Thrips of the British Isles

Thrips biology

Most non-taxonomic studies of thrips are aimed at the control of the small number of species that are economic or nuisance pests. Because these species mostly belong to a single Family, Thripidae, and as a group are unrepresentative of thrips in general, this can have the effect of distorting our overall understanding of the Order Thysanoptera. However, about 50% of the approximately 6180 described Thysanoptera species worldwide are mycophagous and found on dead wood or in leaf litter. These thrips are found primarily in the warmer parts of the world, largely reflecting the fact that nearly half of all thrips species are found within a single, mostly tropical and sub-tropical, Family, Phlaeothripidae (ThripsWiki, 2018). By contrast, in the British Isles, the Phlaeothripidae accounts for less than a quarter of the recorded species. Phytophagous species dominate in the British Isles, with a few predatory species concentrated in the genus Aeolothrips. These appear to be largely facultative predators of small arthropods found in flowers, though Aeolothrips albicinctus is most likely to be an obligate predator at the base of grasses.

The larvae of most species of Terebrantia, as well as phytophagous phlaeothripid species in genera such as Haplothrips and Liothrips, live and feed in flowers or on leaves. Phytophagous thrips feed by inserting their mouthparts into plant issue and sucking out the contents of individual cells of flowers, including pollen grains, or leaves or developing fruit (Kirk, 1996). Fungal-feeders in the Phlaeothripidae separate into those species that feed on fungal hyphae (the mycophagous species in the sub-family Phlaeothripinae) or those that imbibe whole fungal spores though broadened maxillary stylets (sub-family Idolothripinae).

The life cycle of a thrips consists of egg, two actively feeding larval stages, two (Terebrantia) or three (Tubulifera) non-feeding stages (propupa and one or two pupal stages) and adults that are usually macropterous, but may be micropterous or apterous. Most species in the Terebrantia use a serrated ovipositor to cut into plant tissues and insert their eggs below the plant surface; in these species, pupation commonly occurs in the soil. In the Tubulifera, eggs are laid through an extrusible chute-like ovipositor that emerges at the base of the tube, the modified tenth abdominal segment. Tubuliferan eggs are thus deposited onto the surface of the plant or fungus substrate; among these species pupae are usually found together with the larvae and adults.

Sexual dimorphism is common. Males of Terebrantia are usually smaller than females. In the fungus-feeding Phlaeothripidae, males are not only often larger than females, but can show differential allometric growth patterns associated with the size of their fore legs, and associated tubercles or fore-tarsal teeth. This appears to be an adaption to competitive sexual behaviour between the males (e.g., Crespi, 1986).

Many thrips are positively stimulated by close contact, a behaviour known as thigmotaxis. This can lead to species such as Limothrips cerealium becoming nuisance pests, crawling into the small spaces found in photographic frames and smoke detectors or fire alarms (Cuthbertson, 1989).

A more detailed overview of various aspects of thrips biology is provided by Lewis (1996).