While visual inspection of blooms, fruit and foliage is a necessity in field crops, this is not practical in all cropping situations. In transplant production facilities, handling plant material must be minimized to avoid spreading plant disease pathogens. In such situations, water pan or sticky trapping is a viable alternative to visual inspection for monitoring populations of thrips and other insects. Yellow sticky traps are especially useful because they attract several important insect pests, including not only thrips but aphids, leafminers and silverleaf whiteflies. While blue or white sticky traps have been shown to be more attractive to some thrips species, notably the Florida and western flower thrips (Childers & Brecht 1996, Gillespie & Vernon 1990, Yudin et al. 1987), yellow traps may be the better choice because of their greater utility.
A major drawback in the use of sticky traps is windblown dust or plant debris. In such situations where these are likely to occur, the use of water pan traps should be considered. Water pan traps have an added benefit in that the contents of distant traps can be shipped in water tight containers, preserving the trapped insects in good condition. Shipping used sticky traps is usually unsatisfactory, because of the risk of specimen damage from other traps or packing material. Water pan traps should be made of shallow containers, 1.5-2 inches deep, of an attractive color, preferably white or yellow. Adding a few drops of dishwashing detergent or other wetting agent to a gallon of water used to fill the pan reduces the surface tension and allows small insects to sink rather than becoming trapped on the surface. For traps that remain in the environment a few days between collections, adding a tablespoon of rocksalt to each trap will slow the deterioration of the specimens.
Removing trapped thrips from sticky traps and water pan traps can be tedious. If thrips from sticky traps are to be identified to species, this can only be done after the glue has been removed. Carefully lifting the specimen with some of the glue from the trap with a toothpick, and soaking it in turpentine or mineral spirits is the easiest way to accomplish this.
Removing thrips from water pans is much easier. Large insects and other debris are removed by pouring the trap contents through a coarse kitchen strainer into a bowl or spouted cup. The strained contents are then poured through a fine strainer (120 mesh). The insects caught in the fine strainer can be washed to the center of the strainer under running water. The strainer is then inverted over a shallow dish containing alcohol, and dipped into the alcohol until all specimens are in the dish. The specimens are then ready for examination under a dissecting microscope.