Although insects have long been promoted as bioindicators, their value remains contested; this is well illustrated by the following viewpoints:
The wealth of existing, documented information on the relationship between invertebrates and habitat parameters, means that they offer great potential as indicators of biodiversity. In addition to being well-studied, invertebrates may be sampled using established, standardized methods, and expertise is widely available.
(Ferris and Humphrey, 1999) Insects and other microfauna … are of limited use in terrestrial systems because of the cost of sampling and processing and because there is limited acceptance by resource managers, politicians, and the general public.
(Niemi and McDonald, 2004) Andersen and Majer (2004) also recognize the constraints to widespread adop- tion of insects as bioindicators by land managers, because of the sampling effort and taxonomic expertise that is commonly required. However, given the demand for the development of bioindication systems, and the several distinct advantages and long history that insects have as bioindicators, their continued use in bioindication systems seems both essential and inevitable (Dobson, 2005). None the less, bioindication clearly extends beyond the use of insects, and valuable insights are to be gained by examining the development of the subject and the position of insects within it. Furthermore, insects are increasingly used along with other taxa, as well as non-taxonomic indicators
Monitor changes in biodiversity Biodiversity
Estimate diversity of taxa in a specified area Monitor longer-term stressor-induced
changes in biota Ecological
Demonstrate the impact of a stressor on biota
Monitor changes in environmental state Environmental
Detect change in environmental state Alternative functions
Indicator used to:
Indicator category
Fig. 7.1. The function of bioindicators in each category of bioindication. (Redrawn with permission from McGeoch, 1998.)
to achieve indication objectives (Watson, 2005), and thus should not be con- sidered divorced from developments in the broader field.
A summary of recent literature1 on bioindication demonstrates the domin- ance of environmental bioindication studies. Environmental bioindicators are generally at a more advanced stage of development than the other two cat- egories, particularly freshwater monitoring schemes involving macroinverte- brates, e.g. the River Invertebrate Prediction Classification System used in the UK to monitor the pollution status of water courses (Wright et al., 2000) and the South African Scoring System (SASS) (Chutter, 1972; Hodkinson, 2005;
Revenga et al., 2005). By comparison, the studies on biodiversity indicators remain surprisingly few (Fig. 7.2a). Insect (freshwater and terrestrial) pub- lications are dominated by ecological, followed by biodiversity indication, illustrating the relative importance of these categories in insect bioindica- tion (Fig. 7.2a). The volume of research in above-ground terrestrial environ- ments is fairly similar to that conducted in aquatic (marine and freshwater) envir onments, whereas there are comparatively few soil-based studies (based on the search-terms used here) (Fig. 7.2b). The latter is surprising consider- ing that bioindication systems for soils are comparatively well-established (van Straalen and Krivolutsky, 1996; van Straalen and Verhoef, 1997; Cortet et al., 1999; Viard et al., 2004; Parisi et al., 2005), but perhaps reflects the more advanced status of this field. With the obvious exclusion of the marine envir- onment, the distribution of insect studies across environments is similar to that for all studies, although there has been comparatively more work in above-ground terrestrial environments (Fig. 7.2b).
From a taxonomic perspective the literature is dominated by studies on plants (particularly lichens as pollution indicators) and invertebrates (includ- ing insects), together constituting over 65% of all publications (Fig. 7.3a).
Amongst Arthropoda, the hexapods encompass the vast majority of stud-
Environmental Ecological
Policy
Biodiversity General
Category 0
10 20 30 40 50 60 70 80
Percentage (%)
(a)
Terrestrial Freshwater
Marine Soil Environment
0 10 20 30 40 50 60 70
Percentage (%)
(b)
Fig. 7.2. Frequency of bioindicator publications: (a) on different forms of bioindication; and (b) conducted in different environments. Solid bars are for all bioindication publications (n = 2311 (a), 2088 (b) ), whereas hashed bars are for arthropod bioindication publications only (n = 283) (see Endnote).
