Conservation of Biological Diversity: A Key to the Restoration of the Chesapeake Bay Ecosystem and Beyond. G. D. Theires, editor. Maryland Department of Natural Resources, Annapolis, MD, 1998 THE LEAF BEETLES (INSECTA: COLEOPTERA: CHRYSOMELIDAE): POTENTIAL INDICATOR SPECIES ASSEMBLAGES FOR NATURAL AREA MONITORING C. L. Staines and S. L. Staines 3302 Decker Place, Edgewater, MD 21037 Abstract: Chrysomelids are model herbivores. Most species are monophagous or narrowly oligo- phagous on a small number of plant families. In the tropics, the area most studied, chrysomelids have been found to be an excellent indicator of local species richness, due to not only their relative abundance but the ease of morphospecies sorting by a nonspecialist. The diversity of chrysomelids is exceptionally rich and a function of local plant diversity. These factors make chrysomelids an excellent candidate for indicator species assemblages for natural area monitoring. A project was started in 1997 on Plummers Island, Maryland, to determine whether chrysomelid species assemblages are indicators of plant diversity, site disturbance, and environmental heterogeneity. At this site we have the advantage of historical collection data dating back to 1901 that can be used as baseline information. : - ' , • INTRODUCTION .. the major shapers of ecosystems. Many think that Arthropods represent approximately 90% of all ecosystems such as the African savannah are shaped by species including plants (Pimentel et al. 1992), with vertebrates, but without the coprophagous arthropods the insects accounting for approximately 80% of all animal system would soo'n be overwhelmed with accumulated species diversity (Samways 1992). Together with micro- dung. Our dependence on invertebrates for survival is organisms, insects make up most animal biomass and mostly ignored (Wilson 1987). show the greatest diversity of ecological roles (Coulson Arthropods are found in every conceivable habitat and Crossley 1987). They are also known to be especial- and have many different functions important in ly vulnerable to small-scale habitat destruction (Ehrlich sustaining the balance of ecosystem processes (Wilson and Murphy 1987; Murphy et al. 1990). 1987; Hawkins and MacMahona1989; Walker 1992). American culture views arthropods as pests that need Insects are highly specialized in their niche require- to be controlled or eradicated (Byrne et al. 1984; ments, with diverse ecological roles that provide Howarth and Ramsay 1991; Kim 1993). The public's low important services to the ecosystem processes, as decom- esteem of invertebrates and fear of "creepy crawlies" is posers, consumers, predators, and parasites (Swift and exploited by the advertising industry's message that the Anderson 1989; Morris et al. 1991; Miller 1993). The only good bug is a dead bug. The only exceptions are active decomposition of plant and animal matters by aesthetically accepted species (e.g., butterflies) and those flies, termites, and beetles is essential to material- perceived as economically beneficial (e.g., honey bees). recycling systems (Frost 1959). Predators play an This negative perception and disproportionate amount of important role in regulating populations of phytophagous attention extends to conservationists (Pyle 1976; Mc- pests (DeBach and Rosen 1991; Olembo 1991). Arthro- Naughton 1989; Hafernik 1992). pods and other invertebrates are the major movers and It is a common misconception that vertebrates are shakers in subterranean ecosystems including litter 233 layers. They are involved in every aspect of the eco- feeding, and mating may all occur on one or a few neigh- system processes (Kiihnelt 1976; Paoletti et al. 1991). boring plants. Even in infertile or impoverished habitats, arthropods support the ecosystem in which insectivorous vertebrates INDICATOR SPECIES ASSEMBLAGES flourish (Braithwaite et al. 1988; Braithwaite 1991). The value of invertebrates as environmental indi- Within insects, beetles (Coleoptera) is the largest cators is only beginning to be appreciated (Magurran order, with more than 290,000 described species (Wilson 1988; Pearson and Cassola 1992; Oliver and Beattie 1987). Beetles are divided into 134 families, 114 of 1993). Indicator species are used to assess environ- which occur in America north of Mexico, they are found mental effects of human activities, determine regional living in just about every habitat except the open ocean, patterns of biodiversity, measure changes in community and they may occupy any trophic level (Downie and structure and function, and estimate land value (Hutto et Arnett 1996). al. 1987; Murphy et al. 1990; Noss 1990; Pearson and Chrysomelidae (leaf beetles) is one of the largest Cassola 1992). Insects show great potential as