidae
Adult size : 1 to 2 millimetres long
Location : Garden
Period : summer
What you need to know about thrips
With over 3,000 species, thrips form an order of their own: the thysanoptera. Each of these species is particularly fond of a particular type of plant, including rose thrips, peach thrips, pea thrips, onion thrips and cereal thrips.
Although some species are effective predatory allies in certain cases, most are crop pests. The Californian thrips, one of the most feared, arrived from across the Atlantic at the end of the 1980s. Very virulent in glasshouses, it also attacks many flowers in the garden, as well as tomatoes, cucumbers, aubergines, beans... and many fruit trees.
Thrips are really very small insects (1 or 2 millimetres long), discreet and polyphagous (their diet consists of feeding on a variety of foods), which makes them difficult to observe and control. They are generally light yellow, dark brown or black and have a striated body. They have elongated bodies and wings edged with long, fine bristles.
For a very long time, it was thought that these insects appeared in summer when the air became charged with static electricity, i.e. during stormier weather (hence their nickname, storm beetles). In fact, this is not the case: the appearance of these swarms of insects is due to the heat, but also to the harvest.
They like crops and, inevitably, your garden. They can number up to 2 million per square kilometre. No wonder they're everywhere. They sting plant organs to feed on the cell contents. The emptied cells then fill with air, resulting in silvery-grey spots or mottles.
They can be found in the air, travelling with the wind, or forming round swarms circling above our heads, ready to land on our sensitive, tanned skin. Silent, you can't hear them coming. They often end up returning to your home, as they take up residence on you. Thrips are usually females, and as they don't need males to reproduce, this explains their impressive numbers.
The development cycle of thrips
The metamorphosis of thrips is intermediate between incomplete and complete. Their life cycle usually comprises six stages of development: egg, larva (two stages), "pre-pupa" and "pupa" (pseudo-pupal stages) then adult.
- Eggs : kidney-shaped and relatively large compared to the size of the female.
- Larvae : resemble adults, but are smaller and apterous (wingless). They are often cream in colour.
- « Pre-pupae and pupae » : resemble adults. Pre-pupae have atrophied wings. Nymphs have more developed wings and long, backward-curved antennae. Organisms in these two stages do not feed and are generally immobile.
- Adults : They measure 1 to 2 mm in length and look like grains of rice. They are generally yellow, brown, black or white. Males are usually smaller than females. Thrips have little flight, but their two pairs of feathery wings allow them to be carried long distances by the wind. Some species are apterous. Thrips have sucking mouthparts.
Thrips can reproduce sexually, but mainly by parthenogenesis (asexually).
Females can lay 150 to 300 eggs during their short lifespan (30 to 45 days). In most species, the female inserts her eggs into plant tissue (leaves, flowers, petioles, tender stems, buds and fruit) using her ovipositor (egg-laying organ). Species without an ovipositor lay their eggs on the surface of the plant. Incubation lasts between 2 and 8 days. The young larva (1st larval stage) feeds for a short time before undergoing its first moult. At the end of the second larval stage, it stops feeding, drops to the ground and burrows in. It then transforms into a "pre-pupa", then a "pupa" before becoming an adult. Some species spend their entire development cycle on the host plant.
Depending on the species, thrips (often only females) may overwinter in adult or immature form in plant debris, under the bark of trees and shrubs, in the soil or between the scales of stored bulbs.
The length of the thrips life cycle varies according to species and temperature. The warmer the climate, the shorter the cycle. In general, the insect completes its cycle in 2 or 3 weeks. There are several generations per year.
Symptoms of thrips attack
Thrips often attack under cover, as they develop more rapidly when temperatures are warm and humidity low.
Their presence is often noticed by the damage they cause to plants. Thanks to their biting-sucking mouth cone, they empty the epidermal cells of their contents, filling them with air and causing silvery discolouration. When bitten, thrips inject saliva, which is toxic, leading to necrosis of the affected parts, particularly the flower petals. Their presence can also be seen in the tiny black dots that represent thrips droppings.
Thrips are also capable of transmitting viruses, and will develop whole necroses on adult plants.
In general, thrips prefer plants with fine petals, but there are many exceptions. Here are the plants they prefer :
- Indoor garden : Cyclamen, azalea, begonia, croton, ficus crassula, datura, dieffenbachia, fuchsia, hibiscus, orchid, yucca...
- Vegetable garden : garlic, asparagus, basil, carrot, cherry, cabbage, cucumber, strawberry, raspberry, bean, onion, leek, pear, apple, pepper, pea, potato, tomato, vine...
- In the ornamental garden : Aster, chrysanthemum, dahlia, gladiolus, daylily, iris, lily, snapdragon, carnation, pelargonium, petunia, peony, sweet pea, verbena, zinnia, birch, maple, hydrangea, rose, willow, lime, privet.
Factors favouring their presence :
- High temperatures
- Low humidity
- The presence of weeds
Thrips often settle in the hair and can quickly take hold, creating a permanent and very unpleasant irritation. On oiled skin or when you're sweating, they're particularly fond of settling, and you'll inevitably get an itch. As soon as you squash a few, they come back in large numbers.
