Predatory Mites & Targeted Pests in Organic Cannabis Pest Control

adult predatory mite killing two-spotted spider mite
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Mites don’t have the best reputation when it comes to the general public but cannabis growers pay thousands of dollars every year to get them into their grow rooms. This is because mites can either be marijuana bugs or predators in the greenhouse. In fact, most of the cannabis crops grown in Oregon are produced with the help of predatory mites and bugs.

There are many types of predatory mites, each with their selected food sources. Life cycles are similar to many cannabis pests, starting with the egg stage, the larval period, the nymph stages and finally the adult. Except for the egg stage, all other life stages are predatory.

Predatory mites might be small but they are extremely voracious. They eat a variety of plant-consuming mites, bugs and other insects. Where prey is absent, most predatory mites sustain their populations by eating pollen or nectar, which additionally makes them valuable as a preventative measure on your crops.

Predatory mites are among beneficial insects commercially produced for the cannabis industry. They have attracted a lot of attention due to their role in the biological control of small arthropods. Pesticide resistance in many marijuana pests have further boosted their importance in cannabis pest management, and growers are turning to predatory mites as permanent solutions.

Specialist vs Generalist Predatory Mites

Predatory mites can be categorized as specialist or generalist predators. Specialist predators are used for targeting specific pests while generalists are used as a preventative method against a variety of different pests. Different species of predatory mites prefer different environments in order to work optimally. Some thrive best on smooth leaf surfaces while others like hairier plant varieties better. Obviously, one mite will not fit in all situations, and having a good understanding of different types of mites and their behaviours is important to establishing a successful IPM program.

Specialist predatory mites work best as a curative method at the beginning of a cannabis pest infestation. They should not be used as a preventative measure because specialist predatory mites need specific prey to feed on or else they will starve and die. Specialist predatory mites generally reproduce faster, have better search abilities and can lower the pest prey population more quickly. An example of specialist predatory mites is Phytoseiulus persimilis. It has the capacity to rapidly respond numerically to increasing two-spotted spider mite populations, which makes this predatory mite the appropriate choice for augmentative biological control programs.

Generalist predatory mites, on the other hand, are more effective when pest populations are low and more dispersed. When applied as an augmentative measure, these predatory mites commonly stay and breed in good numbers because they utilize a variety of food sources, feeding on pollen, fungal spores, and plant exudates. However, generalist predatory mite females disperse more slowly and deposit eggs over an extended period of time. An example of generalist predatory mites is Amblyseius swirskii which has proven to be very effective against marijuana pests such as broad mites and cyclamen mites, as well as whiteflies and immature thrips.

In most cases, several releases may be needed when using specialist predatory mites whereas only one release of generalist predatory mites may be required. Furthermore, generalist predatory mites are more effective when pest populations are dispersed while specialist predatory mites work best with concentrated infestations.

Now let’s take a look at the more common predatory mites used in organic and integrated cannabis pest control programs.

Phytoseiulus persimilis

Phytoseiulus persimilis predatory mite for two-spotted spider mites

Phytoseiulus persimilis is a specialist predatory mite used to suppress two-spotted spider mites and bean red spider mites in fruit, ornamental and market garden crops. It is one of the oldest biological control agents, first used commercially in 1930. Adults are pear-shaped, orange in color, 0.5 mm long, with long legs. Their oval-shaped eggs measure about 0.33 mm in diameter, twice the size of that of two-spotted spider mites. Persimilis is also more mobile and depends almost entirely on spider mites for food. Once their prey is depleted, predatory mite populations will decline in numbers. 

A broad range of both indoor and outdoor crops can benefit from Persimilis. Best results are achieved when used with the predatory beetle Stethorus punctillum and the predatory mite Neoseiulus fallacis.

The Phytoseiulus persimilis life cycle is 5 days at 77 °F or 25 days at 59 °F. Optimal conditions are temperatures between 68 °F and 81 °F, with over 60% relative humidity. A female lays 2-3 eggs per day, for a total of 60 eggs. Adults live more than 35 days. Persimilis consumes 5 to 30 prey (eggs or mites) per day and does not enter into diapause.

