BIOLOGICAL CONTROL AGENTS FOR THRIPS

Orius insidiosus (Pirate bug)

Orius insidiosus is a small predatory 'true' bug. The adults are 2.5–3 mm long, with a dark brown/black head and thorax and distinctively patterned black and white forewings. The eggs are laid in plant tissues (often near the growing tips) and there are five nymphal (immature) stages, all of which are predatory. First instar nymphs are approximately 0.5 mm long and pale yellow; subsequent nymphal stages become progressively darker, with the final two stages being tan to dark brown. As in other species of Orius, the nymphs have red eyes.

This species is a generalist predator with a preference for thrips (particularly western flower thrips). Young nymphs of O. insidiosus will feed on immature thrips, while adults will attack both adults and immatures. This species will also feed on various other pests (including spider mites, moth eggs/small larvae and aphids), as well as on pollen. This ability to feed on alternative food sources helps maintain the pirate bug population even when thrips are scarce.

The life cycle (egg to adult) can be completed in 13 days at 28 °C (82 °F) and in approximately 20 days at 24 °C (75 °F). Development and activity is considerably slower at 20 °C (68 °F). 

It is important to note that under short-day conditions and cooler temperatures, this species will enter 'reproductive diapause', during which egg-laying is suspended. The onset and termination of diapause are influenced by both temperature and day length: for example, at 18 °C (64 °F), the critical day-length is approximately 10-11 hours, while at 20 °C (68 °F), the critical day-length lies between 12 and 13 hours. Diapause can be avoided by increasing the temperature and/or by using supplemental lighting to increase day length.

Orius insidiosus is available in shaker bottles containing 500, 1000, or 5000 adults.

Neoseiulus cucumeris (formerly known as Amblyseius cucumeris)

Neoseiulus cucumeris is a generalist predatory mite that attacks the immature stages of several species of thrips (including western flower thrips and onion thrips (Thrips tabaci)) as well as various plant-feeding mites (e.g. broad mite (Polyphagotarsonemus latus) and cyclamen mite (Phytonemus pallidus); it will also feed on pollen, particularly when prey is scarce. This species has a tendency to feed on the most readily available prey, and higher release rates may be advisable if several potential prey species are present.

The adult mites are approximately 0.5 mm in length and look similar to several other species of Neoseiulus, with somewhat pear-shaped, pale beige to pale brown bodies. The small oval eggs are typically laid close to the main veins on the undersurface of leaves, or amongst leaf hairs. 

The six-legged larva that emerges from the egg does not feed and is relatively sedentary, but the remaining two immature stages (the 8-legged protonymph and deutonymph) are more mobile and will attack first instar thrips nymphs. Older nymphs of most thrips species are too large to be attacked, and adult thrips are not consumed. For this reason, N. cucumeris is best introduced when thrips numbers are low; do not expect to see a noticeable reduction in adult thrips until approximately 3 weeks after introduction (depending on temperature). 

Optimum temperatures for this species are 20–25 °C (68-77 °F), with relative humidity in the range of 65–75%. At temperatures of 30 °C and above, the immature stages become increasingly sensitive to reductions in humidity, with the newly hatched larval stage being particularly vulnerable. The life-cycle (egg to adult) can be completed in approximately 8–10 days at 25 °C, with adults living up to about 30 days. Commercial strains generally do not enter diapause; however, egg-production tends to be lower under reduced light intensity and at cooler temperatures.

Neoseiulus cucumeris is available in a wide variety of product types, ranging from different designs of sachets to shaker tubes and bulk bags. Depending on formulation, numbers per pack (mixed life-stages) range from 20,000 to 500,000. Please contact us for further details.

Iphiseius degenerans (formerly known as Amblyseius degenerans)

This predatory mite is similar in shape to related mites (such as Neoseiulus cucumeris), but differs in being a conspicuous, shiny, dark brown/black rather than pale beige/tan; the adults are approximately 1 mm long (slightly larger—and more active—than those of N. cucumeris). Iphiseius degenerans is considered to be a specialist predator of thrips larvae, but will also help suppress whiteflies and spider mites. It has been reported to feed on both first and second instar thrips, whereas N. cucumeris prefers first instars.

Like various other predatory mites, I. degenerans also feeds on pollen, but its affinity for flowers is unusually strong, making it ideally suited for control of various species of flower thrips (including the Western flower thrips (Frankliniella occidentalis)) in fruiting crops such as sweet peppers. In such crops*, this affinity for flowers allows populations of I. degenerans to rapidly increase and sustain themselves on pollen even if prey are scarce. In this way, the crop itself can serve as an in situ ‘nursery’ for producing more of these predators; hence it is best to introduce this species on a preventative basis soon after flowering commences. As populations increase, the mite will gradually disperse throughout the crop, and will be found on both flowers and leaves (where it lays its eggs).

The optimal temperature for this species is reported to be around 77 °F (25 °C), although it will tolerate higher temperatures and relatively low humidity. At 77 °F (25 °C), the life cycle (from egg to adult) is completed in approximately 7 days, with each female producing about 60 eggs over an adult lifetime of 4–6 weeks. 

The eggs are typically laid on the underside of leaves, close to the main vein (or junctions between leaf veins), or under curled leaf margins. In particularly favorable sites, females may lay eggs on top of those deposited earlier, either by themselves or by other females. In this way, quite large egg clusters may accumulate – a distinctive feature of this mite.

*Please note that, unless supplemental pollen is provided, this species is less suitable for non-flowering or late-blooming crops, as it cannot be reared on bran mites and hence is not available in large quantities at prices that allow multiple augmentative releases. It is also known to be quite sensitive to various insecticides and fungicides—including sulfur vapor used for powdery mildew management.

Iphiseius degenerans is available in 30 ml plastic tubes of 500 individuals in a vermiculite carrier.

Amblyseius swirskii 

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