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Greenhouse Updates: Feb 4, 2019

Biocontrol Profile: Mighty Mites, Part II
Feb 4, 2019

See Part I of this two part series here

Several predatory mite species are available as biological control agents (BCAs) for common greenhouse pests. Some of the more common species are described below.

Neoseiulus cucumeris: Formerly Amblyseius cucumeris, this generalist predator will eat thrips 1st instar nymphs, whitefly, aphids, and psyllids. They also prey upon other types of mites, but may be more effective for control of eriophyid and broad mites than spider mites. N. cucumeris will go after the most readily available prey, so if pests are abundant on plant leaves they may not go into flowers to hunt for thrips. In situations such as this it is necessary to apply a higher rate of mites. Optimum conditions for N. cucumeris are 68-77° F and 65-70% relative humidity (RH). They fare poorly when the temperature exceeds >90°F. N. cucumeris is susceptible to diapause; however, non-diapausing strains have been discovered and are available from some suppliers. For whitefly and thrips management, best results may be obtained when N. cucumeris is used in combination with Amblyseius swirskii.

Amblyseius swirski: Swirski mites prefer whitefly eggs and larvae, thrips larvae, and 1st and 2nd instar thrips nymphs. They will also prey upon other mites, but this is not their preferred diet. They may be less effective when multiple pest species are present. A. swirski will eat nectar as well as pollen in the absence of insect prey, but keep in mind that the performance of BCAs is best when their preferred prey is available. They thrive at higher temperatures than N. cucumeris (optimum 66-97°F); many growers use a combination of the two species to optimize biocontrol efficacy over a range of temperatures. Swirski mites do not go into diapause, so they can be used most of the year if temperatures are >72°F.

Neoseiulus californicus (Formerly Amblyseius californicus): This mite will feed upon all stages of various pest mite species, but appear to prefer Tetranychidae, the family that includes the two spotted spider mite (TSSM). N. californicus is tolerant of a wide range of temperatures (50-100°F) and RH in the range of 40-80%. They are generally less voracious than N. cucumeris and A. swirskii, but have the potential to persist for longer periods of time in the greenhouse.

Stratiolaelaps scimitus (formerly Hypoaspis miles): These predatory mites are unlike others used for biocontrol in that they prefer to live in the top half inch or so of soil, where they prey upon fungus gnat larvae and thrips pupae. They will also consume algae and plant debris. The principal strength of this species is fungus gnat control, for which it is often used in conjunction with Steinernema nematodes. S. scimitus may also be applied along with N. cucumeris for thrips management. Optimum conditions are 60-74°F at the soil surface and high humidity. They are inactive below 57°F but are not subject to diapause.

Phytoseiulus persimilis: P. persimilis is especially good for spider mite control in greenhouses during the warmer months, preying upon all life stages of the pest. Optimum conditions for this mite are 68-90°F and 60-90% RH. Although P. persimilis is voracious and sometimes recommended for inundative biocontrol, the reproductive rate of the two spotted spider mite will exceed that of P. persimilis at temperatures above 86°F. This species is not subject to diapause. In contrast to most other predatory mites used for biocontrol, P. persimilis will not eat pollen or prey other than spider mites, and therefore do not persist in the greenhouse if pest populations are low.

Angela Madeiras, Extension Educator and Diagnostician, UMass Extension Plant Diagnostic Lab