Thrips and plants
Laurence A. Mound, CSIRO Ecosystem Sciences, Canberra
All thrips are dependent on plants in some way. However, more than 50% of thrips species live only on dead plants where they feed on fungi, and some thrips species are predators of mites or other small arthropods on living plants. The fungus-feeding thrips live in leaf-litter and on dead branches, most of them feeding on hyphae or fungal break-down products, although about 600 species, the Idolothripinae, ingest whole fungal spores. Very little is known about which species of fungi are used as food by thrips, although Hoplothrips pedicularius in England is associated with the hyphae of Stereum fungi (Crespi 1986). Some larger Idolothripinae include in their gut large ovoid spores of the family Botryosphaeriaceae (Tree et al., 2010).
Thrips are commonly regarded as flower-living insects because large numbers sometimes can be seen in a flower, but precise information on the species of flowers used for breeding is available for few species. Many thrips breed only on grasses (Mound, 2011), including species of Anaphothrips and Limothrips that breed mainly on leaves, and Chirothrips and Arorathrips species that breed only within grass flowers. Species of Odontothrips and Megalurothrips breed in the flowers of various Fabaceae, and species of Aurantothrips and Dichromothrips breed on flowers and leaves of Orchidaceae. In contrast, patterns of host-plant exploitation are not evident within the largest genera of Thripidae, Frankliniella and Thrips, and some species in these genera breed on many different plants (Teulon & Penman, 1990). Some flower-living thrips are important as pollinators of their host-plant (see Thrips and pollination), but in Australia Grevillea species with red flowers are vertebrate pollinated, and visiting thrips can come to a “sticky end” among the copious nectar.
Determining the “host plant” of a thrips can be difficult, with many host records being no more than adult “finding places” of these highly dispersive insects (Mound, 2013). A particular plant may be used as a mating or feeding site, but not used for breeding. Or a species may breed on various different plants under laboratory conditions, but be host-specific under field conditions, such as Scirtothrips aurantii (Garms et al., 2013). A specific host association cannot be assumed just because large numbers of adult thrips are found on a plant. The Australian Black Plague Thrips, Haplothrips froggatti, breeds only in the flowers of grasses, but as these grasses dry in the heat of summer huge swarms of this thrips land on many different plants, including cotton on which they cannot survive for more than a very few days.
Some thrips species breed only on leaves, often on very young leaves as in the pest species of Scirtothrips. Other thrips breed on more mature leaves, such as Dendrothrips species. Some, such as Heliothrips and Selenothrips species, are associated with older, senescing leaves. Leaf-feeding is particularly common amongst Phlaeothripinae in warmer parts of the world, often involving gall-induction (see Thrips and galls). Leaf-feeding Phlaeothripinae are probably host-specific, but there have been few studies of patterns of evolutionary radiation in association with their hosts (Ananthakrishnan & Raman, 1989). In the Old World tropics, Gynaikothrips species are particularly associated with Ficus leaves, and in the arid areas of western USA, Bagnalliella species are associated with Yucca species.
In Southeast Asia, bamboo species support remarkable radiations among both Thripidae (Nonaka & Yangvitaya 1993) and Phlaeothripinae (Okajima,1993), although nothing is known of the biology of these thrips. In Australia a radiation of at least 250 Phlaeothripinae species occurs on the phyllodes of Acacia shrubs and trees, and a smaller radiation of at least ten species of Phlaeothripinae occurs on the leaves of the Rutaceae genus Geijera (Mound, 1971). On Australian Sheoak trees, the species of Casuarina, there is a radiation of remarkable Phlaeothripinae with elongate and sometimes convoluted feeding stylets (Mound, 1971), as well as gall-inducing and kleptoparasitic species in uniquely woody galls (Mound et al., 1998).
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Crespi BJ (1986) Territoriality and fighting in a colonial thrips, Hoplothrips pedicularius, and sexual dimorphism in Thysanoptera. Ecological Entomology 11: 119-130.
Garms BJ, Mound LA & Schellhorn NA (2013) Polyphagy in the Australian population of South African citrus thrips (Scirtothrips aurantii Faure). Australian Journal of Entomology 52: 282-289.
Mound LA (1970) Convoluted maxillary stylets and the systematics of some Phlaeothripine Thysanoptera from Casuarina trees in Australia. Australian Journal of Zoology 18: 439-463.
Mound LA (1971) The complex of Thysanoptera in rolled leaf galls on Geijera. Journal of the Australian Entomological Society 10: 83-97.
Mound LA (2011) Grass-dependent Thysanoptera of the family Thripidae from Australia. Zootaxa 3064: 1-40.
Mound LA (2013) Homologies and host-plant specificity: recurrent problems in the study of thrips. Florida Entomologist 96(2): 318-322.
Mound LA, Crespi BJ & Tucker A (1998) Polymorphism and kleptoparasitism in thrips (Thysanoptera: Phlaeothripidae) from woody galls on Casuarina trees. Australian Journal of Entomology 37: 8-16.
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Teulon, DAJ, Penman DR (1990) Host records for the New Zealand flower thrips (Thrips obscuratus (Crawford) Thysanoptera: Thripidae). New Zealand Entomologist 13: 46-51.
Tree DJ, Mound, LA & Walter, GH (2010) Fungal spore-feeding by adult and larval Mecynothrips hardyi (Priesner) (Thysanoptera: Phlaeothripidae: Idolothripinae). Journal of Natural History 44: 307-316.