Leaf-mining chrysomelids 1 Leaf-mining chrysomelids Jorge A. Santiago-Blay Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA “There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.” (Act I, Scene 5, Lines 66-167) “To be or not to be; that is the question” (Act III, Section 1, Line 58) both quotes from “The Tragedy of Hamlet, Prince of Denmark” by William Shakespeare (1564-1616) Abstract into two morphological categories: the eruciform, less modi- fied type (Galerucinae and some Alticinae); and the flattened, Leaf-mining is the relatively prolonged consumption of foliar sometimes onisciform type characteristic of the Zeugophorinae, material contained within the epidermal layers, without elicit- many Alticinae, the Cassidinae, and the Hispinae. There are ing a major histological response from the plant. This type of no published data on the larval structure of leaf-mining herbivory is relatively uncommon in the Chrysomelidae and criocerines. Larval leaf-mining chrysomelids are reported to has been reported in 103 genera, representing 4% of the ap- have rather broad host-plant feeding preferences. For adults, proximately 2600 described genera and amounting to over the ranges are broader. The Index of Feeding Range (IFR) is 500 reported species, or 1-2% of the 40-50,000 described introduced herein as a scalar to quantify the feeding range of species. Larvae in the following subfamilies are known leaf- the larvae (IFRi) and adults (IFRa). For the Zeugophorinae, miners, with numbers and percentages of taxa also being in- IFRi is 2.0 and IFRa 2.9. The plant families (and genera, cluded. The subfamily Zeugophorinae consists of one genus parenthesized) most commonly reported serving as host-plants with reported leaf-mining species, or 25% of the total genera; for the Zeugophorinae are the Salicaceae (Salix and Populus), there are twelve reported leaf-mining species, about 17-20% the Betulaceae (Betula and Corylus), and the Celastraceae. of the species described in the subfamily and about 60-70 For adult zeugophorines, 55% of the reported species only described species in the Zeugophorinae, all believed to be feed on one plant genus, and 82% of the reported species feed leaf-miners. The subfamily Criocerinae comprises two genera on one plant family only. For the Galerucinae, IFRi is 1.0 and of reported leaf-miners, representing 10% of the described IFRa 2.4. The plant families (and genera, parenthesized) most genera, and two reported leaf-mining species, accounting for commonly reported serving as host plants for the Galerucinae less than 1% of the approximately 1450 species described in are the Asteraceae (several genera) and the Chenopodiaceae the Criocerinae. The Galerucinae has two reported leaf-min- (Atriplex, Chenopodium, Suaeda, etc.). For adult galerucines, ing genera, representing less than 1% of the approximately 32% of the reported species only feed on one plant genus, and 500 genera described. There are approximately 20 reported 60% of the reported species only feed on one plant family. For species of leaf-mining galerucines, accounting for less than the Alticinae, IFRi is 2.7 and IFRa (excluding the data for 1% of the approximately 7000 species described in the sub- Phyllotreta nemorum) is 3.8. The plant families most com- family. The Alticinae has nineteen reported leaf-mining gen- monly reported to be serving as host plants for the Alticinae era, representing about 3% of the approximately 500 genera are Brassicaceae, Lamiaceae, Asteraceae, Plantaginaceae, described. There are 65 reported species of leaf-mining flea- Scrophulariaceae, Polygonaceae, and Poaceae, but many more beetles, or about 1-2% of the 4000-8000 species described in families and numerous genera are reported as host plants. For the Alticinae. The Hispinae is represented by 78 genera that adult alticines, 47% of the reported species only feed on one have been reported as leaf-miners, or 40% of the approxi- plant genus, and 71% of the reported species only feed on one mately 200 genera described. There are over 400 reported plant family. For the Cryptostomes (Hispinae + Cassidinae), leaf-mining hispines, accounting for 14% of the over 3000 IFRi 1.6 and IFRa is 3.02. The plant families (and genera, species described in the subfamily. There is a single reported parenthesized) most commonly reported as host plants for the genus of leaf-mining in the Cassidinae, representing less than Hispinae in the Old World are Arecaceae (Cocos, Metroxylon, 1% of the 159 genera described. Only six species of cassidines and numerous other palm genera), Pandanaceae (Pandanus have been reported as leaf-miners, accounting less than 1% of and Freycinettia), and Zingiberaceae. Numerous Leguminosae, the 2760 species