Targeted Pests

  • Two-spotted spider mites
  • Bean red spider mites

Neoseiulus californicus

Neoseiulus californicus predatory mite for spider mite and broad mite control

Neoseiulus californicus predatory mites are widely used for spider mite and broad mite control in fruits, vegetables, ornamentals, and cannabis crops. It consumes egg, nymph and adult stages of pest mites and is also considered a generalist that can attack thrips and other invertebrates. The adult is translucent orange-beige, pear-shaped with long legs and measures 0.5 mm. The eggs are round, transparent and measure 0.05 mm in diameter. Nymphs (juvenile stage) look like adults except that they are smaller. N. californicus develops faster when consuming the two-spotted spider mite. It can also eat pollen, thrips and other small insects, but its reproduction will be slowed down with this diet. It is among the most voracious predatory mites and can attack other biological control agents such as  Phytoseiulus persimilis or Neoseiulus cucumeris nymphs and eggs.

N. californicus thrive in temperatures between 61 and 89 °F and relative humidity between 40 and 80%. On average, they eat 5 prey each day but become inactive under 10°C. Their life cycle lasts approximately 7.5 days at 77 °F and they do not enter diapause. A female N. californicus lays about 4 eggs a day or up to 43 eggs in its lifetime.

Targeted Pests

  • Spider mites
  • Broad mites
  • Cyclamen mites
  • Russet mites
  • Thrips
  • Other invertebrates

Neoseiulus fallacis

Neoseiulus fallacis predatory mite for two-spotted spider mites cyclamen mites broad mites

Neoseiulus fallacis are native North America predatory mites used to suppress cannabis pest mites such as two-spotted spider mites, spruce spider mites, European red mites, cyclamen mites and broad mites. Adults are 0.5 mm long, pear-shaped, with long legs. They can vary in colour from cream to orange-beige. Their oval-shaped eggs measure 0.33 mm in diameter (twice the size of a two-spotted spider mite egg).

Neoseiulus fallacis can tolerate both heat and cold and has excellent dispersal abilities. It is most active in temperatures ranging between 48 °F and 89 °F. When pest populations drop to lower levels, these tenacious predatory mites survive better than the others. Fallacis can be used in combination with the predatory beetle Stethorus punctillum and the predatory mite Phytoseiulus persimilis to successfully eradicate spider mites.

Neoseiulus fallacis has a life cycle of 7 to 9 days at 70 °F or 3 days at 89 °F. Adults live from 14 to 62 days. N. Fallacis is active from 48 °F to 89 °F and needs humidity levels over 50%. Females lay 1-5 eggs per day, for a total of 26 to 60 eggs in their lifetime. A female gobbles up anywhere from 2 to 16 spider mites each day. Outside, adult females enter diapause when the days get shorter (less than 14 hours of light). Neoseiulus fallacis will not enter into diapause in greenhouses when temperatures are kept over 64.5 °F.

Targeted pests

  • Two-spotted spider mites
  • Spruce spider mites
  • McDaniel spider mites
  • Broad mites
  • Tomato russet mites

Neoseiulus cucumeris

Neoseiulus cucumeris predatory mite for thrips, two-spotted spider mites, cyclamen mites, broad mites

Neoseiulus cucumeris are predatory mites used to suppress immature thrips, two-spotted spider mites, cyclamen mites, broad mites and mites of the genus Schizotetranychus. The adult is pear shaped and about 0.5-1.0 mm in length. Before cucumeris mature to adults, they grow through one larval stage and two nymphal stages. The life cycle from egg to adult is completed in 10 to 12 days at 72 – 80°F. The adults will live for about 25-35 days and will eat an average of 1 thrip per day.  An adult female produces 1-3 eggs a day and an average of 35 eggs during her lifetime. Eggs are oval, translucent and laid on leaf hairs on the lower surface of the leaf. They hatch in about 3 days but the larvae won’t feed until they molt for the first time 2 days later. The nymphs also have big appetites for pests during the two nymphal stages which can last for 7 to 10 days before they start changing into adults.

