Greenhouse growers routinely scout for numerous insect pests. A recent addition to the scouting lineup is Thrips parvispinus, first discovered in a Florida greenhouse.
Dr. Lance Osborne, professor of entomology and associate center director at the University of Florida, discussed parvispinus during a recent AmericanHort webinar.
“It was first found in May of 2020,” said Osborne. “The grower brought samples and came back with positive ID for Thrips parvispinus – the first detection in continental U.S. It was feeding on Hoya anthurium in an Orange County greenhouse.”
The grower who found parvispinus on Hoya was importing plants from Indonesia and believes that is where the initial thrips colony originated. The pest was subsequently found on peppers, ficus and gardenia.
“In June 2022, it was found in residential landscape on Palm Beach Island,” said Osborne. “This represents a movement from greenhouses and protected production, where chemicals are regularly used, to a landscape.”
In early December 2022, parvispinus was found in vegetable fields. “This was particularly worrisome because growers didn’t recognize it,” said Osborne. “One grower lost a pepper crop estimated at $1.3 million.”
Parvispinus was later found on milkweed sold for butterfly gardens, and current literature lists 39 different plants as hosts. As the pest expands its range, new hosts will be identified.
Parvispinus is small, and growers will first see plant damage and not thrips. “It almost looks like broad mite damage in peppers – scars, stippled, silver flecking and distorted, curled leaves,” said Osborne.
Many growers are now aware of the thrips’ presence. “They’re not responding to chemicals,” he said. “Growers are seeing thrips damage on foliage they’ve never seen before.”
Osborne noted that the light-colored male parvispinus looks like a chili thrips, so for a grower having a new thrips problem, particularly on foliage, it’s likely parvispinus.
It’s important to properly identify thrips to manage the spread. Osborne reminded growers that federal law requires anyone who believes an invasive species is present in a location to report it to state regulatory officials.
In April 2023, the Florida Division of Plant Industry (DPI) sent a notice to all states regarding the presence of parvispinus on a list of imported plants infected with it. “To date, 36 nurseries and/or stock dealer locations have been placed under HOQ (hold order quarantine),” said Osborne. “To be released from the HOQ, nurseries and/or stock dealers can treat or destroy the infected host.” Florida is currently developing educational materials for growers to deal with parvispinus.
Parvispinus is moving around on ornamental and vegetable transplants. “So far it isn’t established in the landscape other than four counties,” said Osborne. “It’s polyphagous and shows marked preference for certain plant types. Detections are down – growers are identifying and managing the population.”
He said growers are using appropriate crop rotations to break the insects’ lifecycle and many growers are conducting on-farm efficacy trials.
Osborne said Florida is not the sole source of potentially infested plant material and urged growers to watch closely anything they bring to their nursery.
Dr. Sarah Jandricic, greenhouse floriculture IPM specialist in Ontario, Canada, said parvispinus is primarily a foliage feeder that leaves dark feeding scars similar to heavy broad mite damage.
“They also seem to target new growth,” she said. “All the new leaves and buds become brittle and stop growing. Parvispinus also feeds on flowers, and darker flowers show damage. We think this thrips is attracted to pollen and nectar inside the flowers.”
In Ontario, plants with the most severe response to parvispinus damage are trellising tropical plants with a single growing point such as mandevilla, dipladenia and Stephanotis. Jandricic is also seeing damage in other tropicals including gardenia, Hoya, schefflera, anthurium, ficus and hibiscus.
Greenhouse and outdoor peppers as well as chilis are also targets. Damage varies with plant growth stage and is especially severe when parvispinus attacks new leaves or vines.
Jandricic wants growers to be aware that parvispinus is tiny and difficult to see without a good 10x or 15x hand lens. Searching for this thrips on growing points is an impossible task because they’re tiny and move rapidly.
“Plant taps is what we recommend,”’ said Jandricic, “especially at the early vegetative stages. By the time you wait for flowers where the damage is obvious and the thrips will be inside the flower, it’s way too late.”
Plant taps (tapping the plant over a white sheet of paper or tray) are highly correlated with damage. “This thrips tends to be very patchy, even with a variety it likes,” said Jandricic. “It tends to aggregate in groups so it’s helpful to know its distribution in the crop so you can spot spray as needed.”
She added that targeting applications is important to allow some of the thrips population to remain susceptible to pesticide applications.
Growers can do plant taps over inexpensive white plastic trays to establish action thresholds and prevent unnecessary pesticide use. “If we found at least 10 thrips per five plants, or two thrips per plant,” said Jandricic, “that’s where we were seeing noticeable and concerning damage that was affecting growth.”
Watch for movement immediately after tapping a plant. Parvispinus looks like peat moss or other potting media debris and moves quickly.
“It’s important to standardize plant taps,” said Jandricic, who says taps are useful for estimating trends. “Tap the same number every week – that helps you track the population over time.” Count adults for the most accurate population estimates.
“Once plants become bigger and start to trellis and put on buds, we can tolerate 10 thrips per plant,” she said. “I don’t think we’re going to truly eradicate this pest from any facility – we’re going to have to live with certain numbers.”
Sticky cards can also be used for monitoring and trapping, and are most useful if plants are flowering. Insect numbers on cards correlate well with higher numbers in crops as well as noticeable damage. Sticky cards can help predict rises in thrips populations but are less effective in showing decreases.
For monitoring flowering plants, count adult thrips per flower. “They hide inside the trumpet flower and hide between overlapping petals,” said Jandricic. “Three or four adults per large flower signals a time for action.” However, counting adults on flowers isn’t as highly correlated to leaf damage as plant taps.
Jandricic summarized three main points when implementing a monitoring program: Monitor incoming plant material, especially if parvispinus outbreak is known in the location. Plant taps are useful; use cards to support treatment decisions. Make sure greenhouse employees know what to look for – both the pests themselves and signs of damage.
If possible, assign a dedicated person to scout weekly and graph the data. “Weekly because these thrips reproduce quickly,” said Jandricic. “It’s easy to get out of control if you skip monitoring for a week. If you used a standardized number of plants and card counts, graphing lets you visualize the data.”
More information about parvispinus, including identification, damage and plant tapping, is available at mrec.ifas.ufl.edu.
by Sally Colby