In this case, the solution is to go home and take a shower. This will eradicate them immediately.
You can also protect yourself effectively against thrips with 3 of our products.
1 - One is to be applied to your skin : either our anti-insect lotion spray for the skin, or our anti-insect Roller. Made with eucalyptus citriodora, these body lotions will keep most insects at bay for several hours.
2 - The other is to be applied to your textiles : our Textile Insect Repellent. Containing geraniol, this spray will deter insects from clinging to your clothes for long hours.
Certain essential oils are powerful in protecting against thrips. These include essential oils of lavender, mint or eucalyptus and, of course, citronella. At the same time, you'll be protecting yourself from mosquitoes !
Everything you need to enjoy a sunny walk or family picnic without the worry of thrips.
How can I get rid of thrips in my home ?
Thrips are phytophagous insects, which means they feed on plants. So getting rid of them at home is fairly straightforward. If you take them all out, they won't be able to find any more food, so there's no point in keeping them there. Especially as some of them may be infested.
But that's not enough, as thrips seek tranquillity and warmth above all else. You need to find the source that attracts them, if it's not your plants. It could be a video screen (have you ever noticed them on your computer screen ?), a picture frame, etc. This is also the case if your wallpaper has been pasted with natural glue. Once you've found the source of the heat, try to limit it as much as possible.
How can I get rid of thrips in my garden ?
To check that they have attacked your plants, look under the leaves: if it's sticky to the touch or you have small black dots, thrips are present. These insects can be difficult to eradicate, and you'll need to be patient and conscientious in monitoring affected plants, but there are several solutions to help you combat thrips.
1. Mechanical control
As with red spider mites, prevention is based on a simple principle : keep moist !
Thrips do not develop when there is sufficient humidity. From May and throughout the summer, in hot, dry weather, regularly spraying the foliage of plants not susceptible to fungal diseases may be enough to prevent invasions. For indoor plants (with non-fluffy leaves) and greenhouse plants, spray the foliage throughout the year.
Another method : attracted by the colour blue, thrips can also be trapped by blue sticky plates. This method is widely used in glasshouses, but also works outdoors if the trap is well attached. Use one plate every five metres. Note that this solution has no effect on larvae.
2. Biological control
Biological control is an effective solution, but it will be necessary to determine precisely which species are present in order to find the right response. Not all insects are harmful to plants. On the contrary, some are our allies in the fight against pests!
So it's vital to think carefully when you come across an insect, and to learn to recognise auxiliary insects at all stages of their lives to avoid making errors of judgement.
The most common is the use of predatory mites such as Amblyseius swirskii, Amblydromalus limonicus and Neoseiulus cucumeris (predator of thrips eggs and larvae). These different beneficial insects should be used depending on the growing conditions, but "nursery" bags are still the most suitable technique indoors because they are easy to set up and last for several weeks. Orius predatory bugs and lacewing larvae can be used as alternatives, but are sometimes not very effective for home growers.
On the other hand, the use of nematodes (Steinernema feltiae), a natural predator of thrips, should only be used if the thrips species identified is actually completing part of its cycle in the substrate. This is not the case for all species. As for replacing the entire substrate, this is often excessive indoors, as it causes additional stress for the plant and has no effect if the insect in question does not enter the soil.
Ladybirds, green lacewings, Orius bugs and mites. You can use them in your garden to combat thrips without any counter-indications. A good idea might be to create insect hotels in your garden to attract them.
Certain auxiliary plants can also play an important role in controlling thrips. These include ornamental and common tobacco, marigold, campanula and sago grass.
3. Chemical control
Several of our insecticide products can help you in the fight against this insect.
Diatomaceous earth : This is an effective natural product for getting rid of a large number of pests, including thrips. It's very easy to use, just sprinkle it wherever thrips have settled. Repeat the operation regularly.
4J insecticide : As a last resort, you can treat with our 4J small insect insecticide (diluted to 1.5%). If you have a large number of plants to treat, use the same product in its concentrated form, with you doing the dilution (990 ml of water + 10 ml of pure 4J). Note that this product, based on plant pyrethrum, is short-lasting. It will therefore be effective for rapid curative action, but not for long-term curative action. As soon as the insect comes into contact with the 4J product, it will die instantly (pyrethrum's neurotoxic effect).
N.B.: As this product is not approved for use in gardens, we can only recommend it for use on houseplants, window boxes or window boxes. And do not use this product in a dilution higher than 1.5% or 2%. The foliage of your plants could otherwise burn under the effect of the pyrethrum.
Make your own natural insecticide : a natural insecticide made by mixing a decoction of garlic and black soap. Place 10 cloves of garlic in 5 litres of boiling water. Leave to infuse for at least half a day. Strain the mixture. Add 2 tablespoons of liquid black soap. Spray the plants with this mixture for three days. Repeat five days later.
Spray your plants once or twice a week for as many weeks as you need.