Stethorus – The Ulimate Spider Mite Predator

IMG_1531Quietly gaining recognition for spider mite control amongst the giants (figuratively-speaking) of the industry like phytoseiulus persimilis, amblyseius andersoni, fallacis and californicus, stethorus punctillum is making itself known to growers thanks to its’ flight, hunger, and suitability for hot crops, low humidity and sticky plants.

The “giants” previously listed are all predatory mites. Stethorus is a black beetle. It is sold as hungry adults that quickly fly into your crop to lay eggs where high density of spider mite eggs are present. The adults then leave to go feed on spider mites, mate and lay more eggs. The larva that emerge are fast – like mites – but are restricted to the plants. They will eat a remarkable amount of spider mites before pupating and emerging as adults.

Stethorus need a spider mite population to cycle, but can be used preventatively as long as regular applications are applied.

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Take a look at the pros and cons to see how Stethorus measures-up.

Stethorus Pros:

1. Easy application (fly to find food)

2. Preventative (will fly and search for hot spots)

3. Recovery (can eliminate spider mite populations quickly)

4. Are suitable for sticky plants (like cannabis buds)

5. Are suitable for low humidity (like atriums and cannabis)

6. Handle high heat and low temps (native to North America but have been used in central american banana crops.

7. Can cycle (high spider mite numbers allow them to cycle, but they can overwinter and return to your crops in the spring as well.)

8. Adults and larva are spider mite predators

9. Compatible with all predatory mites for spider mite control.

10. Is comfortable with spider mite webbing.

11. Few stethorus beetles can do the work of thousands of predatory mites.

12. Completely eliminates spider mite populations

13. Do not cannibalize in transit.

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Stethorus Cons:

1. Hard to purposely establish on a specific plant (use persimilis)

2. Will leave when spider mite are gone.

3. Initial price is high (cost is low however, since you need so few).

4. Need adequate light to lay high levels of eggs

5. Hard to find after release (the spread themselves out.)

Reasons not to use persimilis:

1. If many plants are infected and application time and method is an issue

2. Plants are sticky

3. Plants need high heat or low humidity

4. When shipped (unless on leaves) the females eat the males

Reasons not to use Californicus

1. Is not compatible with other mites, as it eats other mites before spider mites.

2. When shipped (unless on leaves) the females eat the males

Reasons not to use Fallacis and Andersoni

1. They will not be as effective against a spider mite infestation.

2. Andersoni needs other food sources present to be effective.

3. When shipped (unless on leaves) the females eat the males

When to use the others:

1. Use fresh persimilis on bean leaves when you want to concentrate efforts on one plant, or if you have the means to apply persimilis to all your plants regularly. Persimilis is inexpensive.

2. Use fresh fallacis on bean-leaves before spider mites appear. They can survive on your plants permanently and eliminate the spider mite threat. The preventative rate is so low that the cost becomes extremely low. Fallacis is highly efficacious.

3. Use Andersoni when you can get it same day or over night. Reapply regularly.

4. Use californicus when it is the only beneficial insect you will be using. Reapply regularly.

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You can see why Stethorus is growing in popularity. As growers learn of its existence and efficacy they are more inclined to drop the predatory mite program (other than also using fallacis as a first step prevention and persimilis to help a hot spot.) The first growers to be entirely on-board with stethorus were the out-door strawberry growers. They found enormous saving in labour for distribution and because stethorus flourished in the low humidity. Likewise, large atriums like those in Las Vegas quickly utilized stethorus as it was the only beneficial insect to control mites on the upper leaves of palms where humidity was unrealistically low. Cannabis growers make up the fast-growing demand. Stethorus reduces their scouting time (as the beetles fly to new areas), they don’t get stuck to sticky buds (like mites do), and they are comfortable in the high heat and low humidity.

Many ornamental growers still use a combination of approaches – that is because spider mite damage is fast and permanent. So fallacis is applied at propagation (and sometimes one or two more times), a small amount of stethorus is applied semi-regularly (basically to police the tops of plants and to become established) and persimilis is used wherever and whenever a growers finds any spider mite at all. It sounds expensive and time consuming – but so does applying a chemical that doesn’t work and then deciding to throw your entire crop out.

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The key to providing inexpensive spider mite control is to be preventative. Remember, clean-up requires stratiolaelaps on the floor/ground to eliminate overwintering spider mites. Fallacis must be applied at propagation, clone arrival/reception of stock, or as first true leaves appear. That, alone, is likely to be all you need if growing conditions naturally favour healthy plant growth. If you’re “pushing-it,” scout regularly and apply stethorus. You’ll be proud and happy.

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