Western Flower Thrips

Western flower thrips is the most widely distributed thrips species, occurring throughout all olive-growing districts in California. It has a wide host range, feeding on grasses, field and forage crops, vegetables, and fruit crops.

Western flower thrips are tiny insects about 0.05 inch (1 mm) long, with two pair of fringed wings. Adults vary in color from white to yellow with slight brown spots on the top of the abdomen, to yellowish with an orange thorax and brown abdomen, to completely dark brown. Different color forms predominate according to the time of year.

Eggs are inserted into leaves, flower parts, and fruit. First-instar nymphs are light yellow, turning golden yellow after the first molt. When they are ready to pupate, nymphs drop to the ground and pupate in protected places.

Western flower thrips migrate into olives after adjoining grasses dry up in spring, causing serious damage to fruit. Ascolano is most susceptible, although other cultivars can be damaged. Developing fruit is scarred and dimpled by thrips feeding. Damaged fruit is culled before processing. Olive groves adjoining drying grain fields are most susceptible to damage.

Managing vegetation in and around olive groves is important in reducing the potential for damage from western flower thrips. Avoid discing orchard cover crops while trees are in bloom. Disc open areas adjacent to groves as early as possible to prevent thrips' development and migration to olive trees. There is no current California registration for any chemical treatment. In years when this pest is particularly damaging and a special local need registration is approved, apply treatments at full bloom if thrips are migrating to olives and their presence has been noted in the bloom.