By Nate Royalty, Ph.D.
What do they look like?
Chilli thrips, Scirtothrips dorsalis (Hood), are pale-bodied, dark-winged invertebrates that reach a length of no more than 1/16 inch at maturity. Chilli thrips are smaller in size than western flower thrips and other commonly found thrips species, but it is nearly impossible to accurately differentiate chilli thrips from other species without the aid of a microscope. Distinguishing characteristics that can be observed under a microscope include an eight-segmented antenna, a pale head with three pair of ocellar setae and brown transverse lines on the ventral edges of the abdominal segments.
Host material and range
Although this pest is called the chilli thrips, it feeds on many other plants other than peppers. There are more than 100 recorded hosts from about 40 different plant families. Recently discovered in the United States in 2005 on landscape roses in Florida, this pest has since spread to eastern, northeastern and southern Texas. This introduction has been traced back to garden centers that import plants from out of state.
Infestations are frequently pinpointed by the distinctive feeding damage the insects create. Chilli thrips preferentially feed on newly developed leaves and buds, Using a “rasping” motion, chilli thrips wear away at these young buds and leaves, and then suck the sap from the inside of the plant.
Chilli thrip feeding turns plant leaves, buds and fruit bronze in color. Damaged leaves and buds become deformed, brittle and often curl and drop. Severe infestations stunt or dwarf plants.
It is crucial to check your ornamentals regularly for abnormal growth. During the initial stage of infestation, the undersides of plant leaves will turn shiny. If left untreated, leaves and buds will soon discolor and begin to curl.
Due to the recent introduction of chilli thrips into the United States, pest management programs are still being developed to effectively control this pest. However, preliminary tests have found that foliar insecticide sprays containing abamectin, acephate, spinosad or imidacloprid are effective for control on ornamentals. To date, soil-applied systemics have not been effective. Always follow label rates and instructions.
What can you do?
Plants with symptoms of chilli thrips damage should be closely examined for the presence of the pest. For species determination, collect and send five to 20 leaves from the symptomatic plant to a laboratory for identification. Place the sample into a resealable bag to prevent escape, add a dry piece of paper towel to avoid excessive moisture, and seal the bag. Label the sample with collection information, including city or town, county, date, and species of the host plant, as well as your name and contact information, and send to your local county extension agent.
Nate Royalty, Ph.D. is technical development manager <dash> insecticides, Bayer Environmental Science.