Thrips are tiny insects (approximately 1-2 mm long) with unique wings. (Thrips is both the singular and the plural of this word.) Wings are narrow, long, and fringed with long hairs (and often without veins). Thrips can fly, but often weakly, and rely on long distance dispersal from the wind - often many miles. Some species of thrips in the Northeast are blown in from warmer overwintering locations, while others find a way to overwinter in cold temperatures. Thrips that injure ornamental trees and shrubs may cause injury to flowers, stippling and bleaching of foliage, leaf deformation - folding, rolling, or blistering, or the formation of callus tissue or galls (Johnson and Lyon, 1991). Distortion such as swelling, twisting, or cupping of plant parts can be caused by thrips feeding activity. Due to their small size, magnification is required to determine whether or not thrips are the cause of the plant damage. Different species of thrips that are significant in Massachusetts and New England are discussed in this Guide, such as the pear thrips (Taeniothrips inconsequens) and the privet thrips (Dendrothrips ornatus). Information about these species will be shared here, but for specifics about them, search for their individual sections in this Guide.
Pear thrips are tiny insects that are pests of deciduous trees. They were introduced into California from Europe in 1904. Adult pear thrips are slender, 1.5 mm long, and brownish-black in color with nearly veinless wings fringed with long hairs. In the Northeast, pear thrips adults become active in April and May and feed inside tender, newly developing flower and vegetative buds of their hosts. Winged females fly up to and enter buds. All adult pear thrips in North America are female and reproduce using parthenogenesis (asexually). After feeding, they will lay eggs in flower stems and leaf petioles, with small brown scars developing in the areas where eggs were laid. Eggs hatch, and both the pale white and translucent larvae (immatures) and adults feed on host plant foliage with piercing and rasping mouthparts which allow them to drink up host plant fluids that escape from the wounds they create. Tatterred, mottled, distorted, dwarfed foliage can result from pear thrips feeding. With very heavy populations, defoliation can sometimes occur. Feeding is typically complete by early June. Pupation occurs in the soil, and it is the pupal life stage that overwinters. A single generation is reported per year.
The life history and biology of the privet thrips is not completely understood. Adult females lay their eggs on host plant leaves late in the spring, with several generations per year possible through the summer. The number of generations on a single plant may depend upon the food quality of the plant for the thrips following so many generations of feeding. Immature thrips (larvae) are slender and wingless and found with magnification primarily on leaf undersides. Adults are also tiny, 1 mm in length, with wings. The larvae and adults feed and cause chlorosis on host plant leaves, which may be visible to the naked eye as a dusty/gray color. When populations are high, 20-30 privet thrips may be found per leaf. Adult privet thrips are active fliers. The privet thrips is non-native to North America, and was introduced. This insect is native to parts of Europe, Asia, and Russia.
The host plants utilized depend upon the species of thrips involved. Some are specialists on a single host, while others are generalists. Most hosts are deciduous.
Sugar maple is the primary host of the pear thrips in Massachusetts, but this species is also found on fruit trees and other maples. Feeding and egg laying in buds can cause severe damage. Tatterred, mottled, distorted, dwarfed foliage can result from pear thrips feeding, and in heavy population years, defoliation can also occur. Blisterlike scars on leaf veins and petioles may also develop. Although the damage from this insect can periodically be significant and noticeable, chemical management options are limited in their effectiveness because adult pear thrips emerge prior to host plant leaf-out in the spring. Adults enter newly developing buds to feed, which can protect them from contact insecticides. Abiotic conditions can also impact the relative damage caused by this insect. In springs where leaf expansion happens quickly, pear thrips typically cause less damage unless their population is extremely high. The longer the buds remain closed, the more damage may be possible from pear thrips feeding. Synchronization of adult emergence with bud expansion also increases the likelihood of damage from this insect. Maple trees, historically, that lose up to 2/3 of their leaves may be able to refoliate in a few weeks. Hosts that are otherwise healthy (not stressed by other factors) can often withstand repeated years of defoliation by pear thrips. However, consecutive years of heavy defoliation by this insect are not common. Tree vigor may be reduced, but hosts typically recover from the activity of this insect. Pear thrips will also feed on tree pollen.
