Effective biocontrol programs for western flower thrips often use multiple natural enemies. These include predatory mites like N. cucumeris or A. swirskii, but also generalist predators like Atheta and Orius, which can feed on mite eggs and nymphs.
So, how can you make sure your generalist predators aren’t just eating all your predatory mites, instead of your thrips?
A recent study by Michigan State University suggests that the release strategy you choose for your biocontrol agents can affect whether your bios play nice together or not.
Specifically, they looked at how either breeder piles of N. cucumeris (i.e. small piles of predatory mites, bran and feeder-mites placed on the soil surface) or slow-release mite sachets (paper sachets filled with predatory mites, bran and feeder-mites, hung in the crop), fared in a crop also using Atheta coriaria for biocontrol.
Not surprisingly, the researchers found that a high number of Atheta invaded the breeder piles on the soil surface, but that Atheta rarely ever found their way inside sachets (Fig 1). Unfortunately, the end result was that breeder piles produced 6-8 fold fewer predatory mites than sachets did, likely due in part to Atheta consuming eggs and nymphs of N. cucumeris.
The team at MSU also did a separate test to look at dispersal of mites between the two release strategies – because what good is a lot of predatory mites if they just want to stay home and watch TV instead of going out to eat? The researchers found that more mites dispersed from sachets compared to breeder piles, and that they continued to disperse for a longer period (Fig. 2, below).
Overall, this study showed that the use of mite sachets helps defend predatory mites against intraguild-predation (i.e. being eaten by another beneficial!), AND that sachets result in more predatory mites dispersing onto plants than breeder piles. This sounds like a win-win to me!
So if you’re currently using breeder piles, you may want to take a second look at sachets to achieve the best thrips control possible in your greenhouse.