PAN TRAPS

L. Masner

Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Ottawa, Ontario, Canada K1A 0C6

Introduction

Many insects are attracted to the colour yellow, especially bright sunflower yellow. Thus, yellow containers filled with water can be used to trap them. Detergent is added as a surfactant to break the surface tension of the water causing the insects to drown, and salt is added as a preservative.

Methods

Equipment consists of the pan traps - yellow watertight containers, water, pure detergent, salt, aquarium net, sample bags, alcohol, soft-lead pencil, quality label paper or card stock, twist ties, and a container for carrying water. Pan traps may be made from a variety of sources including yellow garbage bags, yellow vinyl sheets, transparent food trays spray-painted with acrylic yellow on the outside, aluminum roasting pans sprayed with yellow enamel on the inside, or recommended here are yellow plastic bowls (270 mm diameter x 78 mm depth). Depth of the trap can vary depending on regional aridity (deeper to contain more water in dryer regions or for longer servicing intervals) but the surface area (diameter) should remain constant. The water can either be from a tap or from natural sources, the latter should be filtered through the aquarium net to remove insects and mites. Detergent should be unscented so as not to act as an insect repellant. Self-sealing plastic bags (i.e. whirlpak type) are most convenient for field specimen storage. Alcohol is preferably 90% ethanol but 70% isopropyl will work and is available in most countries.

Traps should be placed in areas where people will not steal or vandalize them. Best sites to trap a diversity of insects have low ground vegetation (up to 50 cm), are moist and at least partly shaded. When using soft-bottomed traps remove stones and sharp objects that may pierce the traps. The most productive method for qualitative sampling is to set up a trap line of 5 to 100 traps along a transect through a variety of microhabitats in a particular area.

The pans should be sunk into the ground with their rims level to the surface. When time is short pans can sit on the surface but will not collect surface-active arthropods. Vinyl sheets can be made into rectangular trays by tying the corners with twist-ties and using a sharpened stick or metal skewer at each corner. Each corner is tied to the stick to prop up the trap. The stick should be inserted into the ground at about 45° to provide optimum support for the walls. For additional support of vinyl pan traps, sticks or rocks can be placed against the mid-point of each wall. The latter is necessary if the trap is not sunk in the ground as water in the trap will cause the sides to bulge outward.

Water, salt and detergent are then added to the trap. The traps are filled about 3/4 with water and enough salt to make a saturated solution. About 5 drops of detergent are added as a surfactant. If traps are to be emptied every 2 days or more frequently the no salt is needed but with longer servicing intervals (to a maximum of 7 days), salt is essential.

Traps are serviced by scooping out the contents with an aquarium net and then either reusing the old solution or replacing it with fresh water, salt and detergent. Before scooping remove large objects such as leaves, twigs, small animals, etc. that may have fallen into the trap. The net should be dragged gently near the bottom in one direction several times until the contents are recovered. Specimens can be processed for each trap or pooled depending on the objective of the sampling program. Check trap to see if it is still level, top up with water (if necessary), and add more salt and detergent at each servicing. Most importantly, ensure that the solution is transparent enough for the yellow background to show through.

Specimens are transferred to plastic bags from the net using a squeeze bottle of water to remove last specimens if each trap is to be processed separately (label in each bag), or place the net in the bag with specimens to prevent drying if sample is pooled. Specimens are processed the same day in a lab or base camp by rinsing the contents of each bag in the net under a gentle stream of water for several minutes to remove dirt, salt and detergent. Pick out any remaining large debris. Fresh water washing is essential because the detergent and dirt will form a film on the insects if they are placed directly in alcohol. This film is difficult or impossible to remove once specimens are in alcohol, thus rendering the specimens much less useful. Invert net contents into whirlpak and using a squeeze bottle filled with alcohol gently wash contents out of net and down sides of whirlpak to bottom. Cover sample in the whirlpak with alcohol to at least level of sample volume.

Sample labels must be placed inside the bag with the specimens. Labels should be printed in soft-lead pencil or India ink on a small piece of good quality paper or card stock. Poor quality paper will disintegrate or printing will slough off. Use the following format: Country: smaller political unit, locality (town, village, and distance from), exact GPS reference in latitude longitude, elevation, date or range of dates of collection (day, month in roman numerals, year), collector name, collecting method (pt - pan trap, mt - Malaise trap), habitat, accession code or field log number.

Example CANADA: Alberta
CFB Suffield
50°37.678'N 110°18.371'W
710m 1-VI-7-VI-1994
A.T. Finnamore pt
dune blowout 94.336

Store specimens in a cool dark place (refrigerate if possible), but not in direct sunlight or near a heat source. Replace alcohol with fresh 80% alcohol after 1 or 2 weeks. The sooner the catch is processed the better. For long-term storage (several months to years) it is essential to replace alcohol (to prevent freezing) and to keep the catch below freezing, preferably in a deep freeze at -10°C or lower to prevent specimen deterioration.

Material to be sent through the mail should be packed in hard protective containers such as mailing tubes or strong cardboard boxes. Bulk and weight can be greatly reduced by carefully draining out most of the alcohol from each whirlpak and replacing it with a small quantity of fresh 95% alcohol and washing the contents to the bottom of the whirlpak. Squeeze out air from the whirlpak and close by gently rolling down the end with twist-tie towards the other ens and clamping it. Removal of air and addition of only a little alcohol to the whirlpak is essential to prevent drying, sloshing and breakage of material during shipment.

The most frequent causes of damage to collected material are: 1) weak salt solution in traps; 2) drying out of material; 3) failure to rinse in fresh water before adding alcohol; and 4) failure to prevent sloshing of specimens during transportation.