Thrips

Thysanoptera

Thrips, Thunderflies, Thunderbugs, Storm Flies, Thunderblights, Storm Bugs, Corn Fleas, Corn Flies, Corn Lice, Freckle Bugs, Harvest Bugs, Physopods

Thrips (Thysanoptera) - Guelph, Ontario 02 by Ryan Hodnett (CC BY-SA 4.0)
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A yellow flower in the snow
Thrips (Thysanoptera) - Guelph, Ontario 02 by Ryan Hodnett (CC BY-SA 4.0)
1 of 4
Thrips, often called thunderflies, make up their very own insect Order. They're not overly diverse, many species look alike and can be challenging to separate. They're tiny (1-2mm), slender, with elongated wings that are held flat against the body while at rest. They're vegetarians, so some can be pests of garden plants. They suck the sap from leaves or flowers, sometimes causing discolouration and deformed growth. Flower thrips are readily attracted to bright floral colours. Sometimes they mistake brightly dressed people for flowers so that they may give you a tiny nip.

Traits

Thrips feeding can cause deformed growth of leaves and flowers.

Appearance

Thrips are often seen in groups; they're seldom solitary! They can vary from black, brown, white and cream. There's little diversity in terms of appearance. They are small, narrow-bodied insects (2mm). They 'jump' away or fly when disturbed. They possess narrow, elongated wings fringed with hairs. These are held flat against the body when the insect is at rest. The immature thrips (called nymphs) are generally paler than the adult, mostly looking creamy-yellow. They're wingless, sometimes bearing undeveloped wing buds. Many nymphal stages spend most of their lives developing in the soil.

Symptoms

May produce mottling in leaves. Dull colouration to leaves, developing to silvery-white discolouration on the upper leaf surface. Discoloured areas often have small black spots of excrement from the thrips. Mottled flowers, white flecking where pigment has been lost. A heavy infestation can prevent flowers from opening. Distorted growth if present at growing tips or flower buds. Tiny, black elongate insects on undersides of leaves.

Activity

Diurnal

Personality

Order

Thysanoptera

Metamorphosis

Incomplete

Distribution

Worldwide

Biological treatment

Thrips infestations are easily manageable with good housekeeping. Likewise, plants should be regularly inspected in areas where the leaves meet the stems, as these areas tend to be where females lay eggs. Green mulch tends to attract Thrips, so should be avoided if your plant has had a previous thrip infestation. Sticky traps can be used as a cheap and easy method for light infestations. They're also an effective means of monitoring infestations. Thrips seem to be more attracted to the colour blue as opposed to yellow. Gently spraying plants down with a hose to remove any eggs and insects will help to remove pests outdoors. Due to their small, slender builds, thrips can be difficult to control using biocontrol. There are some species of predatory mite which can be useful in greenhouse conditions, such as Amblyseius species, Hypoaspis species and Macrocheles robustulus (Mighty Mite). Pesticides should not be used in conjunction with biocontrol. Ladybugs and lacewing are key predators of thrips and work exceptionally well in a greenhouse setting. You can catch ladybirds and release them into your greenhouse or garden area. You can attract beneficial insects to the garden by keeping some areas wild while planting a good selection of flowering plants. The addition of insect habitats to your garden (e.g. log piles, bug boxes, hotels, flower baskets and herb gardens) can help make gardens more attractive to predatory insects.

Chemical treatment

Due to their small sizes and rapid rates of reproduction, thrips can develop resistance to an insecticide incredibly quickly. Chemical spray instructions must be carefully read if plants are intended for consumption. If sought, sprays may need to be applied twice to ensure all development stages are targeted. Focusing sprays where the leaves meet the stems can be effective as this is where thrips tend to lay eggs. Organic sprays are available for use, usually containing some form of pyrethrum or natural oil. It coats the plants and sticks to any insects which come into contact with it. These sprays are much more environmentally benign, as opposed to synthetic compounds. Persistent insecticides containing lambda-cyhalothrin, deltamethrin, and cypermethrin are more persistent, so should only require an application. These sorts of chemicals should only ever be used when an infestation is considered heavy; they shouldn't be sprayed on any plant while in its flower.

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