Although some thrips species are responsible for reducing crop yields, either through feeding damage or by transmitting tospovirus diseases, this is not the only way in which a thrips species can be considered a pest. For example, thrips adults have the habit of crawling into small spaces, a behavior known as thigmotaxis. This can result in these insects triggering smoke detectors and fire alarms and thus causing considerable inconvenience. This behavior also leads to thrips invading computers, watches, paintings, polystyrene building insulation, hypodermic needles in manufacture, and many other unlikely places. Similarly, the Californian bean thrips crawls into the navels of oranges; this causes no damage but results in the fruit being rejected by export markets (Hoddle et al., 2006). Thus a "pest" is not necessarily something that causes damage to a crop, but is something with the potential to damage a market.
There are several important pest thrips in California. The Californian citrus thrips, Scirtothrips citri, may have only a limited effect on yield, but the damage to the surface of fruit can seriously reduce market value. The related species on avocado, Scirtothrips perseae, can cause very severe damage to avocado fruit such that it is not suitable for sale. In the horticultural industry and among some vegetable crops the western flower thrips, Frankliniella occidentalis, can cause very severe losses, through a combination of the tospoviruses transmitted and direct feeding damage. Thus field crops of capsicums and greenhouse crops of chrysanthemums may become completely uneconomic when heavily attacked by this species. Despite this, western flower thrips can at times be considered beneficial, as when it feeds on mites that can cause severe leaf damage to cotton plants.