THRIPS

INTRO:
Thrips are small, slender and winged insects. They feed by puncturing the outer layer of host tissue and sucking out the cell contents, resulting in stippling, streaky flecking, or silvering of the leaf surface. Thrips which feed on plants tend to damage the whole appearance of the plant in conjunction, so the leaves, stems and fruit.

IDENTIFICATION:
Most adult thrips are long, slender, minute, and have fringes on the margins of both pairs of their narrow wings. The larvae are oblong or slender and elongated, but lack wings. Most thrips are semi-transparent white or yellowish or dark brown to black. It is more important to distinguish among thrips species in situations where integrated pest management methods are used. For example, each species of natural enemy preys on and helps to control certain species of thrips or other pests. Certain thrips occur on many different plants but damage only a few of the plant species on which they are found.

LIFE CYCLE
Thrips hatch from an egg and develop through two actively feeding larval stages and two non-feeding stages, the prepupa and pupa, before becoming an adult. Female thrips lay their eggs in leaf tissue where the larvae will feed. Thrips have numerous generations in a year. When the weather is warm it takes only 2 weeks for the egg to mature into an adult.

DAMAGE
The damage to the plants due to thrips feeding harms its fruit, leaves, and shoots. The leaves become unhealthy and tend to drop off once it becomes papery and distorted. Thrips create silvery lesions with black flecks (frass) on leaves and scabby scarring on the fruits, but do not take away the flavour of the fruit.

Cultural Control
Thrips are difficult to control. An integrated approach is required so that it combines the use of good cultural practices, natural enemies, and the most selective or least-toxic insecticides that are effective. Thrips species that feed on many different plant species often move into gardens and landscapes when plants in weedy areas or grasslands begin to dry in spring or summer. Keeping plants well irrigated and avoiding unwarranted applications of nitrogen fertilizer can reduce the higher growth of thrips.

Greenhouse Thrips Management
The most common thrips species in greenhouses is the Western flower thrips, which can infest many plant species. It occurs mainly on the underside of leaves and in flowers. Greenhouse thrips are sluggish and the adults tend not to move around too much. Individuals feed in groups and populations usually begin on leaves before moving to flowers.
Thrips can be suppressed in the greenhouse with systematic application of certain chemicals or foliar application of contact chemicals. Repeat applications may be necessary. Keep in mind that greenhouse thrips have natural enemies that when used appropriately can be very effective. Amblyseius cucumeris is a beige predatory mite of less than 1 mm. It is quite conspicuous because of its mobility on the underside of a leaf or in the flower. The female mite mates several times and deposits a few eggs daily on leaf hairs close to the veins on the underside of the leaf. An adult cucumeris can live up to 3 weeks.

Adult cucumeris pierce their prey and suck them empty. Also, they eat pollen which is an interesting characteristic for preventative introduction of Amblyseius cucumeris in pollen bearing crops such as sweet pepper and eggplant. A. cucumeris has been in use for years in several greenhouse vegetables crops such as sweet pepper and eggplant.

Amblyseius swirskii is a prized predatory mite widely used around the world. This species is considered a generalist predator, and freely ingests small soft-bodied pest species as well as pollen or plant exudates. Amblyseius swirskii has attracted substantial interest as a biological control agent of thrips in greenhouse and nursery crops, and is currently reared and sold commercially for this purpose. In addition to insect prey, swirskii can survive and reproduce on various pollens and gain sustenance from plant nectars, which may allow them to persist during periods of low pest density and improve their effectiveness as biological control agents. Swirskii is adjusted to warmer and humid sub-tropical climates and is effective year-round, as it does not diapause.

Amblyseius swirskii is known to feed and reproduce on a wide range of thrips, western flower thrips, onion thrips, and chilli thrips, etc. Swirskii is commonly used to control whitefly and thrips in greenhouse vegetables, like cucumber, pepper and eggplant, and is often used instead of cucumeris due to its more aggressive nature.