Thrips can be hard to spot without using magnification; without magnification they appear like dark slivers resembling lobsters up close.
Adult thrips insects are long and thin creatures ranging in color from yellowish-brown or black; their wings (if present) have narrow and fringed wings, while immature forms known as nymphs may or may not possess wings at all.
Damage
Thrips insects cause significant damage to flower, vegetable and fruit crops. Their piercing mouthparts penetrate plant surfaces to siphon away their juices – this process may distort parts of plants while leaving a grayish or silvery flecked appearance on their foliage. Thrips can also spread diseases among them.
Adult thrips (adult female) are straw-colored or black in color and feature two pairs of feathery wings; however, they can be difficult to detect without using a hand lens due to their ability to hide among leaves and flowers they infest. Hatching thrips (nymphs) appear translucent light-yellow in colour with short antennae and legs and experience rapid metamorphic growth via several metamorphic molts.
Adult and nymph thrips feed by rasping or puncturing bud, stem, and leaf tissues in order to gain entry and feed on them. This causes buds, flowers, fruits, foliage and fruits to deform or discolor significantly as well as producing unsightly brown or silvery speckles on its surface. In some instances it may even leave behind sticky residue that remains on plants over time.
Thrips also produce a dark fluid that can be seen dripping down petals or sepals of infested flowers, leading to discoloration or even raised bumpy spots with distinct yellow hues that appear as visible spots on petals and sepals. These spots may be round or irregularly-shaped.
Thrips can damage or deform fruit trees such as citrus and avocado trees, leading to reduced harvest yield and quality, scarred fruit, dark scarring on grapefruit skins, nectarines, apples and raspberries, light halos around grapefruit fruit as well as severely scarring blueberry shoot tips that reduces fruit production as well as possible disease outbreak.
Thrips do not feed on human blood; however, their bites may sting and be itchy. Thrips are drawn to moisture-laden areas; therefore they tend to attack people spending time outdoors near infested vegetation.
To protect against thrip bites, wear long sleeves and pants when gardening in areas prone to infestation by these bugs. It may also be beneficial to apply an insect repellent with 100% DEET content such as Genes Cream during peak times of thrip activity.
Life Cycle
Thrips thrives in hot environments. Many species of Thrips can be serious plant pests, causing mottling or other damage to leaves and flowers, particularly greenhouse plants. There are over 6,000 known Thrips species (order Thysanoptera).
Female thrips insects lay up to 100 eggs at one time, typically in flower buds or the tissue of leaves and stems. Eggs hatch within days in warmer climates or weeks to months in colder regions. Nymphal larvae feed by cutting into plant tissue with sharp mouthparts to extract sap. After two feeding nymphal stages, females move onto prepupal and pupal stages in close quarters on the ground or among plant debris before entering prepupal and pupal stages for pupation and pupation stages which gives them their distinctive feather-like appearance.
Once fully developed, thrips develop wings and depart the growing medium for safe places such as under plant debris or on the ground; over the course of one growing season there may be 12-15 generations of thrips.
Thrips may overwinter in decaying plant debris, bark or the ground before moving on to nearby gardens and greenhouses in spring to infest vegetables, flowering crops, fruit trees and ornamentals.
Thrips reproduce asexually, making their numbers rapidly grow in a garden or greenhouse that becomes infested. Natural enemies of thrips include lady beetles, parasitic wasps and lacewings which together with an application of Safer Brand NEEM Oil can serve as effective tools against infestation.
To reduce thrip populations, remove plant debris such as dead leaves and stems promptly after harvest or pruning to help prevent their eggs from overwintering in crops. However, in regions with cold winters thrips may overwinter as adults or immature forms in detritus or hollow stems and bark until spring arrives and they emerge to begin another generation of thrips.
Detection
Thrips’ piercing mouthparts cause damage that mimics fungal or viral infection. A telltale sign of an infestation with thrips is stippling or wrinkling of leaves, black excrement spots on leaves, buds and flowers, silvery varnish-like sheen on infested leaves and petals as well as ghost-spotting (small discolored spots surrounded by white haloes) on crop plants resulting in ghost-spotting (discolored spots with white haloes).
Thrips may be difficult to detect due to their small size; their damage often appears similar to nutritional or disease problems. When present, thrips prefer feeding on undersides of leaves and where leaves attach to stems as favorite places.
Adult western flower thrips (Frankliniella occidentalis) is easily identified by its dark body color and behavior: slow movements with hovering. Adults may leave behind sticky residue on leaves and petals. Furthermore, these insects often damage crops of tomatoes, cucumbers, and sweet peppers when present – often damaging crops which were otherwise intact.
As with aphids, many of the same methods employed to detect thrips also work effectively when it comes to detecting thrips – including the use of aphid catchers and beating trays. Though both species cause deformities in leaves and flowers alike, close inspection will reveal that thrips tend to have narrower leaf shapes – giving away its presence!
Sticky cards hung within crops to monitor thrips populations can also help. Blue sticky traps may be more effective at attracting thrips because their lighter backgrounds make the insects easier to spot.
Thrips pose a severe threat to greenhouse ornamentals, especially when they move indoors from outdoors and overwinter as bare-rooted or containerized stock. Thrips also pose dangers in outdoor vegetable and herb crops like tomatoes, cucurbits and squash in fields and high tunnels as they damage these crops as well as spread numerous plant diseases such as necrotic spot virus or impatiens necrotic spotted virus to edible and ornamental plants alike.
Treatment
Thrips can do serious damage to fruit trees, vegetable plants and ornamental blooms alike, spreading viral diseases that infected species such as roses, raspberries, tomatoes and onions are particularly susceptible to.
Thrips infestations may be hard to spot on the undersides of leaves and flowers, but can be easily seen when looking closely with a magnifying lens. Thrips damage is caused when these pests draw sap out from leaves and stems to feed on it, leaving mottled patches of leaves and flowers of affected plants behind; sometimes flower petals may even appear crookedly while buds may not open as promised by affected plants.
Early detection is key to mitigating thrip damage. Look out for signs such as stippling on plant leaves and flowers, and consider regularly spraying your plants with water jets to wash away any thrips that have settled onto their foliage and stems – this will help dislodge them before any permanent damage has taken place.
Integrative pest management is the best solution to combating thrips damage. Infestations should be minimized through tolerant gardening practices and selective use of chemical insecticides only when necessary; for example tolerating mild plant damage while using leaf sucking predator insects like minute pirate bugs, green lacewings and mites – which all effectively fight thrips – as well as regularly washing potted plants with water spray to dislodge any possible infestations of this pest.
Chemical controls include using insecticide sprays specifically labeled to kill thrips. You can find these products at most home and garden centers; be sure to read and adhere to all labels regarding dosage and application instructions. Avoid systemic insecticides like organophosphate acephate (Lilly Miller Ready-to-Use Systemic or Orthene), as these may be toxic to natural enemies as well as being groundwater contaminants.
Certain thrips can be very difficult to eradicate with chemical sprays, including citrus thrips which damage citrus fruit and blueberries, and Cuban laurel thrips which damage laurel fig terminals with darkened terminals. When applying multiple pesticides with similar IRAC codes in close succession, be wary as repeated applications could increase resistance in these species; while Mexican mint thrips and western citrus thrips can often be killed more easily with various insecticides.