environ- families of beetles with approximately 50,000 described mental indicators because they are often specialized, they species worldwide placed in 19 subfamilies (Lopatin are easily observed and monitored in the field, and their 1977). This makes the family second only to the needs are often correlated with the needs of other fauna Curculionidae (weevils, Insecta: Coleoptera), and it has and flora (Wilson and Peter 1988; Samways 1989). more than twice the species richness of birds and Much of the previous work involving indicators has mammals combined (Klausnitzer 1981). In North used one or a few species. The weakness of this America, there are 1,481 species in 188 genera (Arnett approach is its narrow focus, which may result in the 1985). The chrysomelid fauna of Maryland has not been protection of one organism at the expense of others documented. Cavey and Staines (unpublished data) list (Landres et al. 1988; Kreman 1992, 1994; Kreman et al. 373 chrysomelid species in Maryland. 1993). Recently the concept of inventorying taxonomic Most chrysomelids live on terrestrial, aquatic, or assemblages that are likely to represent environmental subaquatic plant material as both larvae and adults as patterns, distributional patterns of species in other root, leaf, flower, or pollen feeders, whereas stem boring, unrelated assemblages, or the overall biodiversity of an leaf-mining, detritus-feeding, and ant-nest associates are area has been proposed (Kreman 1992,1994; Kreman et found among relatively few species. al. 1993; Pearson 1994; Favila and Halffter 1997). Chrysomelids are usually thought of as plant pests, A good indicator species assemblage should have both through direct plant feeding and through trans- several characteristics of which the most important are as mission of plant viruses (Selman 1988). Metcalf (1986) follows: (1) The indicator assemblage should be from a reported that the genus Diabrotica costs U.S. farmers $1 speciose taxon. The taxon should be important in the billion annually in corn alone. However, other chrysom- structure and function of the target ecosystem. (2) There elids perform useful roles in biological control of weeds must be sufficient information available on the taxonomy (White 1996), with the number of those being evaluated and natural history of the indicator assemblage to allow for such services increasing throughout the world. for the identification of species and the ecological Chrysomelids are also the target of biochemical pros- interpretation of the results. (3) The higher taxa should pecting. Many species sequester or modify plant be broadly distributed geographically and occupy a chemicals whereas others apparently manufacture a breadth of habitats. (4) The indicator assemblage must unique chemistry against predators (Pasteels et al. 1988, be easy to capture and the capture method must be 1994). Some of these compounds may be useful to standardized. An asymptote should be reached in several humans. weeks or months. (5) The indicator assemblage must be The Chrysomelidae are model herbivores. The one for which collection and other necessary activities majority of species are monophagous or narrowly can be carried out without jeopardizing the conservation oligophagous on a small number of plant families. of any member of the assemblage. (6) Capture data must Association with the host plant is intimate and pro- provide enough information to determine the com- longed. Oviposition, larval feeding, pupation, adult position and structure of the assemblage and its inter- 234 action with the rest of the community. Chrysomelids with ant nests and feed on ant eggs, exuviae, dead ant have not yet been evaluated as an indicator species bodies, and other refuse. Adults feed indiscriminately on assemblage but with a properly designed protocol the flowers, buds, young leaves, and pollen. Females either family meets all of these characteristics. drop their eggs to the ground or glue them to leaves. Eggs resemble seeds and are carried by ants to their Speciose Taxon nests. Not all clytrine larvae live in ant nests, but larvae There are approximately 50,000 chrysomelid species of species in some genera live under stones in the vicinity worldwide (Lopatin 1977), making the family the second of ant nests (Jolivet and Hawkeswood 1995). largest in the animal kingdom. It has more than twice Cryptocephalinae - Larvae of the 2,300 described the species richness of birds and mammals combined worldwide Cryptocephalinae species are free-living case (Klausnitzerl981). bearers and are either phytophagous or detriticolus. Adults are phytophagous on a wide range of plant Natural History families (Jolivet and Hawkeswood 1995). As with most large groups, the Chrysomelidae is Chlamisinae - The larvae of this