Thysanoptera Biodiversity in the Neotropics

Rev. Biol. Trop. 50(2): 477-484, 2002 www.ucr.ac.cr www.ots.ac.cr www.ots.duke.edu INVITED PAPER MINIREVIEW Thysanoptera biodiversity in the Neotropics Laurence A. Mound CSIRO Entomology, GPO Box 1700, Canberra ACT, Australia. e-mail: [email protected] Received 20-X-2001. Corrected 12-III-2002. Accepted 14-III-2002. Abstract: It is suggested that descriptive taxonomy of thrips must be integrated into biological studies if we are to understand patterns of evolutionary and ecological diversity. Collecting and describing new taxa is easy, but understanding their position in ecosystems and how they have contributed to the origin and maintenance of biological diversity is more important yet more difficult. Many authors fail to appreciate that individual thrips species are commonly highly polymorphic, both within and between sexes, with the result that 20% of species names and 30% of generic names are currently placed into synonymy. The biological significance of such polymorphism has been little studied, but the presence of large and small males in a species is presumed to indicate some form of male/male competition for resources; this is particularly common in fungus feeding species. Amongst phytophagous species, the recognition of the host plants on which thrips actually breed is a prerequi- site to understanding patterns of diversity, some thrips lineages being associated with particular groups of plants whereas others exploit a diverse range of plants. Attempts to understand the diversity of thrips, including the application of cladistic methods, are severely limited by the lack of studies on the biology of individual species, although thrips exhibit a wide range of interesting biological phenomena, including various levels of sociality, gall-induction, specific pollination associations, virus transmission, and ectoparasitism. Key words: taxonomy, morpho-species, polymorphism, collaborative studies. Biological diversity can be considered in Thysanoptera are particularly diverse in two different ways. Taxonomists consider the the Neotropics, with considerably more than numbers and distributions of taxa, whereas 2000 species existing in this Region (Mound ecologists consider the many ways in which and Marullo 1996). These species feed on a taxa depend on each other – their biological variety of substrates, up to 50% being and behavioural relationships. Taxonomy is mycophagous either on spores or on hyphae, a thus seen as being limited to ‘product’, the large number feeding primarily in flowers, publication of descriptions, whereas most rather fewer feeding only on leaves, even on research biologists are concerned essentially mosses and ferns, with a few species predato- with ‘process’, how organisms live. If we are ry. In addition to this wide range of feeding to develop an understanding of the functioning habits, the biologies exhibited by these insects and origins of the rich biological diversity of include various levels of sociality, remarkable the Neotropics, we need to explore the com- structural polymorphisms within and between mon ground between product and process. sexes, gall-induction on leaves, specific polli- This article is a brief review of the current state nation associations, and virus transmission on of our knowledge of the insect order crop plants. One recent study has even demon- Thysanoptera, the thrips, considering both tax- strated ectoparasitism by a thrips species on an onomic products and biological processes, Homopteran (Izzo et al. 2002). Despite this with particular emphasis on the Neotropical range of interesting topics, the vast majority of region. studies on thrips in the Neotropics have been 478 REVISTA DE BIOLOGÍA TROPICAL limited either to insecticide trials or to descriptions. Thus the number of taxon descriptions is tive taxonomy. not a good measure of our knowledge of biological diversity, particularly when, as in some groups, up to 50% of names fall as synonyms, OBJECTIVES OF TAXONOMY and high synonymy rates remain a modern methodological, not merely an historical, arte- Descriptive taxonomy is essentially sub- fact (Gaston and Mound 1993). jective, museum taxonomists rarely testing the In contrast, an apparently similar ques- veracity of the hypotheses they erect, these tion, “Why are there so many species of being the new species that they describe insects?” resonates through most biological (Gaston and Mound 1993). As a result, many disciplines. It involves comparative studies biology students avoid taxonomy, even when between species and the ways in which they recognizing that biological observations need share available resources. It involves species to be viewed in a comparative, evolutionary, turnover between localities (Bartlett et al. framework. This has led to