Citrus Thrips

Adult citrus thrips are small, orange-yellow insects with fringed wings. During spring and summer, females lay about 25 eggs in new leaf tissue, young fruit, or green twigs; in fall, overwintering eggs are laid mostly in the last growth flush of the season. Overwintered eggs hatch in March about the time of the new spring growth. First-instar larvae are very small, whereas second-instar larvae are about the size of adults, spindle-shaped, and wingless. They feed actively on tender leaves and fruit, especially under the sepals of young fruit. Third- and fourth-instar (propupa and pupa) thrips do not feed and complete development on the ground or in the crevices of trees. When adults emerge, they move actively around the tree foliage.

Citrus thrips do not develop below 58°F (14°C). They can produce 8 to 12 generations during the year if the weather is favorable.

When monitoring citrus thrips, you must be able to distinguish them from flower thrips, which feed on flower parts but do not damage citrus. Shortly after petal fall, immature flower thrips can be seen moving around young fruit, but they soon pupate and adults disperse to other plants, consequently they are only concentrated in citrus orchards for a short period in spring. For more information on distinguishing citrus thrips from other thrips, including all stages of citrus thrips and flower thrips, see UC ANR Publication 3303, Integrated Pest Management for Citrus, 3rd edition.

All varieties of citrus can be affected, however, citrus thrips is of greatest economic importance to San Joaquin navel oranges, satsuma mandarins, and all types of desert citrus. On fruit, the citrus thrips punctures epidermal cells, leaving scabby, grayish or silvery scars on the rind. Second-instar larvae do the most damage. They feed mainly at the calyx end under the sepals of young fruit and are larger than first instars. As the fruit grows, damaged rind tissue moves outward from beneath the sepals and presents as a conspicuous ring of scarred tissue, commonly called a ‘ring scar.'. A second type of scarring can occur around the stylar (bottom) end of the fruit. This scarring may be smoother than calyx-end scarring. Stylar-end scarring almost always occurs with calyx-end scarring and is a more common damage for mandarin varieties (true mandarins and their hybrids, satsumas, and clementines) than for sweet oranges. Thrips scarring may be severe enough to asymmetrically restrict fruit growth, causing a deformity in fruit shape. Fruit are most susceptible to scarring from petal fall until they are about 1.5 inch (3.7 cm) in diameter. Thrips damage is higher on fruit located on the outside canopy where fruit is also susceptible to wind damage and sunburn.

Citrus thrips numbers can vary greatly from year to year. Monitor to determine if a pesticide application is needed in a particular year. Navel oranges are more susceptible to damage than are Valencia oranges, which often do not require a pesticide application. Citrus thrips densities tend to be lower, and thrips scarring found much less frequently on the C. reticulata 'true' mandarins and their hybrids (Tango, W. Murcott Afourer and relatives) compared to oranges, clementines, and satsumas. Therefore, citrus thrips treatments for ‘true mandarins' and their hybrids are generally needed less often than oranges, clementines, and satsumas.

Treatment of young, nonbearing trees to protect foliage is not recommended except in severe cases. Although the citrus foliage is often heavily damaged by citrus thrips, healthy trees can withstand the damage and frequent pesticide applications can lead to insecticide resistance, making control of thrips on fruit more difficult in later years.

Citrus thrips is less of a problem in orchards that receive minimal broad-spectrum pesticide applications than in orchards that are treated with broad spectrum insecticides. Because of pesticide-induced hormoligosis (i.e. stimulation of thrips reproduction) and reduction of natural enemies, thrips numbers tend to increase after sprays with organophosphates, carbamates, pyrethroids, foliar neonicotinoids, and the miticide pyridaben (Nexter).

There are 7 to 8 generations of thrips per year and it is the 2^nd and 3^rd generation that attack the young fruit soon after petal fall.  Citrus thrips is less of a problem in cold, wet years because the cold delays thrips development and the wetness increases pupal mortality. In this situation, the 2^nd and 3^rd generations appear after the fruit has reached 1.5 cm in diameter and is less susceptible to damage.

A number of natural enemies attack citrus thrips, including the predaceous mite Euseius tularensis, spiders, lacewings, dustywings, and minute pirate bugs. Densities of greater than 0.5 predatory mites (E. tularensis, E. hibisci, E. stipulatus) per leaf assist with control of citrus thrips. They are also a very good "indicator" species, giving an indication of the level of general natural enemies present in an orchard.

In some years, when citrus thrips densities are excessively high, no amount of E. tularensis or other natural enemies in combination with selective pesticides can keep citrus thrips below an economic threshold.

Use biological control, sprays of the Entrust formulation of spinosad with an organically approved oil, or Veratran D applied with molasses or sugar bait in organically managed orchards.

