As we increase our understanding of insect responses to environmental factors, insects become useful indicators of changing conditions (Dufrêne and Legendre 1997). Because of their sensitivity to climate or biochemical changes in their resources and rapid reproductive rates, insects may provide early warning of changes not yet apparent in the condition or abundance of plants or vertebrates, usually favored as bioindicators.
Insects have proved to be useful indicators of changing water quality (Hawkins et al. 2000). Chironomid midges have proved to be particularly useful indicators of water quality in aquatic ecosystems. For example, replacement of chironomid species characterizing oligomesotrophic conditions by species characterizing eutrophic conditions provided early indication of pollution in Lake Balaton, Hungary (Dévai and Moldován 1983, Ponyi et al. 1983).
Ant associations are used as indicators of ecosystem integrity and the status of restoration efforts in Australia (A. Andersen and Majer 2004). Similarly, grasshopper (see Fig. 5.7), dung beetle (see Fig. 9.6), and ground beetle assemblages can be used to assess ecosystem integrity and recovery status (Fielding and Brusven 1995, Klein 1989, Niemela and Spence 1994, Niemela et al. 1992). Because of their sensitivity to host defenses, insect herbivores could be used as indicators of change in plant biochemistry before visible chlorosis or other symptoms of stress become apparent.
The sequence of insect species occurrence during heterotrophic succession in decomposing carcasses has been applied by law enforcement agencies. Het-erotrophic succession in carrion (see Figs. 10.3 and 10.4) provides the foundation for determining time of death under various environmental conditions (Byrd and Castner 2001, Goff 2000, K. Smith 1986, E. Watson and Carlton 2003). For example, the rate of fly colonization of a corpse differs between exposed or protected locations. Research on the sequence and timing of colonization by various insect species on corpses under different environmental conditions has contributed to establishing time of death and opportunity by suspected perpetrators. This has enhanced the ability of law enforcement officials to convict murderers and wildlife poachers.
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