Leaves and twigs of privet and other susceptible hosts are fed upon by the privet thrips. Attacked leaves will appear grayish in color, made up of chlorotic spots. Immature (nymphal) thrips are found on the underside of the foliage. Magnification is required to view the insect. Privet thrips are most often pests of nursery and greenhouse production.
Pear thrips damage can be monitored for in blooming hosts at the time of bloom. Tap blooms against a yellow surface to look for adult pear thrips. 5 adults (or any larvae) per 50 blooms sampled may indicate a need for treatment options in fruit production, but the threshold for ornamental host plants is likely higher. Because this insect has population outbreak years followed by relatively little damage, occasional outbreaks may be tolerated. Additionally, chemical management options for pear thrips in ornamental settings may be limited in their efficacy.
When monitoring for privet thrips, scout for graying or chlorotic leaves and visually inspect for long, tiny insects. Magnification will be required to help view them. Check leaf undersides. Visual scouting can occur regularly through the growing season in nursery production, and is aided by tapping symptomatic material over a white sheet of paper or placing blue or yellow sticky cards near plants. Search for the insects on paper or sticky cards.
No effective cultural management options for pear thrips have been noted.
For privet thrips, sanitation can help in certain circumstances to reduce thrips activity. This may be particularly helpful in nursery settings. Remove weeds, old planting materials and debris, and keep the area clean. Screening can also help exclude insects from greenhouses. Screens less than 0.88 mm. may be necessary to exclude thrips, but make sure the small screen size isn't impacting airflow quality in these settings.
Lecanicillium (previously Verticillium) lecanii, an entomopathogenic fungus that is naturally occuring, has been previously reported to attack pear thrips larvae removed from forest soils (Parker et al., 2011). Paecilomyces farinosus, Beauveria bassiana, Hirsutella spp., and Metarhizium anisopliae have been reported from various life stages of pear thrips in various locations (ex. tree canopy vs. soil) previously (Brownbridge et al., 1999). Depending upon geographic location, some papers discuss predators and parasitoids of pear thrips. However, the exact species present in New England and their overall impact on pear thrips populations may not be fully understood.
Predators, nematodes, and entomopathogenic fungi have been used to successfully manage certain species of thrips, particularly in greenhouse production. These methods are understood for western flower thrips and chilli thrips, but the efficacy of the different species of natural enemies available for use on privet thrips may not be currently fully understood.
Abamectin (NL)
Acephate (NL)
Acetamiprid (L)
Azadirachtin (immature) (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Bifenthrin+imidacloprid (L)
Carbaryl (L)
Chlorpyrifos (N)
Chromobacterium subtsugae (NL)
Clothianidin (NL)
Cyantraniliprole (NL)
Cyfluthrin (NL)
Dinotefuran (NL)
Fenpropathrin (NL)
Flonicamid+cyclaniliprole (N)
Tau-fluvalinate (N)
Gamma-cyhalothrin (L)
Isaria (paecilomyces) fumosoroseus (pupae) (NL)
Lambda-cyhalothrin (L)
Malathion (L)
Metarhizium anisopliae (robertii) (NL)
Neem oil (NL)
Pyrethrin+sulfur (NL)
Spinetoram+sulfoxaflor (N)
Spinosad (NL)
Some chemical management options for pear thrips cannot be used on sugar maples to be tapped for maple syrup production. As always, consult product labels for all instructions if the host plant being treated is to at all be used for food production. Chemical management of pear thrips is usually not possible or effective. For specific chemical management options of a certain thrips species, see the individual insect entry in this Guide for more information.
While imidacloprid products are often labelled for thrips management, and are registered for use in Massachusetts, this active ingredient may not be the best option for managing thrips. Unlike dinotefuran (another neonicotinoid), imidacloprid often does not provide satisfactory results when used to manage thrips. For example, some research suggests that imidacloprid causes insecticide resistance and resurgence in western flower thrips post application (Cao et al., 2019).
Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), dinotefuran (soil drench), Metarhizium anisopliae (robertii) (soil drench), and neem oil (soil drench).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