Citrus thrips has a history of rapidly developing resistance to chemicals that are used repeatedly and frequently for its control. For example, resistance to dimethoate and formetanate hydrochloride (Carzol) developed in a number of citrus thrips populations in the San Joaquin and Coachella valleys in the 1980s; beta-cyfluthrin (Baythroid) resistance was documented in the 1990s, and spinetoram (Delegate) resistance appeared in the 2010s in San Joaquin Valley orchards. Although citrus thrips disperse considerably, citrus thrips resistance problems are generally localized. Thus, resistance problems are most likely to occur in groves where insecticides with the same mode of action are repeatedly applied to control citrus thrips.

With the limited number of pesticides available for control of citrus thrips now and in the foreseeable future, it is wise to monitor citrus thrips levels carefully and limit pesticide applications only to populations that are expected to cause significant levels of fruit scarring. It is also important to time and apply pesticides optimally so that reapplications are not required. Do not apply pesticides just to prevent foliar damage. Instead, focus on protecting young fruit.

The selective botanical insecticides sabadilla (Veratran D), spinosad (Success or Entrust), abamectin (Agri-Mek, etc.), spinetoram (Delegate), cyantraniliprole (Exirel) and the combination abamectin plus cyantraniliprole (Minecto Pro) are relatively nontoxic to beneficial insects and mites.  

The broad-spectrum organophosphate (dimethoate), carbamate (formetanate hydrochloride&–Carzol), and pyrethroids (beta-cyfluthrin&–Baythroid, fenpropathrin&–Danitol) insecticides are toxic and fairly persistent (greater than 5 weeks) against both beneficial mites and beneficial insects so they disrupt biological control.

Citrus thrips treatments are applied as outside coverage to the trees and this helps to allow natural enemies to survive in the interior and return to the outside of the tree as residues decline. Multiple applications of either selective- or broad-spectrum insecticides will significantly reduce populations of predatory mites. 

Check young fruit for immature thrips and monitor the undersurface of inside foliage (they avoid light) for predaceous mites. Monitor from petal fall until fruit is greater than 1.5 inches in diameter. For oranges, the monitoring time is about 6 to 8 weeks in spring. For lemons, monitor June through October.

Monitoring Fruit for Citrus Thrips

Select trees that are three to four rows in from the outside edge of the block. Sample 25 young fruit from each corner of the block for a total of 100 fruit. Take only one to two healthy, dark green fruit from outside, sunny branches of each tree. Look for thrips on the stem end of the fruit under the calyx. Count fruit as infested only if it has one or more wingless first-or second-instar nymphs (ignore pupae and adults). Record the total fruit infested with immature citrus thrips and calculate the percentage of infested fruit (example form). On very susceptible varieties, such as San Joaquin Valley navels, monitor fruit at least twice a week after petal fall, and continue monitoring as long as susceptible fruit is on the tree.

Monitoring Predatory Mites

Examine the underside of twenty 5-leaf terminals with fully expanded leaves from shady areas of the canopy (a total of 100 leaves) and count the number of adult predatory mites. Calculate and record the average number of predatory mites per leaf (example form). A minimum of 0.5 predatory mites per leaf is needed to assist with biological control of citrus thrips.

Treatment thresholds vary by growing region, cultivar, beneficial mite numbers, and the type of insecticide that will be applied. A significant factor affecting threshold levels is whether the orchard is sheltered from wind damage (lower threshold) or has a history of outside fruit scarring from seasonal winds (higher threshold). As fruit get larger, treatment thresholds go up. Less susceptible varieties such as Valencia oranges and Tango mandarins may not require monitoring or pesticide applications. For coastal lemons, orchards that have a history of outside fruit scarring from seasonal winds have a higher threshold for tolerance of thrips.

Sabadilla (Veratran D), spinetoram (Delegate), spinosad (Entrust, Success), abamectin (Agri-Mek), cyantraniliprole (Exirel), or premixes (Minecto Pro) are recommended to avoid severe mortality of natural enemies. When an application of sabadilla, spinetoram, spinosad, abamectin, or cyantraniliprole is planned, beneficial mite numbers are considered significant if you have at least 0.5 predators per leaf. Insecticides should be applied only when immature thrips are found on fruit, rather than on a calendar basis. In some years, cold weather slows thrips development and they are not present on the young fruit.

When monitoring indicates a pesticide application may be needed, it is essential to properly time and apply the pesticide in order to reduce the need for a second application, and thus reduce the long-term development of resistance. Apply the pesticide using outside coverage (OC) by reducing spray blower wind velocity. Ground application is more effective than air application. However, because of their smaller size, coastal lemon trees receive adequate control with an aerial application. 200 gallons per acre is more effective than lower or higher gallonage, except with the sugar or molasses bait treatments using sabadilla. Firm data on optimal gallonage with sugar baits are not available, but some growers believe that lower gallonage is more effective because the bait concentration is increased. Do not apply sabadilla and sugar bait just before or during periods of heavy dew, fog, or drizzle. Such weather conditions cause the sugar bait to separate from the toxin, rendering the treatment ineffective.

• Citrus thrips monitoring form (PDF)
• Photos of citrus thrips and western flower thrips