Pear thrips (Taeniothrips inconsequens)
Western flower thrips (Frankliniella occidentalis)

Pest description and crop damage Adult western flower thrips are very small (about 0.04 inch in length at maturity), slender insects with fringed wings. They are generally white when young, but brown or black when mature. Larvae are very tiny and difficult to distinguish without magnification. Pear thrips are also very small (0.06 inch at maturity). Adults of these insects are dark and perceived as mere black specks when observed on foliage. Adult pear thrips have two pairs of wings, but are weak fliers. Consequently, dispersal by adults from one infested area to another may be attributed to wind currents. The larvae have red eyes and are pale cream to translucent green which makes them difficult to observe on host foliage. Larvae sometimes congregate in groups on the foliage which makes them more conspicuous. Western flower thrips is usually not a problem in pear, however they will enter blossoms at the full pink stage to feed on pollen, nectar, and flower parts; eggs are laid in the flower parts causing oviposition scars. Feeding by pear thrips causes blasting of buds and ragging of foliage. This pest has recently become a localized problem in the Mid-Columbia fruit-growing area, especially in orchards that border habitat with native hosts such as maple and other deciduous trees.

Biology and life history Western flower thrips overwinter as adults in ground duff. Thrips usually emerge early, about popcorn stage. In the spring they seek out flowers where they feed on pollen and nectar and lay eggs into floral parts. The larvae feed on flowers, buds and leaves. When mature, the larvae drop to the ground and pupate. The adults that emerge may lay eggs on developing fruit. Under favorable conditions, a complete life cycle may be completed in two weeks. There are several overlapping generations per year. Seasonal migration occurs at various times of the year due to destruction or drying up of host plants, and adjacent crops may be invaded by these insects. Western flower thrips eat pollen and nectar from a wide range of plants (at least 244 species from 62 families).

Pear thrips are a native of Europe and have been a pest since the early 1900s on not only tree fruit but an array of forest trees. This pest spends most of the winter as an adult female in the soil. Adults emerge in early spring and disperse to a suitable host and crawl beneath a swollen bud scale to feed on immature tissue, which they can extensively damage. Eggs are laid soon after a suitable host is located. Following egg hatch, the larvae continue to feed while the adult thrips die off. The larvae drop to the soil in late spring and prepare to overwinter.

Pest monitoring Use a beating tray during pink stage to monitor and detect immigrating pear thrips along border rows of orchard.

Management-cultural control

Western flower thrips may be reduced by removing as many broadleaf flowering plants as possible from the vicinity of the trees, as this provides an alternate host. Grass groundcovers around the trees provide competition for clovers and winter annuals that are alternate hosts.

Management-chemical control: HOME USE

  • Acetamiprid-Toxic to bees.
  • azadirachtin (neem oil)-Products containing neem extract may be phytotoxic to some pear cultivars. Some formulations are OMRI-listed for organic use.
  • bifenthrin-Highly toxic to bees.
  • carbaryl-Highly toxic to bees.
  • gamma-cyhalothrin-Highly toxic to bees.
  • imidacloprid-Highly toxic to bees.
  • insecticidal soap-Some formulations are OMRI-listed for organic use.
  • kaolin-Applied as a spray to leaves, stems, and fruit, it acts as a repellant to some insect pests. Some formulations are OMRI-listed for organic use.
  • lambda-cyhalothrin-Highly toxic to bees.
  • malathion-Highly toxic to bees.
  • permethrin-Highly toxic to bees.
  • plant-derived essential oils-Some have shown efficacy against thrips. Some formulations are OMRI-listed for organic use.
  • pyrethrins (often as a mix with other ingredients) -Highly toxic to bees. Some formulations are OMRI-listed for organic use.
  • spinosad-Some formulations are OMRI-listed for organic use.
  • zeta-cypermethrin-Highly toxic to bees.

Management-chemical control: COMMERCIAL USE

Growing-season sprays:

  • spinetoram (Delegate WG) at 4.5 to 7 oz/A. REI 4 hr. PHI 7 days. Control of thrips may be improved by addition of an adjuvant to spray mix. Do not make more than three applications of Group 5 insecticides (spinosad and spinetoram) for thrips in a season.
  • spinosad (Entrust SC) at 6 to 10 fl oz/A. REI 4 hr. PHI 7 days. Do not exceed 29 fl oz/A per year. OMRI-listed for organic use. Do not make more than three applications of Group 5 insecticides (spinosad and spinetoram) for thrips in a season.