Family: PHLAEOTHRIPIDAE

 

At least 3000 described species are currently listed in the family Phlaeothripidae, with large numbers of species remaining undescribed in the warmer parts of the world. The family is most diverse in the wet tropics, and least diverse in temperate areas. It does not extend so far North, nor so far South, as the Thripidae. The adults have simple emergent sense cones on antennal segments III & IV, the number of antennal segments usually being 8 although in some species two, three or even four segments may be fused. The forewings lack longitudinal veins, the marginal cilia do not arise from sockets, the only long setae are at the base, and the surface has no microtrichia. In many species the adults of one or both sexes are wingless. Females have a chute-like ovipositor that is retracted internally when not in use, and the tenth abdominal segment of both sexes is tubular with the anus terminal and surrounded by a ring of setae. The life cycle comprises the egg, two larval instars that feed actively, followed by three pupal instars that do not feed, and then the adults.

In contrast to the Thripidae, very few Phlaeothripidae are known as crop pests, and none is known to vector one of the tospoviruses. The generic classification is very difficult because many species are polymorphic, this variation being in part sexual and in part associated with body size. As a result, in many species of this family it can be difficult to establish that a very small male and a very large female actually belong to the same genus. Two subfamilies are recognised, the Idolothripinae and the Phlaeothripinae.


Subfamily IDOLOTHRIPINAE

About 600 species are recognised in this subfamily, in about 80 genera (Mound & Palmer, 1983). These species all feed on fungal spores, and in order to draw these into the body the maxillary stylets are unusually broad, 5 - 10 microns across. Some species, such as those in the genus Elaphrothrips, have a group of stout spine-like projections in the fore gut that function to crush the fungal spores. Large males commonly exhibit patterns of allometric growth, such that they may look very different in structure from small males of the same species. Such species are known to have complex behaviour patterns involving male/male competition and egg guarding (Crespi, 1993). These big thrips fly actively in warm weather, and single individuals may then be found on a crop or in a trap associated with a crop, but they are not pests.


Subfamily PHLAEOTHRIPINAE

With at least 2500 species and 350 genera, this subfamily is exceptionally difficult to understand. This is due partly to intrinsic problems posed by the insects, and partly to the scientifically inadequate approaches to these problems by many authors. The patterns of variation within many species are complex, both between large and small individuals as well as between the sexes. Despite this, many species have been described on one or few specimens with little or no biological information, thus giving rise to a subsequent high level of synonymy. Much of the structural variation within species is now known to be associated with intraspecific competition for resources, including male/male fighting (Crespi 1993) or female protection of a suitable living space (Crespi & Mound, 1997).

Various attempts have been made to recognise smaller families within this group (Bhatti, 1992), but the number of intermediate forms that can be found suggest that this is neither practical nor a satisfactory reflection of relationships (Mound & Marullo, 1997). In broad terms, three major lineages may be recognised within the subfamily (Mound & Marullo, 1996). The Haplothrips-lineage comprises species largely breeding in flowers, but with many species on leaves in the Oriental Region. These species have the forewings constricted medially, and the prosternal basantra are well developed. The Liothrips-lineage includes a wide range of leaf-feeding species, in which antennal segment III has one sense cone and segment IV has three sense cones, the basantra are not present, and the forewings are parallel-sided. The largest and most diverse group is the Phlaeothrips-lineage of fungus-feeding species, and it is these that show the most complex patterns of structural variation within and between species.


         

Haplothrips aculeatus

Elaphrothrips denticollis

(male, head and pronotum)

Stephanothrips occidentalis