Thrips ControlThrips populations should not be a problem until there are large populations of thrips outside the greenhouse. Within a couple weeks thrips populations can explode from developing local populations and those immigrating on wind currents from the south. In our area this is usually toward the end of May but varies with the weather. The predatory mite, Amblyseius cucumeris, patrols tomato leaves and stems searching for thrips larvae. Good biocontrol often involves attacking multiple life stages: eggs, larvae, pupae, and adults. Because thrips pupate in the soil or potting media they are vulnerable to a variety of predators such as nematodes, predatory mites, and rove beetles. Another species of predatory mite, Hypoapsis miles, lives in the upper portions of the soil and will attack pupae of both thrips and fungus gnats. Nematodes released for fungus gnat control will also attack thrips pupae, but do not reproduce well within either host and regular introductions must be made. Rove beetles, Altheta coriaria, is a new predator that shows good promise for both thrips and fungus gnats. They will reproduce if food is available, in about 3-4 weeks. Our tests have indicated an effect on thrips and fungus gnat populations for at least six weeks. This predator can be establish early but should be re-introduced soon after the spring invasion of winged adult thrips. Remember, it takes perhaps two weeks for thrips pupae to show up in the soil after the adults begin to lay eggs.  | These sachet bags are hung from tomato leaves. Tiny predacious mites (Amblyseius cucumeris) reproduce within the sachet bag. They eat grain mites which feed on a supply of ground grain. As predacious mite populations increase they leave the bags though small holes. It takes several weeks after hanging these bags on tomato plants to achieve maximum effect, but there is a continuous supply of predatory mites coming from the bags for several more weeks. | | Rove Beetle Picture | Adult Rove Beetle. Note that the wing covers do not extend over the abdomen. Still, they fly well and will easily disperse within the greenhouse. They search for food within the upper parts of the soil or potting media. |
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