Botanical Journal of the Linnean Society, 2006, 152, 109–130. With 20 figures © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society, 2006, 152, 109–130 109 Blackwell Publishing LtdOxford, UKBOJBotanical Journal of the Linnean Society0024-4074The Linnean Society of London, 2006? 2006 1521 109130 Original Article LEAF MORPHOLOGY AND HOST SELECTION BY THRIPS A. S. SCOTT BROWN and M. S. J. SIMMONDS *Corresponding author. E-mail: a.scott-brown@rbgkew.org.uk Leaf morphology of hosts and nonhosts of the thrips Heliothrips haemorrhoidalis (Bouché) ALISON S. SCOTT BROWN* and MONIQUE S. J. SIMMONDS Royal Botanic Gardens, Kew, Surrey, TW9 3AB, UK Received August 2005; accepted for publication March 2006 This study highlights the morphological differences between two groups of plants; those that are recorded as hosts of the thrips Heliothrips haemorrhoidalis (Bouché) and those that remain free from infestation. Scanning electron microscope techniques were used to describe the morphology of the leaf surface of 19 species in order to help identify which morphological features could play a role in the selection of plant species by thrips from among a diverse botan- ical collection. H. haemorrhoidalis had a preference for species with leaves that were coriaceous, with one or both surfaces being smooth. Plants evading these thrips commonly possessed glandular trichomes. Thus morphology may have a role in deterring thrips from the leaf surface, as well as influencing the behaviour of predators that control thrips. Further detailed studies into the chemistry of leaves of hosts and nonhost species may help to further our understanding of selection mechanisms. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society, 2006, 152, 109–130. ADDITIONAL KEYWORDS: Leaf surface morphology – plant/insect interactions – thysanoptera. INTRODUCTION A wide range of plant species are susceptible to inva- sive thrips, such as Heliothrips haemorrhoidalis (Bouché) (Thysanoptera: Thripidae) (Fig. 1A), but the factors that influence the host selection behaviour of these insects are not well studied. H. haemorrhoidalis is often documented as causing widespread damage to economically important plantation crops such as avo- cado (Goodall et al., 1987; Dennill & Erasmus, 1992) and citrus (Holt, 1989) but in Britain it tends to be confined to interior plantscapes and protected orna- mentals. H. haemorrhoidalis pose a threat to the botanical collections contained in the glasshouses at the Royal Botanic Gardens, Kew (RBG Kew) and are able to discriminate among the highly genetically and phenotypically diverse species, infesting some species but not others (Scott Brown, 2001). Primary damage to plant hosts is caused by thrips feeding on the con- tents of epidermal cells of leaves and fruit of hosts (Heming, 1993) and through the process of oviposition where eggs are embedded in the epidermal tissue. Levels of injury vary from a slight ‘silvering effect’ on the surface of leaves and fruit of hosts (Fig. 1B), to the complete desiccation of leaves and subsequent defoli- ation of species which have low tolerance to high thrips infestation levels. H. haemorrhoidalis still per- sist on susceptible plant species in the glasshouses at RBG Kew despite the introduction of an Integrated Pest Management (IPM) strategy using predators that are employed successfully to control thrips on many protected monocrops (Bennison, 1988; Ramakers, 1988; Gillespie, 1989; Bennison & Jacobson, 1991; Tavella, Arzone & Alma, 1991; Houten & Stratum, 1995). Numerous studies suggest that plant defences, both morphological and chemical, directly affect the selection of hosts by herbivorous insects such as thrips. Plant morphological defences include hairs or trichomes (Lenteren et al., 1995; Pfannenstiel & Year- gan, 1998), crystals (Ruiz, Ward & Saltz, 2002), Silica (Djamin & Pathak, 1967; Hanifa, Subramaniam & Ponnaiya, 1974; Moore, 1984), waxes and toughened cuticle (Stevenson et al., 1993). Chemical defences include production of toxic and repellent compounds as well as compounds that influence food utilization in herbivorous insects (Schoonhoven, Jermy & van Loon, 1998). Such characteristics may further indirectly Downloaded from https://academic.oup.com/botlinnean/article-abstract/152/1/109/2420263 by guest on 28 May 2020