an increasing lack 1999), habitats and seasons, and thus requires of taxonomic specialists over the last 30 years, information on how species disperse, and how and this in turn limits the range of biodiversity they exploit ecosystems that are in a constant questions that can be asked. For example, in state of flux. This one question thus subsumes tropical forests, neither the ecology of tree so many other questions that are fundamental flowers, nor the dynamics of leaf-litter sys- to understanding how biological diversity has tems, can be studied in depth, due to the lack arisen, and how we will conserve it. The ques- of taxonomic expertise for many of the insect tion “Why?” is about process and opens up groups involved. Molecular technology is new avenues of thought; the question “How broadening the interest in taxonomy, such tools many?” is about product and, by itself, is of being seen to provide more objective methods more political than scientific interest. for examining relationships between taxa. But the lack of defined objectives for descriptive taxonomy remains a problem, both for attract- THRIPS SPECIES-LEVEL ing new students and for funding the long-term TAXONOMY AND BIOLOGY employment of specialists. The lack of clarity in taxonomic objec- Almost 5 500 species of Thysanoptera are tives is curious (Mound 1998). The question currently considered valid worldwide, in nine “How many species of insects are there?” is families and almost 750 genera. Judging from deceptively attractive, and has received con- material in the major museum collections siderable attention in recent years. Suggestions there are probably about 10 000 thrips species have been made that funding be sought to in the world. The total number of described describe all of the world’s taxa (Anonymous species from Central and South America is 1994). Even if we assume that a precise answer about 1 600 (Mound and Marullo 1996), and to this question is possible, the use that could more than 700 species of thrips have been be made of that answer to generate further sci- described from Brazil. This latter figure sug- entific questions is not clear. Probably as many gests that the thrips fauna of Brazil is quite as 50% of named insect species are based on well known, in that a good proportion of the single samples, even single individuals, with species have been given names. But few of little known either of their biology or their these species can be recognized from the litera- variation. Moreover, probably 5% of named ture, and little is known about how most of insect species are known only from unrecog- them live, beyond that some are probably fun- nizable, although not necessarily old, descrip- gus-feeding, or grass-feeding or flower-feeding. INTERNATIONAL JOURNAL OF TROPICAL BIOLOGY AND CONSERVATION 479 Problems in descriptive taxonomy Mexican biodiversity, particularly the inter-relationships of this important tree crop with the Describing large numbers of species is not native flora and fauna. In this instance, each simple. For example, more than 150 species ‘new species’ was defined on trivial structural are recognized in the genus Frankliniella features that are known to be highly variable (Nakahara 1997), 120 of these being known within several pest species of Scirtothrips. In from the Neotropics. However, in the collec- indicating that such taxonomic conclusions are tions of the Natural History Museum, London, unreliable, Mound and Strassen (2001) suggest- and the US National Museum, Washington, ed that taxonomic decisions are sometimes too there are several thousand microscope slides of important to other biologists to be left solely to unidentified Frankliniella species from the descriptive taxonomists. South American Cordillera. Most of these Some correlation presumably exists unidentified Frankliniella cannot be sorted sat- between floristic diversity and the diversity of isfactorily even to putative ‘morpho-species’, plant-feeding thrips. But host plant exploita- because we are unable to distinguish securely tion by thrips ranges from strict monophagy to between patterns of intra- and inter-population extensive polyphagy, often within genera. variation. For many, even males and females Thus two species of Echinothrips are known to cannot be associated satisfactorily, due to be strict monophages, on Tsuga and on colour differences between sexes and structur- Selaginella, whereas a third member of the al differences between large and small individ- genus is a pest on a wide range of plants in uals. It is not unusual to find adults of two or greenhouses (Collins 1998). In the genera more species of Frankliniella in the same set Frankliniella and Scirtothrips, a few species of flowers. To establish the intraspecific varia-

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