How are YOU controlling your Echinothrips? (Photo by Entocare NL).
Echinothrips americanus is an interesting pest in Ontario. An occasional pest of little concern for some, its presence often plagues others (i.e. cut flower growers). The greenhouse research team at Wageningen University & Research has been working to find reliable, effective biocontrol strategies for this Echinothrips.
Read on for their latest update on what’s working, and how this applies to Canadian growers.
Note: This is a re-post but contains important information on use of DDVP (dichlorvos) with mite sachets. (See point 4!)
In 2017, I had an interaction with a grower where their long-standing biocontrol program for thrips suddenly seemed to be failing. After a (too long) investigation by myself, the grower, and consultants, we found out the horrible truth: their predatory mites were being MURDERED (Duh dun DUHNNN!)… By improper storage.
This post focuses on all the ways YOU might also be guilty of mite murder, and how to make sure your mites are still alive and kicking in those little sachets.
(And yes, I’ve stooped to the level of click-bait titles).
NOTE: This is a re-post because it now comes with an awesome new video of how to monitor you mite sachets!
Recently, I had an interaction with a grower where their long-standing biocontrol program for thrips suddenly seemed to be failing. After a (too long) investigation by myself, the grower, and several consultants, we found out the horrible truth: their predatory mite were being MURDERED (Duh dun DUHNNN!)… By improper storage.
This post focuses on whether YOU might also be guilty of mite murder. (And yes, I’ve stooped to the level of click-bait titles).
As much as we all hate thrips, there are, frankly, worse problems to have. And it’s name is Leafminer. These flies cause just about the ugliest damage we see in floriculture (Fig. 1), and they have incredible pesticide-resistance capabilities. Outbreaks seem to go in cycles, and I’ve had quite a few gerbera and mum crops come across my desk with leafminer this past 2 weeks.
This post covers chemical options (BawHawHawHa!!! Oh… Sorry… I’ll get myself under control now) and non-chemical options for leafminer, as well as how their control fits into the big picturein greenhouse IPM programs.
Western flower thrips adult on an open Mandevilla flower. Photo credit: Caitlin MacDonald, USEL student.
Now that the warm weather is finally upon us, it’s time to start worrying about thrips control.
What we’ve learned over the years is that pesticides just don’t cut it – the only reliable chemical for western flower thrips in Ontario is DDVP, which requires constant application. This means biological control is your best bet. Here’s a summary of the most effective tools, tricks, and timing, to ensure your biocontrol dollars are well spent.
Entomopathogenic nematodes – used to control fungus gnats, shoreflies and thrips – are often a “gateway bio” into biocontrol use in greenhouses. This is because not only are they effective and easy to use, but they’re generally compatible with insecticide use. Readily applied with regular spray equipment or through drip lines, nematodes can even be tanked mixed with pesticides to save on labour costs.
In this post, I’ll share some of my research at NC State, looking at which commonly used pesticides in Canadian and U.S. greenhouses are safe to use with nematodes.
Effective biocontrol programs for western flower thrips often usemultiple natural enemies. These includepredatory mites like N. cucumeris or A. swirskii, but also generalist predators like Atheta and Orius, which can feed on mite eggs and nymphs.
The spring bedding crop season is over, so now’s the time to reflect on what worked, and what didn’t, for foxglove aphid control. This way we can prepare for their re-appearance in the fall.
Foxglove aphid feeding on pansy. Note the characteristic dark-green blotches on the abdomen, and the dark joints of both the legs and antennae. Photo by S. Jandricic, OMAFRA.
To recap, foxglove aphid (Aulacorthum solani) is a “cool weather pest”. It prefers temperatures between 15-25 C, and can’t survive in the greenhouse in summer (1). Unlike other aphid pests, foxglove aphid tends to feed in hidden locations – primarily the lowest leaves of plants – making it difficult to detect and treat.
And, unlike green peach and melon aphid, biological control of foxglove aphid is definitely a challenge.
Some growers and consultants have been trying both Aphidius ervi and Aphidius matricariae for foxglove aphid. But, as demonstrated by the Buitenhuis Lab here at Vineland, foxglove aphid is a terrible host for A. matricariae, and this wasp will barely parasitize it (see graph). Further, using A. matricariae for foxglove aphid can actually end up spreading this pest, and it’s damage (2). This is because the wasps simply pesters the aphids to the point where they drop of the plant and go find a quieter place to eat. So it’s pretty clear that releasing A. matricariae is simply a waste of money and effort if you’ve got foxglove aphid.
Parasitism rates of foxglove aphid by different Aphidius species. Wasps were offered 50-60 2nd instar aphids. Tests were done in small plastic containers.
But what about A. ervi? Although parasitism rates were high in the lab (73%), results were not as good in practice. Tested in the greenhouse, A. ervi was able to offer about 50% control of foxglove aphid after 1 release.Repeated releases may offer greater control, but this is still not reassuring when you’re talking about a pest where populations can explode quickly.
Why A. ervi does a great job of parasitizing foxglove aphid the lab, but not the greenhouse, is something we’re currently investigating. But until we have an answer, it seems that pesticides may currently be the best option for control of foxglove aphid in floriculture IPM programs. With the current limitations on neonicotinoids, growers will want to turn to Beleaf or Endeavor. (But, since these two chemicals have similar modes of action, and it usually takes several sprays of either to provide complete control, you may want to consider rotating these chemicals with Enstar II to prevent resistance).
If you’ve had infestations of foxglove aphid in your greenhouse, and have anything to say about it’s control, feel free to leave me a comment!
(1) S.E. Jandricic, S.P. Wraight, K.C. Bennett, and J.P. Sanderson. 2010. Developmental times and life table statistics for the aphid Aulacorthum solani (Hemiptera: Aphididae) at six constant temperatures, with recommendations on the application of temperature-dependent development models. Environmental Entomology 39(5): 1631-1642.
(2) L. M. Henry, J.A. Bannerman, D.R. Gillespie2, and B.D. Roitberg. 2010. Predator identity and the nature and strength of food web interactions. Journal of Animal Ecology doi: 10.1111/j.1365-2656.2010.01723.x.
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. cucumerisandA. swirskii.
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.