Snack attack: how to help prevent your thrips bios from eating one another

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? Continue reading “Snack attack: how to help prevent your thrips bios from eating one another” →

New tool in floriculture IPM: testing your microbial products.

What’s the first thing you do with your shipments of predatory mites, parasitoids and predators when you receive them? You probably check to see if these natural enemies are alive before you put them out in the crop.

Now Albert Grimm (Jeffries Greenhouses) and I have come up with a way to check if many of your microbial products are still viable, too.

We’re still in the process of testing these methods for all microbial products, so please consider this preliminary. Right now, we know this works for Beauveria and Metarhizium-based products only (e.g. BotaniGard, BioCeres and Met52). I’m hoping to put the methods up for more products in December.

Supplies Needed:

**Figure 1.** Various fungi growing on a 3M Yeast and Mold Petrifilm

3M™ Petrifilm™ Yeast and Mold Count Plates. These are pre-loaded with media that grow a variety of fungi (Fig. 1). They are about the size of one playing card, are relatively affordable ($113.97/50), and are easily stored (click here for more handling details).
Disposable plastic water cups that hold at least 200 ml
Rubbing Alcohol
Small measuring spoon, like the kind you use in baking (i.e. can measure 1/8^th of a teaspoon)
Disposable plastic pipettes (Fig. 2). I bought 0.2ml ones from Amazon.ca ($4.16 for 100).
- Distilled (sterile) water. Unopened bottled water will do in a pinch. Do NOT use tap water.

Methods:

**Figure 2.** 0.2mL sterile, disposable pipettes that can be obtained from Amazon.ca.

Step 1: Disinfect the water cup and the measuring spoon with rubbing alcohol. Wipe dry with paper towels.
Step 2: In one plastic cup, add a small amount of sterile water (a few mL is fine). Keep for Step 4 to act as a control.
Step 3. Take a second cup to mix up your product in. Add 200 mL of sterile water. Then add approx. 1/16^th of a teaspoon (0.3ml) of product (Beauveria or Metarhizium). To measure, fill the smallest baking measuring spoon (1/8^th of a teaspoon) about half way. Stir well. This will give an approximate concentration of 1 g/L, which is similar to recommended rates of these products.
Step 4: Take a disposable pipette and fill with sterile water. (Make sure to re-seal your bag of pipettes so they stay clean and sterile). Grab a single Petrifilm and peel back the thin, clear cover on top. Carefully squeeze the pipette to form a line of water across the surface of the Petri film.
Step 5. Repeat Step 4 on the same Petrifilm using your product in solution. You can use the same disposable pipette (since it only had sterile water in it previously).

Figure 3. Photo courtesy of Albert Grimm. A 3M Petri Film used to test the viability of Met52 and BotaniGard microbial pesticides. The blank water control indicates that all fungal spores came from the products, not from the water source (here, distilled water). — Figure 3. Photo courtesy of Albert Grimm. A 3M Petrifilm used to test the viability of Met52 and BotaniGard. The blank water control indicates that all fungi came from the products, not from the water source (here, distilled water).

Step 6. Gently drop the plastic cover back over the Petrifilm. Write directly on the plastic cover with a sharpie to indicate the position of your “control” water line and your “product” water line (see Fig 3). Store the film between 20-25 °C in a dark location.
Step 7: After a minimum of 16 h (the time it takes for Beauveria spores to germinate), check your Petrifilm. The sterile water line should be blank. The Beauveria and Metarhizium lines should be light blue -the film has a dye in it that reacts to fungi (Fig. 3). Note that this dye reacts to ANY fungi or yeast. Thus, you CANNOT use it to diagnose what fungus is growing. This is why the sterile water control is so important – you want to be sure the reaction is from your microbial product, and not from random fungal spores in your water.

With the growers still tentative in their use of microbial-based products, this viability test may give growers some piece of mind. It will be particularly useful for product that’s been shipped in hot summer months, or in the dead of winter, as some products are sensitive to extreme temperatures. It can also be used to test product that has been sitting in storage for long periods.

Note that this is a simple live/dead test. These methods do not quantify how much of the product is still viable. That’s something Dr. Anissa Poleatewich (Vineland) and I are working on, as we think it would be useful to know if your product is decreasing in efficacy over time. So, stay tuned for more information as we perfect our methods.

When “harassment” is a good thing in your greenhouse

Well, now that I’ve gotten your attention, let’s be clear that I’m talking about bugs, here, people. Specifically, Western flower thrips and predatory mites such as N. cucumeris and A. swirskii.

L2 western flower thrips next to a predatory mite egg (left) and 2 adult mites (right). — Second instar (L2) western flower thrips next to a predatory mite egg (left) and 2 adult mites (right). Photo credit: Sarah Jandricic.

We all know that predatory mites only kill and eat the small, first larval stage of thrips (referred to as L1’s). Larger life stages (i.e. L2’s and adult thrips) are simply too large for the mites to kill.

But, that doesn’t mean they don’t help control them.

Predatory mites will repeatedly attempt to kill L2 thrips – attacking them up to 40 times an hour ⁽¹⁾. The L2 thrips are able to fend off these attacks by either running away, or “slapping” mites in the face with their abdomens. You can watch the hilarity that ensues when mites attempt to attack too-large thrips larvae here.

But this “harassment” by mites takes it’s toll on thrips. Because thrips spend more time fending off mites, they spend 30% less time feeding ⁽²⁾. Over time, this translates to 40% less damage on plants with predatory mites, compared to no mites ⁽²⁾. And, the presence of mites can reduce survival of L2 thrips by up to 78% ⁽¹⁾, probably because eating less means the thrips lack the nutritional reserves to complete development.

And all of this is accomplished just through “intimidation” of thrips by mites – not through consumption. Scientists term these “non-consumptive” effects, and we are just starting to learn the importance of these effects in biological control. Research is now suggesting that non-consumptive effects like “harassment” may actually account for 50% of the pest control we see in greenhouses ⁽³⁾.

This makes sense with our thrips example. Not only do mites reduce the feeding and survival of larval thrips, but ongoing research from Cornell University shows that the presence of mites reduces the number of eggs laid by adult thrips, and shortens adult thrips lifespan ⁽⁴⁾. Even the presence of predatory mite eggs on a plant has been shown to “scare” L1 thrips into eating less, according to research from Austria ⁽⁵⁾.

And, it would make sense that the more mites you have, the higher the number of “scary” encounters thrips will have with them, improving control.

So, lets give a hand to the hard working, harassing, predatory mite, who’s doing more than we ever thought in floriculture IPM. Stay creepy, little guys. Stay creepy.

References: (1) Jandricic, S.E., Schmidt, D., Bryant, G., and Frank, S.P, NC State University. Unpublished data. (2) Jandricic, S.E. and Frank, S.P. 2014. Too scared to eat: non-consumptive effects of predatory mites. IOBC/wprs Bulletin 102: 111-115; (3) Preisser, E. L, Bolnick, D. I., & Benard, M. F. 2005: Scared to death? The effects of intimidation and consumption in predator-prey interactions. Ecology 86: 501-509. (4) Loughner, R., and Nyrop, J. Cornell University. Unpublished data. (5) Walzer, A., & Schausberger, P. 2009: Non-consumptive effects of predator mites on thrips and its host plant. Oikos 118: 934-940.