The cucumeris can survive on a pollen-only diet but it seems to thrive when they have live prey to eat. They are lazy predatory mites but they won’t travel very far to hunt.  So if you have pests high in your canopy and in the soil, release some on both levels.

Targeted pests

  • Onion thrips
  • Western flower thrips
  • Eastern flower thrips
  • Cyclamen or strawberry mites
  • Broad mites
  • Spruce spider mites
  • Mites of the genus Schizotetranychus

Amblyseius andersoni

Amblyseius andersoni predatory mite for pre-emergent control of mite infestations

Amblyseius andersoni are predatory mites native to North America and is an excellent choice for pre-emergent control of mite infestations. Highly versatile and resistant to fluctuating temperatures, they feed on and control all stages of phytophagous mites, with all mobile life stages of A. andersoni acting as predators. 

A. andersoni larvae emerge from a single egg 2-3 days after female adult laying. They undergo 2 nymphal stages (protonymph and deutonymph) prior to adulthood. Development from an egg to an adult takes 8-11 days at 68 – 77°F. Adults live for about 3 weeks. Predators may diapause in response to temperature drops and diminishing light in late summer or fall (<10-hour light periods), however, they can survive winter conditions and reemerge under increased ambient temperatures in the spring. Optimal conditions for A. andersoni are at temperatures ranging from 68 – 100°F, but they can remain active down to 42°F.

Targeted pests

  • Broad mites
  • Spider mites (including two-spotted spider mites)
  • Russet mites
  • Cyclamen mites

Amblyseius swirskii

Amblyseius swirskii generalist predatory mite for immature thrips, two-spotted spider mites, cyclamen mites, and broad mites

Amblyseius swirskii
are very effective generalist predatory mites used to suppress immature thrips, two-spotted spider mites, cyclamen or strawberry mites, and broad mites. Adults are pear-shaped, 0.5 mm long, with long legs. The eggs are round and transparent and measure 0.14 mm in diameter. These mites lay their eggs on trichomes or leaf hairs and along the veins on the inner surface of leaves. The eggs hatch about 3 days later. Like generalist insect predators, A. Swirskii can maintain its population even when there are no more thrips on the plants and start working as soon as thrips reappear. A. swirskii is not susceptible to diapause so it can be used throughout much of the season.

Amblyseius swirskii has a life cycle of 7 days at 77 °F. Optimal conditions are 77 to 83 °F with 70% relative humidity. Females lay 2 eggs per day. They do not enter diapause but become inactive in temperatures below 59 °F.

Targeted pests

  • Broad mites
  • Two-spotted spider mites
  • Tomato Russet mites
  • Whiteflies
  • Onion thrips
  • Western flower thrips
  • Eastern flower thrips
  • Echinothrips

Stratiolaelaps scimitus

Stratiolaelaps scimitus predatory mite for thrips, fungus gnats, root aphids

Soil-dwelling Stratiolaelaps scimitus are predatory mites which feed on thrips (pre-pupa and pupa), fungus gnats, root scales, root aphids, mealybug crawlers, and spider mites in greenhouses and hydroponic crops. This product is perfect for an in-depth “cleaning” of the soil before starting the season. Adults are light brown and less than 1 mm long. They move quickly at the soil’s surface. After mating, the female lays eggs in the growing medium. Juveniles are also predators and feed on the small pest they find in the soil.

Stratiolaelaps scimitus has a life cycle of about 18 days at 68 °F. The sex ratio is equal, 1 female for every male. Eggs hatch in 2 to 3 days. Each Stratiolaelaps scimitus eats 1-5 prey per day. If they lack food, these predatory mites become detritivorous, eating algae and vegetable debris.

Targeted pests

  • Fungus gnats
  • Thrips
  • Diapausing pest mites
  • Bulb mites (Rhizoglyphus spp.)
  • Collembola
  • Vine weevil (Otiorhynchus sulcatus)
  • Nematode pests

Stethorus punctillum

Stethorus punctillum spider mite destroyer predatory mite

Also known as “The Spider Mite Destroyer”, Stethorus punctillum is a small black ladybug with small yellow antennae and measuring nearly 1.5 mm. The eggs are oval and yellow while the larva is dark in color. They are usually deposited near the colonies of pest mites. Larvae and adults are predators and feed on all stages of several mite species such as two-spotted spider mite, spruce spider mite, southern red mite and European spider mite.

