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Insects as bioindicators

D. L. A. Underwood
Biology 316 - General Entomology

A. Definitions

1. Bioindication

a. Bioindication or biomonitoring can be considered a type of applied ecology.
b. Its primary goal is to use organisms living within natural communities to monitor the

impact of disturbance and to use this knowledge in the management of the ecological
system.

c. Bioindication can also be used in urban settings and in agricultural communities.
d. Biomonitoring has been around since 1908 when two workers in Germany published a

paper on using macroinvertebrates to assess water quality and degrees of pollution in
rivers subject to sewage contamination.

e. We didn't begin to use biomonitoring until the 1970's.

2. Indicator taxa

a. An indicator taxon is one that is of narrow amplitude with respect to one or more

environmental factors.

b. When the species is present, it indicates the presence of certain environmental

parameters. See attached table.

B. Levels of biomonitoring

1. Environmental indicators

a. A taxon that responds predictably, in ways that are readily observed and quantified, to

environmental disturbance or to a change in the environmental state is a good
candidate species for use in biomonitoring.

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b. Organisms are used as early-warning devices or to delimit the effects of a disturbance

(like an effluent).

c. Organisms can be used as accumulators of chemicals that are used to bioassay the

presence or concentration of pollutants.

d. Organisms are used to rank pollutants in order of toxicity.

2. Ecological indicators

a. Rather than merely functioning as gauges of environmental change, taxa are used to

demonstrate the effects of habitat alteration or fragmentation or climate change, etc.

b. Indicator taxa act as surrogates for the larger community.
c. The response may be a decline in population size, a change in spatial distribution, or any

number of life history changes.

d. This response is representative of the response of at least a subset of other taxa present in

the habitat.

3. Biodiversity indicators

a. A biodiversity indicator is a group of taxa (e.g. genus, tribe, family, or order) or

functional group, whose diversity reflects some measure of the diversity of other taxa
in a habitat.

b. These measures of diversity could include character richness, species richness, level of

endemism, genetic diversity, to name only a few.

c. The diversity measure of the indicator taxa can be used to estimate the diversity of other

taxa.

4. Scale of biomonitoring (see attached table once again)

a. Biochemical and physiological levels
a. Individual level
b. Population and species assemblage level
c. Community level
d. Ecosystem level

5. Team project - A takes notes, B speaks

a. Without looking ahead in the outline, come up with three practical reasons for using

living organisms as bioindicators.

C. Why bioindication?

1. Alternatives

a. Direct measurements can be made of physio-chemical factors of an environment.

i. In terrestrial systems, it is common to know the type and degree of

environmental change, for example, habitat fragmentation, species
introduction, etc.

• However, it can be difficult to monitor every potentially important aspect of a

system.

• The problem also arises as to whether we, as a scientific community, are aware

of all the important things to monitor.

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ii. In aquatic systems, the problem is much more complex than that seen in

terrestrial systems. Water quality requires

• knowledge of which of the hundreds substances to monitor,
• understanding the synergistic effects when two or more pollutants interact,
• and continuous monitoring to detect pollutants whose release may be

intermittent, such as nocturnal release of industrial waste products.

b. In general, we need to know what to measure before we can measure it.
c. Often these types of monitoring programs are expensive and extremely labor-intensive.
d. Synergistic effects will go unmeasured.
e. Our knowledge base is insufficient; we don't know enough about the natural world to be

able to reliably predict the impact of many disturbances.

2. Biological monitoring using insects has many advantages

a. Many taxa differ with regard to their sensitivity to environmental change and habitat

requirements so we can choose the taxon according to the needed resolution.

b. We can focus on functional groups such as primary consumers or top predators to

monitor ecosystem function.

c. There is a general lack of ethical constraints in sampling insects. No one really cares if

they are killed in the monitoring process.

d. Insect populations tend to be very large, so that killing a few hundred individuals will

not negatively impact the population.

e. Insects can be the "canaries" for environmental damage that can harm humans, such as

water quality or the build up of toxic chemicals.

f. Our primary goal for environmental monitoring is to ascertain the effects of the

disturbance on life. Using living creatures satisfies this goal in a direct manner.

