Southern California is a hub for nursery and floriculture production in the United States, with a mild climate that allows many kinds of plants and flowers to grow. Unfortunately, this also makes the area vulnerable to a wide range of invasive pest species, among them, Thrips parvispinus. 

Thrips parvispinus is a small thrips species that feeds on numerous ornamentals and even food crops. Their main hosts include Dipladenias, Mandevillas, Gardenias, Anthuriums, and peppers of all kinds. Adults and larvae feed on flowers and young leaves causing scarring, distortions, and sometimes even killing the plant. This damage combined with a rapid generation time makes T. parvipinus a serious pest of ornamentals and peppers. 

While Thrips parvispinus is not known to be present in California, it is already established in Florida, Hawaii, and Ontario. However T. parvispinus can be present in an area for a while and remain undetected. As an example, after T. parvipsinus was officially identified as present in Florida researchers visited commercial garden centers across the state and sampled known T. parvispinus hosts. They found T. parvispinus in almost every garden center they checked and in many counties where it was not known to be present, indicating T. parvispinus was much more widespread than previously thought and had likely been in the state for a while before being officially detected. In short, T. parvispinus can arrive undetected and become established before growers are aware of the threat. 

I was aware that T. parvispinus posed a threat to agriculture in California, and I knew about the work that had been done previously in Florida. I was also aware that it was likely only a matter of time before T. parvispinus showed up in Southern California especially given how many plants are shipped into the region from places like Florida and Hawaii. With all this in mind, I hired two students to help me replicate the work researchers had done in Florida: We would visit commercial garden centers around San Diego County and check known host plants to see if T. parvispinus had entered California undetected. 

At the very first garden center we visited, we found T. parvispinus present on multiple host plants. We continued our survey over the next month and ended up finding T. parvispinus at almost every store we visited throughout San Diego County, and even up into Orange County. 

Working with the Pest Exclusion team at San Diego County Ag Weights and Measures, we identified a single grower who almost all the plants were coming from. The plants were placed on hold, several thousand were destroyed both at the grower’s operation and at garden centers, and the sale of host plants from the grower was temporarily blocked. 

After all of this, we checked host plants in garden centers again, and while we did see plants that showed signs of T. parvispinus feeding, we have not yet found any new T. parvispinus the second time around. We plan on visiting garden centers a third time as the weather warms and are collaborating with colleagues in Ventura and Santa Barbara to also check garden centers in those counties.

Additionally, working with the UC Master Gardeners from San Diego to Santa Barbara, we checked host plants out in the landscape to see if T. parvispinus was present in landscaping or in gardens. So far, we have found very few host plants: Despite being common in garden centers not many people seem to be planting Dipladenias, Mandevillas, or Gardenias. On the host plants we have found, there have been no T. parvispinus and no signs of their characteristic feeding damage. 

From our findings, it seems possible that we caught this T. parvispinus outbreak early enough to prevent it from spreading to other nurseries or to landscape plants. On the other hand, there is still a good chance T. parvispinus has already become established in Southern California judging by the scale and spread of infested plants in garden centers.  We even saw some shoppers leaving with what looked to be infested plants during our first visits to garden centers. We’ll have a much better idea if T. parvispinus is here to stay or not as we continue our surveys this spring and summer.  

With all that in mind, vigilance is key especially in Southern California. Growers, landscape managers, and residents should keep an eye out for T. parvispinus and recognize the damage it causes on common hosts. 

After T. parvispinus feeding, Dipladenias and Mandevillas will develop notched leaves, have stunted growing terminals, and show signs of scarring on leaves and flowers. Gardenias will have scarred and stunted new leaves with some distortions. Pepper leaves will become distorted and will take on a crinkled appearance with some scarring also visible.
 

While it will be difficult to positively ID T. parvispinus on your own, watch for small, dark, and active thrips. Adult female T. parvispinus are smaller and darker than adult females of common species like Western Flower Thrips. If you see one under magnification, adult female T. parvispinus have a brownish head and thorax with a dark abdomen and wings that appear light close to the body and darker further out. 

Keep an eye out for this damaging invasive thrips species and reach out to me or another UC Cooperative Extension advisor if you have questions or think you have found it! Vigilance on all our parts will help keep this damaging pest in check and hopefully prevent it from establishing in California. 

Eric Middleton is an IPM Advisor with the University of California Statewide IPM Program and Cooperative Extension, serving San Diego, Orange, and Los Angeles Counties. He can be reached at egmiddleton@ucanr.edu.