Thrips are a perennial problem in greenhouses everywhere, but biological control is an increasingly popular tool for greenhouse growers to manage these pests.
Here are some of the most commonly used beneficials for thrips, as well as handling, application and management suggestions to help you maximize the effectiveness of each.
Thrips Beneficials (Especially Western Flower Thrips)
■ Neoseiulus cucumeris, Amblyseius swirskii
Pests Attacked: Wide variety of tiny arthropods and especially the smallest lifestage of thrips. A. swirskii also eats whitefly eggs.
Identification: Tiny, pear-shaped, straw-colored mites may run fairly quickly on leaves. Eggs are clear to whitish and oblong like a chicken egg.
Biology: Eggs, several immature stages and adults. A. swirskii is better at warmer temperatures while N. cucumeris is better at cooler temperatures.
How to check for shipment viability: These mites are mixed into a carrier such as bran or vermiculite and shipped in bottles or in little paper sachets. Gently shake the bottle to mix the mites up into the carrier, or open a few of the sachets and sprinkle a small amount onto a white piece of paper. Look carefully, or with a hand lens, for the tiny mites to be running around on the white paper. The straw-colored mites should be running fairly rapidly. Mites will probably also be visible inside the lid of the bottle.
How to release into crop: Mites in bottles are generally meant for broadcasting over the crop canopy. This can be done by hand, or with a modified leaf blower or other dispersal device. Regularly repeated releases are necessary. Mites in sachets are provided food for the predatory mites and meant to release the predators over several weeks (“slow-release” bags). The bags can be spaced among the plant canopy and replaced every several weeks. See detailed directions with the shipment or advice from your supplier.
■ “Hypoaspis” (=Stratiolaelaps scimitus)
Pests Attacked: A wide variety of tiny soil-dwelling insects and mites. It will attack thrips pupae in the soil, as well as eggs and larvae of fungus gnats.
Identification: This mite is generally similar to N. cucumeris or A. swirskii but slightly larger.
Biology: Generally similar to N. cucumeris or A. swirskii; however, they live in the soil and take longer to develop.
How to check for shipment viability: Use the same method as for N. cucumeris or A. swirskii.
How to release into crop: Mites arrive in bottles and can be sprinkled out on the soil surface beneath benches or onto the soil surface of containers at planting. Usually only one or two releases are needed for the mites to become established.
■ Orius insidiosus (Minute Pirate Bug)
Pests Attacked: It attacks a wide variety of insects and mites, including each other (cannibalism).
Identification: Adults are small black and white bugs. Nymphs are orangish. O. insidiosus is often found in flowers with pollen.
Biology: Eggs in plant tissue hatch into predaceous nymphs that molt several times before becoming adults. Adults can fly and disperse very well. They are voracious predators that can kill any mobile stage of thrips that they encounter.
How to check for shipment viability: Orius is shipped as adults mixed with buckwheat hulls in bottles. Opening the bottle should reveal many bugs crawling among the hulls.
How to release into crop: Made for broadcasting into crop canopy, especially in thrips hot spots. O. insidiosus can be difficult to get established in the crop and repeated releases are expensive. Research is underway to find plants (perhaps certain ornamental peppers, alyssum or others) that can serve as banker plants for Orius. It may naturally invade a crop from outside during warm conditions.
■ Nematodes (usually Steinernema feltiae)
Pests Attacked: Many soil-dwelling insects, such as pupating thrips or fungus gnat larvae.
Identification: These are microscopic nematode worms.
Biology: Nematodes need to swim in a water film to search for hosts to infect. They are sensitive to UV light. Nematodes enter an insect host through body openings and release a bacterium that kills the host insect. They may replicate within a host, but usually not in great enough numbers for significant pest control.
How to check for shipment viability: Place a tiny sample of nematodes on a small plate or petri dish. Put a drop of water on the sample. Wait about 10 minutes, and then observe the water drop with lens or microscope. Nematodes that are curled and wriggling are healthy; dead nematodes are stretched out straight.
How to release into crop: Foliar applications may kill a few thrips pupae in the canopy, but the spray runoff into the soil, which kills pupae in the soil, probably has the greatest effect on thrips control. Repeated applications are needed. Nematodes will drown if left too long in water. An excellent video of the use of nematodes from UMass Extension can be found here.