The whereabouts of chilli thrips

"The invasive chilli thrips, Scirtothrips dorsalis Hood, has been in Texas and Florida for some time now, and it was hoped that the bug just didn’t like California. Regrettably, it has arrived." In the article below, James A. Bethke from the University of California, elaborates on the appearance, spreading and harm chilli thrips can cause to a variety of crops, as well as the ways growers can employ in combating them.

Scientists believe that chilli thrips originated either in Southeast Asia or in the Indian subcontinent, but it is now widely distributed. Chili thrips was first reported in Florida on October 2, 1991 with subsequent occurrences in 1994, 2004, 2005 and 2007 in various counties of Florida, and it was observed in southeastern Texas in 2005 on landscape roses and on peppers in retail centers. In August of 2015 chilli thrips were found at several residential properties in Orange County, California, and in October, it was detected on roses at the Los Angeles County Arboretum and Botanic Garden. Initially, the pest was rated “Q” and required regulatory action. Thereafter, it was determined that chilli thrips cannot be eradicated, and it is likely to become widespread in California. Recently, it was reduced to a “B” rated pest in California. The B rating still means that some counties may treat this pest as a significant pest, and that it may need local regulation.

Infestations of the invasive chilli thrips poses a number of challenges including:

Chilli thrips resemble many other thrips species
Unlike other thrips, pupae of chilli thrips are generally found on leaves, leaf litter, or on the axils of leaves, in curled leaves, or under the calyxes of flowers and fruits.
Chilli thrips damage resembles herbicide damage, micronutrient deficiency, or an aphid infestation.
Insecticide resistance is common.
Chilli thrips have been implicated in tospovirus transmission.

Chillithrips are known to infest a wide variety of host plants belonging to more than 200 plant species in 70 plant families, most of them ornamental. It can also attack many trees and tree fruits such as mango, apple, pears, citrusandlychee, and it can attack many field crops such as strawberries, peppers, eggplant, tomatoes, corn and cotton. Infested plants become stunted, and severe infestations can result in total defoliation of the host. Damage to roses includes distorted and elongated foliage, scarred flower buds, and brown, angular spots on the new growth of the roses and defoliation (fig. 1).

Fig. 1 (right). Chilli thrips defoliation of roses at the Winter Park Rose Garden in Florida. Photo: Lance S. Osborne, University of Florida.

On many hosts, chilli thrips also start feeding on the upper surface of leaves when the infestation is heavy (fig. 2– 3). Chilli thrips are principally a landscape pest and will damage many of the common landscape plants in California including Indian hawthorne, viburnum, shefflera, star jasmine, podocarpus, pittosporum, pyracantha and roses.

Fig. 2. Chilli thrips damage to terminal growth of shefflera. Photo: Lance S. Osborne, University of Florida.

If you are facing an infestation, it is recommended that you remove all infested foliage, bag it immediately and place it in the trash. Composting the foliage can lead to a greater level of infestation as the pests leave the infested foliage.

Research suggests thatfoliar sprays with insecticides containingacephate, imidacloprid, orspinosad are effective for pest control on ornamental landscape plants.Chillithrips are generally resistant to thepyrethroids such asbifenthrin, cyfluthrin andpermethrin, so they are not recommended for control, and are more damaging to beneficial insects.

Fig. 3. Chilli thrips damage to terminal growth of Indian hawthorn. Photo: Lance S. Osborne, University of Florida.

If you suspect that you have chilli thrips on your plants you are encouraged to seek expert help in identifying the pest. Identifying the pest will help pest control advisors and farm advisors make control recommendations.

Source: UC Nursery and Floriculture Alliance