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BIOLOGICAL TECHNIQUES

INSECT COLLECTION TECHNIQUES

1. Sweep net sampling

Collections of flying insects, or those inhabiting foliage, can be made using a sweep net. Several types of nets are available, with standard sizes being either 30.5 cm (12 in) or 38 cm (15 in) diameter. Aerial nets (net on the right) have an open mesh collection bag and are used mainly to capture flying insects, although they can be swept through light vegetation such as tall grass. Beating nets (net on the left) are made from canvas and are used to sweep through vegetation that could snag and tear a mesh bag. A sweep is a single back and forth sweep covering a 150⁰ to 180⁰ arc. Collected insects can be identified and counted live in the net, or placed in a container with a piece of paper towel soaked with non-acetone nail polish remover to kill them to facilitate counting.

 

2. Leaf litter sampling

Insects that inhabit leaf litter or mulch can be surveyed by placing some of this material in an apparatus know as a Berlese-Tullgren funnel, which is designed to separate insects from the litter. A simple funnel can be constructed by removing the bottom from a potable water bottle and placing a piece of 0.6 mm (1/4 in) mesh hardware cloth inside the neck of the bottle. The inverted bottle should be  supported over a container to collect the insects that come out of the litter. To facilitate the movement of insects from the litter, a 15W to 25W bulb placed over the funnel will cause the insects to move deeper into the litter, through the screen, and into the container. The preservative in the container can be 75 to 80% ethanol.

3. Light trap sampling

Although insects have good color vision, they do not see the same wavelengths of light as humans. The human eye can typically distinguish colors ranging from red (760 nm [nanometers]) to purple (380 nm), while it has been shown that most insects see colors from yellow / green (550 nm) to ultraviolet [UV] (340 nm). Since many nocturnal insects are attracted to UV, trapping or killing devices have been developed that use UV bulbs to attract insects either to a collection container (we call these light traps) or to an electric grid (we call these bug zappers). Because insects do not perceive light in the red to yellow range, we use yellow bug lights outdoors to reduce the number of insects attracted to areas around our homes. Since most humans see relatively well under yellow light, these bulbs allow us to see while not attracting many insects. A simple light trap design is illustrated below. It’s construction is also described. Traps can be built either as single units or as a series of lights that can be used to allow comparison among bulbs of different colors, from several manufacturers, or having different wattage.

 

4. Pitfall trapping.

Pitfall traps are collect populations of insects and other arthropods living on the ground surface. Typically, traps are set up and allowed to collect insects for a minimum of 24 hours. The basic trap consists of a container set into the ground so that the upper rim is flush with the ground surface. Since many insects are predators and will eat other insects in the trap, a solution to kill and preserve insects entering the trap is used.

5. Aquatic insect collections using D-framed nets

These nets have a opening with a flat side (the D part) (at left). They can be used like a kick-net, with the flat side placed on the stream bottom so that it collects organisms dislodged when submerged objects upstream are disturbed. It also can be used more like a dip net and scraped along submerged objects to dislodge and collect organisms, or the flat side can be pulled across the bottom sediments of a pond or stream to sample organisms in that habitat.

 

Note: This post is still undergoing developments. Please update constantly.