Thrips are a widespread threat in most environments, entering growing spaces a variety of ways on new plant material, your clothing, pets, or flying in from outside. Once in the growing space, thrips immediately begin damaging plants by a combination of feeding and ovipositing (egg laying). They then feed on plants by piercing the cells and sucking out the inner leaf, causing the characteristic silvering damage seen on leaves and disrupting the photosynthesis process affecting yields. Thrips are also one of the primary vectors of plant viruses.
Not having a multifaceted biocontrol approach that targets the different thrips life stages is the most common issue in failed thrips control programs. Thrips eggs are deposited into the leaf tissue, flowers, or in the soft parts of stems, hiding them from natural enemies. From here they will hatch into their larva form and move onto the plants surface to begin feeding. At this stage it is best to use foliage-dwelling predatory mites like Amblyseius swirskii (Swirski), Neoseiulus cucumeris (Thripex), or Amblydromalus limonicus (Limonica). These feed primarily on the first larva stage of thrips species and are great crop defenders. (Read our “Get Rid of Thrips Naturally Using Predatory Mites” article. This will help you choose which predatory mite is best to use in your growing situation) However, it is difficult for any predator mite to control anything larger than the first larval stage, due to size and because larger adults will try to defend themselves by violently jerking their abdomens or in the case of adults, by flying away. If you are only using predatory mites to combat a thrips infestation, this leaves several life stages not targeted such as larger (second plus instar) larval stages, the pupae stage, and adults. In many situations it is necessary to close these gaps with other biocontrol species for proper thrips control.
After the larval stage, dependent on thrips species, thrips will either pupate in the soil or on the leaf. Most common thrips species, like the Western Flower Thrips (Frankliniella occidentalis), Onion Thrips (Thrips tabaci), or the European Flower Thrips (Frankliniella tritici) fall off the leaf, pupating where they land, which is usually in the soil. Adding a soil-dwelling predatory mite such as Stratiolaelaps scimitus (Entomite-M), the predatory bug Daltoia coriaria (Atheta) or the nematode Steinernema feltiae (Entonem) closes this gap. All three of these products inhabit the top layer of the soil targeting thrips pupae. When dealing with Echinothrips (Echinothrips americanus) commonly found on ornamentals and/or tropical houseplants, you can skip treating the soil-dwelling stage, as they only pupate on the leaf.
Once common thrips species have finished pupating, they will develop wings flying back onto the plants as an adult to start the feeding/egg laying portion of the life cycle again. Here you will get the best control with Horiver cards (blue) and the predatory bug Orius insidious (Thripor). Orius will actively search the crop for its prey, being attracted to damaged leaves and actively reacting to any pest movement found on the plants. They will feed on any mobile thrips in the crop (larva and adults).
For larger thrips species more common in tropical plants, it is best to use a combination of Chrysoperla carnea (Chrysopa) to target the larger size larvae and Horiver cards to trap adults. Echinothrips (Echinothrips americanus), Greenhouse Thrips (Heliothrips haemorrhoidalis), or Anthurium Thrips (Chaetanaphothrips orchidii) are all common examples of these larger species that are not controlled by typical predator mite/Orius strategies.
Introducing multiple bio-controls into your crop, depending on thrips species, will provide you with the utmost support needed to combat this pest and its difficult life cycle. Thus, allowing you to close the loops in your thrips program by using a three-pronged approach targeting larvae, pupa and adults.
(Above: Western Flower Thrips Life Cycle - Bio-control may need to be applied multiple times to completely eradicate this pest. Apply bi-weekly or monthly until no thrips are found on your plants for at least a month.)