Host plant toxicity affects developmental rates in a polyphagous fruit fly: experimental evidence NATHALIE ERBOUT 1,2 *, MARC DE MEYER 3 , CARL VANGESTEL 1 and LUC LENS 1 1 Department of Biology, Terrestrial Ecology Unit, Ghent University, Ledeganckstraat 35, B-9000 Ghent, Belgium 2 Environmental Health Division, International Centre of Insect Physiology and Ecology, P.O.Box 30772-00100 Nairobi, Kenya 3 Entomology Section, Royal Museum for Central Africa, Leuvensesteenweg 13, B-3080 Tervuren, Belgium Received 9 December 2008; accepted for publication 14 January 2009 Various, non-exclusive mechanisms have been invoked to explain the observed association between host plant use and speciation in insect species. In the Afrotropical genus Ceratitis (Diptera: Tephritidae), morphological, molecu- lar, and biochemical data suggest that evolutionary radiation of stenophagous clades originates from their ability to exploit toxic hosts. To test whether, and to what extent, the development and fitness of Ceratitis fasciventris,a polyphagous congener known to infest over 43 host species, is adversely affected by host plant toxicity, we compared the rates of development, survival, and reproduction of captive bred individuals in four media that differ in alkaloid concentration. Despite reduced pupal and adult sizes, C. fasciventris larvae developing under low alkaloid concentrations successfully developed to the adult stage, probably as a result of accelerated pupation and ensuing restricted exposure to the toxic environment. High alkaloid concentrations, however, impaired their developmental process and prevented subsequent reproduction. The adverse effects of host plant toxicity on larval development in polyphagous fruit flies indicate that high alkaloid concentrations pose a significant constraint on host use by polyphagous Ceratitis species. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 728–737. ADDITIONAL KEYWORDS: Ceratitis fasciventris – fluctuating asymmetry – Solanum – stenophagy. INTRODUCTION Various, non-exclusive mechanisms have been invoked to explain the association between patterns of specia- tion and host plant use in phytophagous insects, such as shifts in (or expansion of) host plant use (Weingart- ner, Wahlberg & Nylin, 2006), hybridization (Schwarz et al., 2007), adaptive radiation (Braby & Trueman, 2006), specialization, and reproductive isolation (Schluter, 1998). A well-documented example of sym- patric speciation associated with host plant use is provided by the monophagous apple maggot fly Rhago- letis pomonella (Walsh, 1867) (Diptera: Tephritidae) (Bush, 1969; Berlocher, 1998). The sibling taxa com- prising the R. pomonella group are believed to originate from sympatric host shifts (Bush, 1966) subsequent to the introduction of new host plants [e.g. Malus pumila (Miller)] and genetic changes in key loci responsible for host plant selection and (or) plasticity in diapause length (Feder et al., 2003). Within the same taxonomic entity, the ‘Lonicera fly’ probably evolved by hybridization between two native Rhagole- tis species [Rhagoletis mendax (Curran, 1932) and Rhagoletis zephyria (Snow, 1894)] after a host shift to an introduced exotic weed (Lonicera spp.), which cata- lyzed the local breakdown of reproductive isolation between both parental species (Schwarz et al., 2007). Similar cases of speciation may have also been fascili- tated by host use in polyphagous taxa such as butter- flies (Murphy & Feeny, 2006; Mercader & Scriber, 2007), Hemiptera (Percy, Page & Cronk, 2004), and leaf-mining moths (Ohshima & Yoshizawa, 2005). *Correspondence author. E-mail: nathalie.erbout@ugent.be Biological Journal of the Linnean Society, 2009, 97, 728–737. With 2 figures © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 728–737 728