3.6 Description of Trap Types
The most common passive, flight-intercept trap is the Malaise trap (Figure 1). The one used in this inventory is modeled after the description given by Townes (1962). For a complete review on Malaise traps see Steyskal (1981). Malaise traps work on the principle that many flying insects fly to the highest and brightest point (collecting head) when they encounter an obstacle (trap panels). This is a particularly effective method for collecting Diptera and Hymenoptera. A liquid-filled trough or pitfall should be placed along the base of the central wall to collect species that drop when they hit a barrier (e.g., many Coleoptera).
Figure 1. Design and construction of a Malaise trap. (From Martin 1977).
Length (center wall) 1.4 m; height (collection head) 1.8 m; volume of collection jar 1.75 L (Winchester 1992).
Pan traps are simple collecting vessels (e.g., plastic trays), filled with liquid (e.g., brine solution) that are placed flush with the ground. They mainly serve to capture ground-dwelling and low flying arthropods, including Arachnida, Coleoptera, and Orthoptera. A window trap incorporated above the pan trap enables collection of low flying arthropods, such as Coleoptera, that drop when they encounter an object. A cover should be placed above the window to protect the catch from rain. The pan can be painted yellow to attract several taxa. The details of this trap combination are shown in Figure. 2.
Figure 2. Design and construction of a standard window trap. (From Martin 1977).
Trap width and length should match pan trap specifications (e.g., minimum pan trap size: 23 x 23 cm).
Pitfall traps are containers (e.g., jars, plastic bottles, tins) that are buried so that the rim of the collecting container is flush with the surface of the ground. They mainly serve to capture ground-dwelling arthropods (similar to pan traps). A cover should be placed about two cm above the ground directly over the trap to exclude the rain, and a one inch (25 mm) mesh (e.g., hexmesh) screen placed flush with the opening to exclude small mammals and amphibians. The details of the trap are shown in Figure 3. Multiple pitfall traps can be used and connected by "drift fences". Aluminum flashing up to 30 cm high can be used to connect pitfalls. The details of this trap combination are shown in Figure. 4.
Figure 3. Design of a standard pitfall trap (from Martin 1977).
Trap volume should be 450 ml, and the diameter of opening a minimum of 8 cm.
Figure 4. Multiple pitfall traps.
Substrate cores are used principally to sample for soil arthropods. A simple bulb planter can be used to collect samples to a depth of five cm. The samples should then be run through an extraction funnel (Figure 5). Arthropods avoid the heat source (light bulb), and are driven down a funnel into a collecting vessel containing a preservative.
Berlese funnels can also be used to extract arthropods from litter or moss samples. Surface litter should be collected and first sieved to sort out large and mobile arthropods (e.g., arachnids, beetles). Contents are then placed into a garbage bag for transport to lab and then run through a Berlese funnel. Very small arthropods can be extracted using a technique described by Besuchet et al. (1987).
Figure 5. A single Berlese funnel (from Martin 1977).
Diameter of funnel should be at least 30 - 38 cm. A series of 12 funnels can be used simultaneously in a ventilated funnel box (Winchester 1992).
Terrestrial light traps are effective for trapping night-active insects, primarily Lepidoptera. Typically, mercury-vapor lamps (Figure 6) are used. However, black-light or other lamp sources high in ultraviolet emissions can be used, even white light (e.g., Coleman lantern) produces good results. There are portable light sources, with battery packs or generators, that enable light traps to be run when an electrical source is unavailable (see Gerber et al. 1992).
Two principal methods of collecting samples from light traps in the field exist. They are: (a) a white sheet placed on the ground or suspended in front of the light source (any insects that are attracted to the light are then manually collected from the sheets), and (b) a simple funnel trap placed below the light source. Insects attracted to the light strike the funnel or baffles and fall into the bottom of the trap where they can be manually removed and processed.
Figure 6. A mercury vapour trap (from Martin 1977).
(a) 125 W 200-220 V Osram mercury-vapour globe, (b) four metal baffles, (c) metal funnel, (d) metal inner killing chamber, (e) rain drain with tube leading to the outside of the trap.