Thrips Control and Intraguild Predation
Are you familiar with different species of Thrips?
Have you ever wondered if beneficial bugs are compatible?
Will releasing more than one biocontrol agent at a time lead to them eating each other?
PHOTO - Orius insidiosus on dianthus kahori, Photo by Alec Blume
This week we are going over various species of thrips, identification, and control.
The most common species of Thrips in North America are Western Flower Thrips (Frankliniella occidentalis) a pest found in both vegetable and ornamental crops, Onion Thrips (Thrips tabaci) usually a problem only in vegetable crops, and Chili Thrips (Scirtothrips dorsalis) which is a significant global pest of ornamental, vegetable, and fruit crops. While these three species of Thrips are pests that damage your crop, it is important to note that there are predatory Thrips, such as the Sixspotted Thrips, Banded Thrips, and Franklinothrips. These species will feed on pests and actually help your crops! Lowering pesticide usage through using biocontrol agents can boost these beneficial populations.
PHOTO - Adult Thrips tabaci female
Thrips Damage, Life Cycle, and Control
Thrips have a feeding damage pattern that typically leaves behind silvery splotches with darker spots which are known as frass (excrement). While this may appear on some plants, their damage can vary depending on plant species. Their eggs are also laid inside leaf tissue which gives their offspring a perfect place to emerge and begin feeding. As populations increase, damage will become more noticeable and will bring on further stress symptoms to the plant. Some of the more economic impacts of this pest include the distortion and stunted growth of fruit and leaves that is a result of the plant being robbed of its precious water and nutrients. This damage will significantly lower your crops value. On tomatoes, thrips feeding can cause “ghost rings” on the fruit. Further, thrips are also known to be viral vectors meaning their feeding can spread viruses from plant to plant. One example of this is Western Flower Thrips transmitting Tomato Spotted Wilt Virus, which is lethal to tomatoes and some ornamentals.
Each of these three species of thrips have similar life cycles. Eggs are laid in leaf tissue and hatch after 5-8 days. Female thrips can lay 6-10 eggs per day over their life span of 4-5 weeks. Just one female can lay upwards of 200 eggs in her lifetime. The nymphs feed on plant tissue for 8-10 days, then drop to the ground to complete development in protected sites in the soil. The prepupa and pupa stages are both non-feeding stages while in their underground development stage. When fully grown adults emerge, they fly to upper parts of plants to continue feeding and laying eggs after a day or two.
As with any pest, a combination of biological and cultural controls, compatible chemicals and preventative measures gives the best results. These biological controls described below are compatible and can be used together.
Amblyseius cucumeris/Amblyseius swirskii – These predatory mites feed on immature stages of thrips. The cheaper, slow release sachets are a great option for long term coverage and are easy to hook on every plant. A. cucumeris will feed on both Western Flower Thrips and Onion Thrips. A. swirskii may be a good option for Chili thrips. If you need help determining the best choice of predator mite for your particular growing environment, please contact us at Sound Horticulture. We would be happy to help!
Orius insidiosus – This tiny pirate bug feeds on pollen and all mobile stages of thrips. When Orius is combined with A. cucumeris, relatively low release rates have given excellent control. One of best feature of this predator is that it will feed on all life stages of thrips, including adults! For complete control it is important to use a predator that can eat immature and adult stages. They also have small wings and can fly short distances, giving them a solid chance at thoroughly exploring your canopy in search of food. Orius will feed on WFT, Onion, or Chili thrips.
Stratiolaelaps scimitus – This soil-dwelling predatory mite feeds on the immature stages of thrips in the soil or growing media. Strats alone cannot control thrips infestations, but it contributes to the effectiveness of biological control when used other predators. This predator will also feed on fungus gnat larvae, which do actively feed on roots.
Monitoring and scouting are also important in controlling this pest. Many growers will be familiar with the yellow sticky trap. Thrips happen to be more attracted specifically to blue sticky traps. In areas where Thrips are the main pest concern, blue sticky traps should be used. Yellow sticky traps may make counting and identifying pests more accurate and will also attract other flying pests such as fungus gnats, winged aphids, as well as thrips. Tracking pest levels stuck to the cards on a regular basis can give you an idea if pest populations are increasing or declining. They can also give you an idea of where these pests are more present in your space. This can help you determine where your biocontrols can be most useful. Here at Sound Horticulture, we offer both of these sticky traps and have plenty available for your growing space!
