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Invertebrates - Terrestrial and Aquatic |
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For ease of use, this summary of invertebrate sampling techniques is divided into two major groups: There two major groups of terrestrial insects: This requires different methods of sampling: for flighted insects - flight interception traps Flight
interception traps Impaction or sticky traps Description: range of substrates (e.g. plates, dishes) coated in long-lasting glue. Efficacy of the traps can be increased by use of different colours, depending on target species. Traps are heavily affected by weather conditions and effectiveness decreases as surface becomes clogged with dust and insects. Insects are removed from trap using solvents. back to flight interception traps Light
trap Description: the basic light trap comprises an electric bulb, a white sheet as a reflective surface and a funnel to collect insects close to the light source. Many traps use ultra-violet globes as they attract a wider variety of insects. Weather conditions (temperature, windspeed and rain) have a major affect on trap catches. back to flight interception traps Malaise
traps Description: a netting tent with one open side into which a small container is placed at the highest point. Insects flying or crawling through the opening move up the netting and are collected in the container. May be left for a number of days without checking. back to flight interception traps Pheromone
traps Description: based on the principle that sex pheromones of female insects can attract males over large distances. Typically a glass jar open at both ends with a sticky trap attached to the middle. A vial of insect pheromone is placed next to the sticky trap, which soaks up the pheromone and slowly releases it to the air. back to flight interception traps Suction traps Description: fixed or mobile engine-driven device that sucks insects into a fine mesh, which can then be collected in a container. back to flight interception traps Water
traps Description: simple method based on a yellow pan (colour attracts insects) with vertical baffles placed above the ground. Detergent may be added to water to decrease surface tension of the water. Insects are attracted to container and simply drown in the water. These include
Direct inspection Description: similar to active searches. A regular inspection of a specified area will enable sampling of a proportion of the obvious species present. Prior knowledge of invertebrate fauna is essential to be able to visually recognise species. There is a strong bias against cryptic species with this method. back to ground and vegetation traps Knockdown
sampling Description: an irritant spray such as natural pyrethrin is applied using an engine-driven or knapsack mistblower high into the tree. A ground sheet or collecting basket is placed below the canopy to collected dead invertebrates. back to ground and vegetation traps Pitfall
traps Description: consists of small metal, plastic or glass container sunk into the ground such that the rim is level with the soil surface. Mobile invertebrates fall into the trap and cannot escape. Trap can be filled with preservatives (usually mixture of ethanol and glycerine) or baits if intended to target certain groups. Trap diameter can vary with target group (small traps exclude larger invertebrates). Drift fences may be used to assist in sampling. Pitfall traps not suitable in wet conditions. back to ground and vegetation traps Shaking
and beating Description: a sheet or plastic cloth is laid out under the plant which is then shaken and beaten (don't be too cruel) and the dislodged invertebrates are collected quickly before they can escape. back to ground and vegetation traps Soil
and litter samples Description: a soil or litter sample from a set area or volume is collected and sieved to sample invertebrates. Water or heat may be applied to samples to stimulate activity. back to ground and vegetation traps Sweep
nets Description: an inexpensive and commonly used means of sampling invertebrates from vegetation. The net is swung a set number of times through ground vegetation (grass and shrubs), while pacing. To prevent invertebrates escaping the mouth of the net must be closed as soon as sweeping is completed.
For aquatic invertebrates there are a range of sampling techniques
available. You will already have encountered some information about
these if you have studied or are studying SBI
506. Dip-nets
Description: a mesh strip attached to a rectangular or triangular frame (with or without a handle). In running water, the net is placed on the stream bed and the substratum directly upstream is disturbed, causing organisms to flow into the net. In areas of low water flow, the dip-net is swept through the water (preferably through vegetation). This method is less quantitative then the Surber sampler, as it does not relate invertebrate density to an unit area of substrate. Surber
samplers Description: a rectangular quadrat to delineate sample area and a net into which the disturbed invertebrates are collected. This method is used in flowing water to assist in collecting. Grab
samplers Description: a portion of the substrate is removed using a range of implements. Most efficient when substrate particle size is less than 15 mm (pebbles). The total sample is placed in a container and invertebrates are sorted and identified back in the lab. Suction
samplers Description: similar to grab samplers in that a fixed portion of the substrate is removed by a suction device (usually hand driven). The total sample is placed in a container and invertebrates are sorted and identified back in the lab. Colonisation
samplers Description: an artificial substrate is provided for invertebrates to colonise. This method allows a quantitative measure of abundance per unit area of substrate.
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