ies (Fig. 7.3b), with the Coleoptera and Hymenoptera (Fig. 7.3c), and ants, ground beetles and bloodworms (chironomid larvae) (Fig. 7.3d), most fre- quently represented. The Coleoptera, especially ground, tiger and dung bee- tles, are certainly well recognized as ecological bioindicators and have also been tested in biodiversity assessments (Pearson and Cassola, 1992; Pearson and Carroll, 1998; van Jaarsveld et al., 1998). Dung beetles have been exten- sively used in studies as indicators of disturbance and habitat quality, partic- ularly in the tropics and subtropics (Spector and Forsyth, 1998; Van Rensburg et al., 1999; Davis et al., 2001, 2004; Halffter and Arellano, 2002; Avendano- Mendoza et al., 2005). Ground beetles have been applied in similar contexts, although studies are geographically skewed to higher latitudes (Kromp, 1999; Paoletti et al., 1999; Magura et al., 2000; Niemelä et al., 2000a; Cole et al.,
Plant Invertebrate* Arthropod Fish Abiotic Vertebrate* Bird Microbe Human
0 5 10 15 20 25 30 35
Percentage (%)
Hexapoda Arachnida
Crustacea Diplopoda
Chilopoda 0
50 100 150 200 250 300 350
Number
Coleoptera Hymenoptera Diptera Lepidoptera Araneae Collembola Acari Odonata Orthoptera Trichoptera Plecoptera Hemiptera Ephemeroptera Other 0
4 8 12 16 20 24
Percentage (%) Formicidae Carabidae Chironomidae Apidae Scarabaeidae Staphylinidae Cicindelidae Culicidae Coccinelidae Curculionidae Drosophilidae Simulidae Syrphidae Geometridae Other
0 2 4 6 8 10
Percentage (%)
(a)
(d) (c)
(b)
Fig. 7.3. Frequency of bioindication publications involving different taxa. (a) *Invertebrate category excludes terrestrial and freshwater arthropods and *vertebrate category excludes fi sh, birds and humans (n = 2061). The abiotic category includes studies that do not use species information as the indicator. Microbes include, for example, bacteria, protozoa and dinofl agellates. Publications including: (b) taxa in terrestrial and freshwater arthropod classes (n = 287); (c) arthropod orders (‘Other’ includes Isoptera, Dermaptera, Mantodea and Thysanoptera); and (d) insect families (n = 160, ‘Other’ includes Buprestidae, Cerambicidae, Chrysomelidae, Dytiscidae, Lucanidae, Tenebrionidae, Sarcophagidae, Braconidae,
Chalcidoidea and Chrysopidae).
2002; Allegro and Sciaky, 2003; Buchs, 2003a). The use of Hymenoptera in bioindication studies includes largely ants, but also honeybees (particularly as environmental indicators of pollutant levels in agroecosystems (Celli and Maccagnani, 2003) ) and other apidoid communities (Tscharntke et al., 1998;
Brown and Albrecht, 2001; Gayubo et al., 2005). Ants have been strongly promoted as bioindicators, mostly of land use and restoration, because of their high diversity and functional importance, especially in the southern hemisphere (Brown, 1991; Andersen, 1997; King et al., 1998; de Bruyn, 1999;
Osborn et al., 1999; Alonso, 2000; Armbrecht and Ulloa-Chacon, 2003; Matlock and de la Cruz, 2003; Andersen et al., 2004; Parr et al., 2004; van Hamburg et al., 2004; Netshilaphala et al., 2005). Ants are also amongst the insect eco- logical bioindicators most extensively adopted by land managers (Kaspari and Majer, 2000; Andersen et al., 2002; Andersen and Majer, 2004) (see also Table 4 in Buchs, 2003a). A fairly novel application with apparent potential for future development is the use of invasive insect taxa, often Hymenoptera, in bioindication and monitoring (Kevan, 1999; Chapman and Bourke, 2001;
Cook, 2003; Revenga et al., 2005). Blood worms are commonly used as both environmental indicators of freshwater pollution (Pinder and Morley, 1995;
Hamalainen, 1999; Orendt, 1999; Meregalli et al., 2000; de Bisthoven et al., 2005) and of habitat quality (Brodersen and Lindegaard, 1999; Milakovic et al., 2001; Brodersen and Anderson, 2002).
The frequency of taxa in bioindication studies is, however, little different to the relative number of described species in each group, at least at the order level (Fig. 7.4). A clear exception is the Hemiptera that is under-represented in
Araneae Acari Collembola Ephemeroptera Odonata Phasmatodea Orthoptera Dermaptera Plecoptera Blattodea Mantodea Isoptera Psocoptera Phthiraptera Thysanoptera Hemiptera Coleoptera Siphonaptera Diptera Hymenoptera Trichoptera Lepidoptera
0 4 8 12 16 20 24
Percentage (%)
*
(
*
= 35.67)*
*
* *
*
*
*
*
* *
* *
* *
* *
* * * *
Fig. 7.4. The percentage of studies in which taxa appear in the literature (bars) compared with the percentage of described species in the same taxon (*). Described species percentages calculated from data in Gaston (1991) and Grimaldi and Engel (2005).
bioindicator studies. Although Auchenorrhyncha communities are considered good potential bioindicators (Duelli and Obrist, 2003; Nickel and Hildebrandt, 2003), the level of taxonomic knowledge of the group proves an obstacle to its use in many instances (Buchs, 2003a). By contrast, the spiders, mites and springtails are comparatively over-represented for their taxonomic diversity (Fig. 7.4). Mites and springtails are mostly used in agricultural and soil envi- ronments as indicators of habitat quality and contamination (Behan-Pelletier, 1999; Alvarez et al., 2001; Zaitsev and van Straalen, 2001; Ponge et al., 2003;
Geissen and Kampichler, 2004; Sousa et al., 2004), as are spiders (Gravesen, 2000; Wheater et al., 2000; Horvath et al., 2001; Gibb and Hochuli, 2002;
Woinarski et al., 2002; Cardoso et al., 2004a). Reasons for the frequency distri- bution of studies across taxa (Fig. 7.4) generally include the proportional spe- cies richness of the groups, but also the selection of taxonomically manageable or better-known groups, and taxa that are conspicuous, abundant and readily sampled or quantified (Brown, 1991; Buchs, 2003a).