PHOTO - Life cycle of the Western Flower Thrips. Note the soil inhabiting prepupa and pupa stages. Using soil predators can help eliminate thrips from becoming full grown adults. This can often be overlooked as a method of thrips control.
Thrips Identification
It is imperative to identify the species of thrips that are causing damage to your plants. Certain thrips species can put a halt on plant exportation (Chili thrips) and some methods of control may differ for some species. Onion thrips and chrysanthemum thrips are both susceptible to spinosad containing products while Western Flower Thrips are not. Echinothrips is a species that does not pupate in the soil so Stratiolaelaps will not be as effective for control.
Check out this link for more information on identification. This key was developed by Dr. Sarah Jandricic, currently the Greenhouse Floriculture IPM Specialist for the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA).
What is Intraguild Predation?
Intraguild Predation (IGP) occurs when one biological control agent feeds on another biological control agent.
Predators that feed on the same prey are known as a guild. This occurrence can lead to a negative effect on the impact of the biocontrols. “Through intense intraguild predation, predators can reduce the impact of other guild members such as the parasitoids that are released to control the aphid population, and trigger or worsen prey outbreaks indirectly and potentially allow for an increase in the amount of aphid damage to the plants.” (Rosenheim et al., 1993; Snyder and Ives, 2001, 2003)
Some examples of observed IGP are:
–Neoseiulus californius will feed on Phytosieulus persimilis while they both share the same prey of Two Spotted Spider mites
–Amblyseius swirskii will prey upon the larvae of the aphid predatory midge Aphidoletes aphidimyza and will also feed on the eggs, larvae and nymphs of P. persimilis
–Orius insidiosus will feed on sweet potato whitefly, Bemisia tabaci, nymphs that have been parasitized by the parasitoid Encarsia formosa
We are aware of these intraguild interactions and will cater your orders to meet your company’s needs considering growing environment and achieving comprehensive control while avoiding IGP.
Orius insidiosus
Also known as Minute Pirate Bug, Orius insidiosus are generalist predators that consume pollen and a variety of species of small, soft-bodied insects including mites, aphids, and small caterpillars. They are most effective for pests with life stages that inhabit flowers (such as flower thrips), as adults are attracted to, and often found in flowers. All stages of Orius move very quickly. The adults are good flyers and move efficiently throughout a greenhouse to locate prey.
Application rate: 0.5 – 1 per 10 square feet of canopy
Amblyseius cucumeris or swirskii
A. cucumeris prefers to feed on first instar thrips larvae but will also feed on second instars. Being a generalist, it is also capable of feeding on other mites such as broad mites, the eggs of two-spotted spider mites, and pollen in the absence of prey. It works well on low to moderate infestations of thrips and as a preventative measure but should be used with other thrips predators such as Orius, or A. swirskii for improved control of serious infestations. Apply with Stratiolaelaps scimitus (formerly called Hypoaspis miles) to control thrips pupae
in the growth media.
Application rate: 25-40 mites per sq ft depending on pest severity. If dealing with broad or russet mites, 60 per sq ft.
Dalotia coriaria
Atheta coriaria or Rove beetle (Dalotia coriaria), formerly known as Atheta coriaria, is a native species of a soil-dwelling rove beetle which feeds on small insects and mites. Both adults and larvae are active aggressive predators and are attracted to decomposing plant or animal material and algae, where their hosts are found. While they are beetles, they do not necessarily look like beetles. They are light to dark brown in color, with adults being 3-4 mm long. They are slender with short wing covers. Rove beetles have an interesting habit of curving their abdomen upwards like scorpions and can run or fly when disturbed (usually close to the ground). Since they can actively fly, they rapidly colonize the release area. However, too many Atheta in flight may be because of disturbance to their home.
Application rate: 0.1 to 0.5 per sqft
Stratiolaelaps scimitus
Stratiolaelaps scimitus ‘Womersley’ (formerly Hypoaspis miles) is a native species of soil dwelling mite, which feeds on small insects and mites (e.g., springtails, root mealybug crawlers, spider mites). They move rapidly over the soil surface. Stratiolaelaps are used primarily to control young larvae of fungus gnats in the soil or planting media. To control high numbers of fungus gnats, use of Stratiolaelaps can be integrated with insect parasitic nematodes (e.g., Steinernema spp.) or Bacillus thurinigiensis israelensis (BTI), both of which control the larval stage of fungus gnats. They also help control soil stages of thrips and may account for up to 30% of thrips control.
Application rate: Roughly 25,000 per 1000 square feet of soil medium
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