D. Aquatic insects as bioindicators

1. Factors governing aquatic insect distribution

a. Oxygen availability
b. Temperature
c. Sediment and substrate type
d. Presence of pollutants such as pesticides, acidic materials and heavy metals

2. Typical responses to aquatic insect communities following disturbance

a. As particulate material including sediment increases, certain species of mayflies

(Caenidae) with protected abdominal gills, and caddisflies like the filter-feeding
Hydropsychidae increase in relative abundance.

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b. When dissolved oxygen is reduced, haemoglobin-possessing bloodworms

(Chironomidae) increase in number.

c. Stonefly nymphs decline as temperature increases.
d. Pesticide runoff leads to substantial reduction in species diversity.
e. If nutrient levels increase due to fertilizer run off or livestock yard wastes entering the

water, a few species will increase dramatically with concomitant general decline in
species diversity.

E. Terrestrial insect bioindication

1. Environmental indicators

a. Traditionally soil invertebrates were used to indicate soil fertility and pollutant levels.
b. Recently, bioindication is used in terrestrial systems for a variety of situations.

i. Direct measurement may be cost prohibitive.
ii. Environmental changes may be subtle and a result of complex interactions

between abiotic and biotic components that cannot be measured directly.

iii. Sometimes, the biotic community continues to change long after physical or

chemical traces of the impact are no longer measurable.

iv. Biomonitoring for quantifying the effects of environmental pollutants on cancer

risk is now preferred in many cases.

2. Ecological indicators

a. This aspect of bioindication is still in its infancy.
b. Most studies still focus rare and endangered species.

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c. Ideally, we also demonstrate that rare and

endangered species are representatives of
other taxa.

d. Few studies have progressed to this level.

i. Kremen (1992) tested the usefulness of

using butterfly species diversity as an
indicator for ecological parameters in
Madagascar.

ii. Butterflies typically are sensitive to

microclimate and light level changes
and they interact with specific host
plants as larvae and adults.

iii. He found that butterflies were

excellent indicators of heterogeneity
due to topographic or moisture
gradients, moderate indicators for
predicting floral richness, limited
indicators of heterogeneity due to
human disturbance, and poor
indicators of plant diversity.

3. Biodiversity indicators

a. Using indicators to estimate biodiversity is

faster and less expensive than conducting
comprehensive biodiversity surveys (if
such surveys were even possible).

4. Team project - B takes notes, C speaks

a. Identify five desirable qualities for indicator taxa of biodiversity.

5. Biodiversity indicators continues

a. While only a few taxa have been identified to date that may be efficient biodiversity

indicators, the science is rapidly expanding.
i. Tiger beetles may be particularly good for indicating regional patterns of

biodiversity because of their stable taxonomy, well-understood biology and
life history, ease of sampling, world-wide distribution, presence in a wide
range of habitat types and specialization of individual species within habitats.

ii. For similar reasons, scarabaeid beetles are also candidate taxa.

b. Brown (1991) identified 12 "desirable qualities" for indicator taxa and evaluated a

variety of insect groups in this light.
i. High scorers included Collembola, Formicidae, Ithomiinae butterflies, Isoptera,

and Coleoptera. (see last table attached to outline)

c. Current thoughts revolve around identifying several indicator taxa as work by

Prendergast (1997) and Lawton (1998) has questioned the efficiency of using single
taxon groups as measures of total biodiversity.
i. These are called "predictor sets" or "shopping baskets" of taxa.

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ii. The predictor sets would ideally encompass different ecological functional

groups. We might choose butterflies, termites, ants and dung beetles to
estimate diversity in a tropical forest.

• Butterflies are phytophagous.
• Termites and ants are numerically the most dominant macroinvertebrate taxa

in the soil and canopy, respectively.

• Termites and dung beetles are decomposers.

iii. The drawbacks to using predictor sets, of course, come down to money and time,

neither of which conservation efforts have.

d. The biggest problem is that in areas of highest risk, we know the least about their

invertebrate fauna.

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