BIOLOGICAL CONTROL AGENTS FOR SPIDER MITES

Phytoseiulus persimilis

Phytoseiulus persimilis is a specialized predator of spider mites (mainly those in the genus Tetranychus) and is the most commonly used biological control agent for two-spotted spider mite (Tetranychus urticae). 

The adults of P. persimilisare approximately 0.5 mm long (similar in size to adult spider mites), with a pear-shaped body and relatively long legs; adults are a bright orange-red, while the immature stages are a slightly paler salmon color. 

Adult females lay small oval eggs close to or in the webbing of spider mite colonies; the six-legged larval stage that hatches from the egg does not feed, but all subsequent stages (protonymph, deutonymph and adult) will prey on spider mite eggs, immatures and/or adults. Adult P. persimilis can consume approximately 5–7 adult spider mites or 15-20 eggs per day. 

The activity and reproductive success of Phytoseiulus persimilis is strongly influenced by temperature and humidity, with the optimum temperature range being from 20 to 26 °C (68–79 °F), with relative humidities of 65%–80%. At 26 °C, the life-cycle (egg to adult) can be completed in approximately 3 days, and the adults can be expected to live for 12–25 days (depending on host plant) provided that sufficient prey are available. Each female may lay a total of approximately 50–60 eggs. 

Note that while P. persimilis is an excellent predator of spider mites, it cannot survive long in their absence, and does not thrive at temperatures above 30 °C (86 °F). Survival of the egg stage in particular is also greatly reduced by prolonged periods of low relative humidity (55% or less). Reduced efficacy may also be noted on crops with very waxy leaves (e.g. carnations), or those with high densities of glandular leaf hairs (trichomes) (such as most tomato varieties).

Phytoseiulus persimilis is available in pack sizes ranging from 2,000 to 100,000 adults.

Neoseiulus californicus (formerly known as Amblyseius californicus)

Neoseiulus californicus is a predatory mite that develops best on spider mites (a preferred prey), but which can also sustain itself on various other plant-feeding mites (including broad mite (Polyphagotarsonemus latus) and some rust mites), as well as on pollen and small insects (including the immature stages of some thrips). This ability to feed on alternate prey allows N. californicus to persist for longer than the more specialized Phytoseiulus persimilis when spider mites are scarce. 

Adults of N. californicus are an elongated oval in shape and are approximately 1 mm long. The body is a translucent pale pink to pale orange, with the color varying somewhat according to the prey consumed. As with other mites, the egg hatches to a 6-legged larval stage, followed by two successive 8-legged nymphal stages before the final molt to the adult stage.

Neoseiulus californicus develops best at temperatures above 20 °C, with the optimal range being 25–30 °C, with relative humidities of approx.65–76%. However, it is more tolerant of high temperatures and lower humidities than is P. persimilis, tolerating temperatures somewhat higher than 30 °C and relative humidities of approximately 45–50%. At 25 °C, the life-cycle (egg to adult) takes approximately 5 days. At this temperature, adult females will live for approximately 30 days and lay 30–40 eggs. Both development time and adult lifespan will be lower at higher temperatures.

Under conditions that are optimal for P. persimilis, populations of P. persimilis will usually increase faster than those of N. californicus; however, the latter has the benefit of being able to tolerate a wider range of temperatures and humidities, and the ability to persist for longer (on alternative prey) when spider mites are scarce.

Neoseiulus californicus is available in sachets or shaker bottles in pack sizes ranging from 5,000 to 50,000.

Amblyseius andersoni

Amblyseius andersoni is a pear-shaped, pale beige predatory mite less than 1 mm long in the adult stage. This species will feed on a wider range of prey species and alternative food sources than does Phytoseiulus persimilis, including pollen, honeydew, several spider mite species, various other mites (including some russet mites), small insects, and the spores of some fungi. It can also survive for short periods without food.

Amblyseius andersoni can tolerate a relatively wide range of temperatures, although it does best at temperatures above 20 °C (68 °F) and relative humidities of 65% or higher. This species can remain active at 30–35 °C (86–95 °F), although adult life span and egg production are reduced at the upper end of this range. At 25°C (77°F), the life-cycle (egg to adult) can be completed in approximately 6 days, and at this temperature females may live approximately 28 days and lay a total of about 40 eggs.

The relatively long lifespan of A. andersoni, together with its tolerance of relatively high temperatures and ability to utilize a wide range of alternative food sources make it a good complement to P. pesimilis for spider mite management.

Amblyseius andersoni is available in sachets or shaker bottles in pack sizes ranging from 25,000 to 62,500.

Amblyseius swirskii 

This species is a generalist predator often used for whitefly control. However, it will also feed on various species (and stages) of thrips and mites. Like  N. cucumeris (above), it can also sustain itself on pollen when prey is scarce. More details are shown here.

Feltiella acarisuga

Adults of the predatory midge Feltiella acarisuga are delicate, long-legged flies approximately 2 mm in length. Mated females search for spider mite colonies in which to lay their eggs, and on hatching, the orange/red larvae (which are legless and lack an obvious head capsule) attack the surrounding spider mites and suck them dry. They will attack both two-spotted spider mite (Tetranychus urticae) and various other species, including the carmine spider mite, (Tetranychus cinnabarinus). All larval stages are predatory, but the adults feed only on nectar or similar fluids (e.g. aphid honeydew). Pupation occurs inside a silken cocoon on the leaf, usually on the undersurface and close to a main vein.

Depending on temperature and/or relative humidity, developmental time varies from 2 to 4 weeks. Optimum temperature and relative humidity are about 20 °C (68 °F) and 85–90%, respectively. However, reproduction and development will occur at temperatures of between 15 to 25 °C (59 to 77 °F), provided that relative humidity is at least 50%. While this species is more tolerant of low humidity than is P. persimilis, the immature stages do not survive well at temperatures much above 30 °C (86 °F), or relative humidities below 30%.

Feltiella acarisuga is available in units of 250 pupae.