Timing the release of beneficials is critical to biocontrol success

Heidi Wollaeger<wollaege@msu.edu>, Michigan State University Extension, and Dave Smitley, Michigan State University Extension, Department of Entomology - March 02, 2014

Scout incoming propagules for thrips and release beneficials regularly.

Photo 1. Lifecycles of the western flower thrips. Source: University of Florida Extension

Whether it be putting that frozen pizza in the oven or popping the question to your significant other, life is often all about timing. Likewise, implementing a biological control program in the greenhouse is no different. Michigan State University Extension reminds greenhouse growers that releasing beneficials in the greenhouse needs to be done preventatively when plants are first moved into production space to ensure that predators will be able to keep pest populations under control.

In order to provide effective control of thrips with a biological control program, growers must employ an intensive scouting program. In particular, inspect incoming cuttings, plugs and liners before bringing them into the greenhouse with other plant material as it will alert you of a potential problem. Whether growers find thrips on incoming material or not, plan a regular release schedule. For example, introduce A. cucumeris and H. miles predatory mites to control thrips two and four weeks after starting a crop in a production area. If thrips are discovered early or if more than three are found per sticky card per week early in the crop, add a Steinernema feltiae nematode drench or release S. swirski (mite), Atheta coriaria (beetle) or a combination of two of these management methods.

Early releases of A. cucumeris are critical because they are only large enough to eat the first instar larvae. Therefore, it is difficult to control an outbreak of thrips using this species of predatory mite. Table 1 shows the common biological control agents for western flower thrips (Frankliniella occidentalis) and the lifecycle stage (Photo 1) for which they are effective.

Table 1. Life stages of western flower thrips affected by biological control agents.

Biological control agents	Species type	Life stages of western flower thrips affected by biological Control
Biological control agents	Species type	Egg	First instar nymph	Second instar nymph	Pre-pupae	Pupae	Adult
Amblyseius cucumeris	Predatory mite
Amblyseius degenerans	Predatory mite
Amblyseius swirskii	Predatory mite
Hypoaspis miles	Predatory mite
Orius insidiosus	Predatory minute pirate bug
Steinernema feltiae	Entomopa-thogenic nematode				*soil	*soil
Beauveria bassiana	Beneficial fungi

Also when implementing a biological control program, know the insecticides that have been sprayed on the plants. Pesticide residues not only kill your beneficials, but also cause many sublethal effects including altering the sex ratio of males:females, sterilizing females or influencing their foraging behaviors.

So don’t let that pizza burn – scout your incoming propagules and release your beneficial insects before you have an infestation of thrips in your greenhouse!

Dr. Smitley's work is funded in part by MSU's AgBioResearch.

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