*2.1.2 On the basis of origin of organism*

It is classified as active and passive bioindicators.

**Active bioindicators:** A type of bioindicators that are exposed at particular place for specific time interval thus used to examine the concentration of compounds and elements are called as active bioindicators.

**Figure 3.** *Characteristics of insect as bioindicator.*

**Figure 4.**

*Transfer of heavy metals to insects through contaminated soil.*

*Recent Advances in Evaluating Insects as Bioindicators of Heavy Metal Pollution DOI: http://dx.doi.org/10.5772/intechopen.110212*

**Passive bioindicators:** A type of bioindicators collected from their natural ecological community used to analyze the concentration of compounds and elements and their direct and indirect effect are called as passive bioindicators.

### **2.2 Insect as bioindicator**

Insect is utilized as an efficient bioindicator of heavy metal pollution because of their diverse richness of species, easy handling and traps are good enough for effective statistical analysis. They are generally collected for their role as predator and significant for biological control such as spider and beetles (**Figure 3**). Heavy metals have negative influence on insect impacting their fecundity, weight, mortality and developmental stages [22, 23]. Furthermore, insects enable the selection of behavioral and demographic factor with strong association to the predefined abiotic factor that can be observed and quantified in particular environment [24]. Insects can be impacted directly by various means as associated with polluted soil and air deposition (**Figure 4**). Parasites and predator are also affected if they consume the insect that have greater amount of the heavy metals [25].

### **3. Bioaccumulation in insects**

Metals are non-degradable as compared to other contaminant elements thus show bioaccumulation in the trophic chain [26] as **Figure 4** displaying bioaccumulation of heavy metals in insects. Insects are potent source of bioindicators to determine the toxicity of heavy metals and human activities in terrestrial ecosystem as they are closely associated with the sediments [27].

Bioaccumulation of the pollutant is also influenced with the feeding behavior of insects as herbivorous and omnivorous usually have lower heavy metal concentration than predatory and carnivorous insects [28]. Corbi *et al*. [29] had emphasized the

**Figure 5.** *Schematic presentation of bioaccumulation of heavy metals via food chain.*

contamination of aquatic ecosystem [29] as a consequence of utilization of different heavy metal accumulation including lead, cadmium, chromium, zinc, nickel [30] as fertilizers for agricultural practices that had major impact on the water supply of surrounding cultivated areas. Meanwhile, the lack of riparian vegetation is another major cause of bioaccumulation of toxic metals from the surrounding cultivation [30, 31]. Owing to the significance and placement in food chain, heavy metal accumulations are detrimental to global health. Metal accumulation of aquatic invertebrates and sediment deposition provide a potential link to the upper trophic level of the food chain [32] as illustrated in **Figure 5**.