in the Cassidinae. The reported geographical Asteraceae, Poaceae, and Verbenaceae have been reported as distribution and host plants are summarized for most of the host plants for the Hispinae in the New World. For larval over 500 species of suspected or documented leaf-mining Cryptostomes, 77% of the reported species feed on one plant chrysomelids (Table 1). Larval chrysomelids can be classified species. In adult Cryptostomes, 51% of the reported species Address for correspondence: Jorge A. Santiago-Blay, Department of Paleobiology, National Museum of Natural History, MRC- 121, Smithsonian Institution, 10th and Constitution Avenue, P.O. Box 370122, Washington, DC 20013-7012, USA. E-mail: [email protected] New Developments on the Biology of Chrysomelidae edited by P. Jolivet, J.A. Santiago-Blay and M. Schmitt © 2004 SPB Academic Publishing bv, The Hague, The Netherlands 2 J.A. Santiago-Blay only feed on one plant species. Leaf-mining chrysomelids are Sagrinae larvae are borers into semi-rigid stems and, uni- or bivoltine, particularly in temperate zones, but they can when the larva pupates, it makes a cocoon within be trivoltine or multivoltine in the tropics. Natural biological the stem gall. Currently, only sagrine larvae of the enemies of the immature stages of leaf-mining chrysomelids are abundant but, in most cases, these organisms seem to be Old World genus Sagra and the New World genus unable to control outbreaks of leaf-mining chrysomelids. Leaf- Atalasis are known to make galls. However, except mining appears to have arisen independently multiple times in for anecdotal observations, nothing is known about the Chrysomelidae, typically from most recent common an- the larvae of Megamerus and other Gondwanian cestors which were exophytic. Leaf-mining mostly occurs in sagrines. Most of them are probably gallicolous, but the Hispinae, and it may have evolved from ancestors living there are likely to be exceptions in Australia. Me- between closely appressed leaves of monocotyledons. Several gamerus, for instance, is said to be gallicolous in leaf-mining chrysomelids, especially hispines, are economi- cally important as pests of major crops; others are used as Madagascar (Jolivet to Santiago-Blay, personal com- biological control agents of weeds. munication, July 2003). A leaf-mining organism is one in which, mini- mally, one of its life stages actively tunnels or mines An introduction to leaf-mining insects the usually flattened expansions of shoots, the leaves. Leaves of vascular plants have three parts: base, pe- What is leaf-mining? tiole, and blade (or lamina). The largest and most often flattened portions of leaves are usually known Leaf-mining is the consumption of foliar material as the blades, although graminologists (students of contained within the epidermal layers, without elic- grasses, Poaceae) also refer to entire leaves as iting a major histological response from the plant. ‘blades’. Leaf-miners overwhelmingly consume the The study of leaf-mines is termed ‘minology’ (He- relatively softer tissue, or parenchyma, contained ring, 1951). Mines may have a thin rim of callus between the epidermal layers, although some leaf- tissue (Hering, 1951). Leaf-miners consume devel- miners tend to consume vascular tissues (Hering, opmentally differentiated tissue and their tunneling 1951). activities do not elicit a major proliferation of un- Leaf-mining is largely restricted to the larvae of differentiated tissue (Connor & Taverner, 1997). about a dozen families of the four major holometab- Superficially similar-looking structures on leaves, olous insect orders: Coleoptera (Buprestidae and known as pseudomines, are caused by a variety of Chrysomelidae), Lepidoptera (Nepticulidae, Gra- microorganisms, including fungi and viruses; feed- cillariidae (sensu lato), Incurvariidae, Tisheriidae, ing activities of non-leaf-mining insects; or as a Coleophoridae, Eriocraniidae, and Opostegidae), reaction of plants to margin-feeding (Hering, 1951). Diptera (Agromyzidae, Anthomyiidae, and Tephri- Mining leaves is one of several modes that in- tidae), and Hymenoptera (Tenthridinidae). In nu- vertebrates have of feeding and living inside plants merous species of insects, including leaf-mining (endophyty). Other endophytic ways of living may chrysomelids, the pupa and to a lesser extent the elicit a response from the plant in the form of exu- adult, also dwell within the mine. The larvae of leaf- date production (Langenheim, 2003; Santiago-Blay miners produce a relatively long-lived behavioral et al., 2002) and/or gall formation. Numerous in- record of their recent, as well as ancient herbivory, sects bore or otherwise penetrate the shoot (trunk, hence providing a unique window