Scouting for thrips in vegetable crops requires great attention to detail. The technique the scout will use depends heavily on:

Some general considerations include the following:

The Influence of Weather

Weather obviously has a major impact on thrips. In areas where freezing temperatures occur, thrips populations will appear with the first warm weather of the spring, usually coinciding with the return of blooms to wild hosts. Where temperatures are mild throughout the winter, thrips may be encountered throughout the year. However, their number will vary according to the availability of alternate hosts.

Rain is also influential. Thrips can be adversely affected by heavy rains, as their moisture sensitive pupal stage occurs in the soil. During dry periods, thrips numbers may be somewhat reduced if host plants have reduced thriftiness. However, as many vegetable fields and surrounding crops are irrigated, the effect of low rainfall may be minimal. An interesting observation involving Frankliniella bispinosa in Florida is that massive flights often occur shortly after brief spring showers. Whether this is due to changes in convection and air turbulence, the thrips being dislodged from their wild host blooms, or to some host-seeking behavior triggered by the rain may be a good research topic!

Presence of Tomato Spotted Wilt Virus

Scouts need to be aware of the prevalence of this thrips-borne virus disease in the geographical vicinity of the scouted fields. If a field is near a crop, such as peanuts, which is known to serve as a reservoir for tomato spotted wilt virus (TSWV), scouting will need to be much more intense than in areas where reservoirs do not exist. This extra effort will be necessary throughout the life of the crop, as infection can be started not only by flower-feeding thrips, but by those feeding or probing on the foliage as well. In areas where TSWV is likely to occur, scouts should familiarize themselves as early as possible with the field identification characteristics as well as the feeding habits of the local thrips species.

Crop Type

Fruiting crops such as peppers and eggplants will require close examination of their blooms. The use of a 10x hand lens is recommended when examining blooms, as thrips larva often lodge themselves into the tight areas around the bases of stamens. This behavior, along with their small size and pale color, makes thrips larvae particularly difficult to see without magnification. If thrips larvae are found in blooms in such crops, scouts should examine the calyx area of newly formed fruits for larvae.

Neighboring Crops

The thrips infesting a particular field are not the only ones of concern to a scout. a good scout should be aware of the thrips infesting surrounding crops as well. This is particularly true where alternate hosts of TSWV or its vectors are grown, or where alternate hosts of highly damaging species, such as melon thrips, are destructively harvested. Destructive harvesting of snap beans probably played a major role in the melon thrips disasters of the early 1990's in Homestead, FL. On a smaller scale, moving melon thrips-infested eggplants or peppers (fruit, foliage) at the end of harvesting, has led to significant damage in nearby fields of newly planted peppers and cucurbits. The take-home message for growers and vegetable scouts is "Be aware of what is going on around the fields you scout!"