The life cycle of the S.punctillum is 14-20 days at 61-79 °F. Optimum conditions are temperatures between 61 to 95 °F and relative humidity between 30 and 90%. The female lays 3-13 eggs a day. Each larva may consume up to 240 mites during its development. The duration of the larval stage is 10 to 14 days. The larva is transformed into a pupa under the leaves or structures. Adults emerge after 6-7 days. The adult can eat 50 eggs and 10 spider mites per day. Below 53 °F, the ladybug becomes inactive.

This little ladybug has demonstrated excellent ability to control pest mite infestations. It flies with a lot of ease and is able to detect outbreaks of infestations. Unlike Neoseiulus fallacis and Phytoseiulus persimilis, it can be used in crops with low humidity and high temperature.

Targeted pests

  • Two-spotted spider mites
  • Spruce spider mites
  • Southern red mites
  • European red mites

Delphastus catalinae

Delphastus catalinae whitefly lady beetle predatory bug

Delphastus catalinae (commonly known as the whitefly lady beetle) is a functional whitefly predator belonging to the family of lady beetles. This small black beetle has been utilized to eradicate and control almost every species of whitefly that afflicts commercial grow operations. Its natural host is Bemisia, a genus of whiteflies native to Florida. For this reason, the whitefly lady beetle will search for and annihilate any Bemisia colonies before moving on to other whitefly species.

Adults are tiny hemispherical beetles measuring 1.4 mm (1/15 inch) long. They are usually dark brown to black. The complete life cycle takes 25-21 days at 77-86°F. Optimal conditions for development are temperatures between 60 and 95°F, with 30 to 80% relative humidity. On a daily basis, Females lay anywhere from 2 to 6 eggs for a total of more than 300 eggs in their 65-day lifetime. Adults devour between 150-640 whitefly eggs or 11 large larvae each day. A single whitefly lady beetle can eat up as many as 700 larvae or 10,000 whitefly eggs in its lifetime. They are not active below 55°F.

Adult whitefly lady beetles are able to detect pest outbreaks and will disperse by flying in the infected area. Delphastus can be used in combination with the parasitoid wasp Encarsia formosa as it does not eat the parasitized whitefly.

Targeted pests

  • Greenhouse whitefly
  • Banded-winged whitefly
  • Silverleaf whitefly
  • Woolly whitefly

Encarsia formosa

Encarsia formosa parasitic wasp

Encarsia formosa is a parasitic wasp that infests whiteflies of the genus Bemisia as well as greenhouse whiteflies such as Trialeurodes vaporariorum. It was the first biological control agent developed to address and control pest populations in greenhouses. Adults are black with a yellow abdomen, measure less than 1 mm long. Encarsia formosa has a life cycle of approximately 28 days at 70°F. At the adult stage, they can live from a few days to a month, depending on the temperature. The optimum conditions are above 68°F and relative humidity of 50-70%. The females lay eggs in 2-week-old whiteflies (third and fourth larval stages) on an average of 10 eggs per day for a total of 200-350 eggs in their lifetime.

Targeted pests

  • Greenhouse whitefly (Trialeurodes vaporariorum)
  • Whitefly Bemisia sp.

Organic pest control is important for predatory mites

The development of cannabis pest infestations can be quite devastating for cannabis grow facilities. Cannabis is grown for human consumption and every effort should be made to grow the crop without the use of potentially harmful pesticides. When it comes to maintaining the ideal cannabis growing environment, an organic IPM (integrated pest management) plan is essential. 

Ant & Garden Organic Pest Control in Beaverton Oregon offers a variety of solutions for organic growers to use in order to minimize damage and prevent pests from taking over a grow space. By incorporating organic systems such as the use of predatory mites and beneficial insects, Ant & Garden Organic Pest Control helps minimize the damage that common cannabis pests can cause by controlling their populations down to manageable levels without you worrying about harming or damaging your cannabis crops!

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