Chilli thrips—Scirtothrips dorsalis
This exotic thrips (family Thripidae) was discovered in Los Angeles and Orange counties of Southern California in 2015. It was previously introduced into Hawaii and much of the Southern United States. Based on the environments of its occurrence elsewhere, chilli thrips is expected to spread throughout most of California.
Identification
Plant damage is generally the first indication that this tiny insect is present. The foliage discoloration and distortion caused by its feeding resembles plant damage caused by broadleaf herbicides (e.g., 2,4-D, dicamba), broad-spectrum herbicide (glyphosate), or another herbicide. Feeding damage of chilli thrips also resembles that of broad mite and other Tarsonemidae and aphids when they infest and distort shoot buds and tips.
Chilli thrips in the field cannot be identified to species. It resembles several other common thrips including avocado thrips and citrus thrips (both also Scirtothrips species, onion thrips, and western flower thrips. Confidently distinguishing chilli thrips requires expert preparation of specimens and examination of microscopic characters. When the tiny insects themselves are observed, a distinguishing characteristic is that unlike most other thrips they resemble, they do not drop as mature larvae to pupate on the ground. The prepupae and pupae of chilli thrips are generally found on leaves and in the axils of leaves, in curled leaves, or under the calyx (flower sepals or green whorl of leafy material on top of a fruit).
Adult chilli thrips have a mostly yellow body with pale brown wings and bands on top of the abdomen. They are about 1/20 inch long, about one-half the size of adults of the other thrips named above. Larvae are pale yellow to whitish, as are the immatures of many other thrips species.
Distinguishing characteristics of adult chilli thrips include antennae that are eight-segmented with segments I–II pale and III–VIII dark. The head is pale with three pairs of setae (tiny hairs) near the three, red eyespots (ocelli); one pair of which occur between the hind pair of ocelli. On top of the abdomen are three setae near the outer margin of each segment.
Life cycle
The life stages of thrips are egg, first and second instars (larvae or nymphs), prepupa (or propupa), pupa, and adult. Adult females insert their eggs inside plant tissue, commonly in buds and the underside of leaves. Each female lays about 60 to 200 eggs during her lifetime. The eggs hatch in 6 to 8 days. The 2 larval stages last about 6 to 10 days, during which they actively feed on hosts as do the adults. Mature larvae develop into prepupae for about 1 day then pupae for 2 to 3 days during which they do not feed.
Chilli thrips can complete 1 generation from egg to adult in 2 to 3 weeks when temperatures are warm. There are multiple generations per year.
Damage
Chilli thrips mainly feeds on buds and young leaves. However, all above ground parts of its host plants may be discolored or distorted by its feeding. Injured buds, fruits, and tender leaves commonly turn blackish to bronze in color. Damaged leaves curl and distort. Infested leaves and heavily infested plants can be atypically undersized. Feeding on buds may cause them to become brittle and drop. Some hosts, when heavily infested, prematurely drop many or all of their leaves.
Chilli thrips is principally a garden and landscape pest. It can infest more than 200 plant species in 70 plant families, most of them ornamentals. Hosts include aucuba, begonia, camellia, chrysanthemum, coleus, crape myrtle, English ivy, euonymus, geranium, Indian hawthorn, marigold, petunia, pittosporum, podocarpus, poinsettia, privet, pyracantha, rhododendron, rose, schefflera, star jasmine, viburnum, and zinnia.
Damage to roses includes brown, angular spots on new growth, distorted and elongated foliage, premature leaf drop, and scarred flower buds. Chilli thrips can also vector Tomato spotted wilt virus, which damages certain field crops and various herbaceous ornamentals, especially those in greenhouses and plant nurseries.
Chilli thrips can also attack certain food plants including blueberry, chili, eggplant, grape, pepper, strawberry, and tomato. But elsewhere in the United States it generally has not been a serious crop pest. There is more than one strain of chilli thrips and the hosts can differ depending on the strain.
Solutions
If you suspect that you have chilli thrips on your plants, it can be helpful to collect samples for expert identification. Seal infested plant parts in a zip-lock bag and take them for identification and advice to the local office of the county agricultural commissioner or University of California Cooperative Extension. Do not move suspected chilli thrips across county borders unless they are dead. If moving them across borders is needed to obtain an identification, to kill the thrips place the container with the them in a freezer overnight.
Chilli thrips are not easily controlled. Where they occur, use good sanitation to reduce thrips habitat. Remove weeds, plant debris, and old flowers and seal them in plastic bags for disposal. Do not compost debris from plants infested with chilli thrips as the insects can survive and move to infest hosts.
Obtain new plants from a quality, commercial supplier to reduce the likelihood of introducing thrips or other pests. If plants are grown in a greenhouse, screen openings with screen size of less than 1/32 inch (0.8 mm) to reduce thrips movement into the greenhouse. Because airflow is obstructed by screens of small pore sizes, the screened surface area must be increased to compensate.
Biological control agents available for purchase and application to manage thrips include entomopathogenic fungi (e.g., Beauveria bassiana), predaceous mites (e.g., Amblyseius and Neoseiulus species), and minute pirate bugs (Orius species). These natural enemies must be released early before thrips are abundant or their damage has occurred. Natural enemies will not control an existing high population of thrips.
To allow natural enemies to potentially be effective
- Avoid the application of broad-spectrum, persistent insecticides for all pests.
- Control ants because they attack natural enemies.
- Minimize dust that interferes with the activities of parasitoids and predators (e.g., periodically hose off shrubs).
- Plant flowering species (insectary plants) to provide nectar and pollen to feed adult natural enemies.
See Natural Enemy Releases for Biological Control of Crop Pests and Protecting Natural Enemies and Pollinators for more information.
No insecticides provide complete control of chilli thrips. Potentially effective insecticides include those with systemic or translaminar (entering the plant through the leaf surface) movement including acephate, imidacloprid, and spinosad. However insecticide resistance is common in chilli thrips. Chilli thrips are generally resistant to pyrethroids (e.g., bifenthrin, cyfluthrin, permethrin, and other "-thrin" insecticides); pyrethroids are not recommended for control.
When damage is noticed the thrips may no longer be present, because damage from thrips feeding does not become apparent until later when plant tissue has expanded and grown. It may be best to delay any insecticide application until the following growing season and then make the application when new growth appears on hosts that were damaged by thrips the previous growing season. For more general information and control advice see Pest Notes: Thrips.
For more information see Chilli Thrips; Chilli Thrips, Scirtothrips dorsalis Hood; Common Name: Chilli Thrips - Scientific Name: Scirtothrips dorsalis Hood (Insecta: Thysanoptera: Thripidae); National Pest Alert - Scirtothrips dorsalis Hood: Chilli Thrips, Castor Thrips, Assam Thrips, Yellow Tea Thrips, Strawberry Thrips (PDF); and Scirtothrips dorsalis Hood: (Chilli Thrips). |
Rose leaves reddened, undersized, and wrinkled by feeding of chilli thrips.
Indian hawthorn foliage blackened by feeding of chilli thrips.
Tip dieback of marigold from feeding of chilli thrips.
An adult chilli thrips, which resembles several other thrips species.
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