Tropics

Collecting Systems for large catches

A large, durable plastic bag collector is best for very large catches of tsetse and biting flies at traps that remain unattended for several days or longer. I prefer to use an intermediate plastic bottle to avoid separation of the bag from the cone, but with care, the bag can also be placed directly over the exit from the cone (but tape or tie it down carefully).

Use strips of scrap netting or similar ties stapled to the corners of the bag to tie it to fabric loops sewn into the top front corners of the trap. Attach similar ties above to the suspension pole. Several ties with tension keep the bag stable in high winds.

An appropriate tie must be used to keep the hole in the bag securely fixed over the neck of the bottle. Use a bottle with a long neck, and keep the hole in the bag small. Slide the bag over the neck of the bottle and run the tie with good tension back to the suspension wires and / or the bottle. This connection is critical.

Large mesh bags may be more suitable for areas with very high winds or high humidity to keep specimens in reasonable shape for identification, but I have yet to test this option. In summer in Canada, the flies dry out reasonably well, but they do sometimes rot in the bag during humid weather. Plastic bags have mostly been used in hot and dry areas for tsetse traps in Africa, where rotting is not a problem.

When traps are left unattended for a very long time, the end of the bottle may need to be cut off and a small, mesh bag may need to be attached to collect flies that die while still inside the bottle. This will prevent the area of the exit hole from becoming clogged with dead flies. In Canada, this has not been a problem for very large catches of tabanids (1,000's) with traps checked on a weekly basis.

For similar "tried and true" systems, see the information at the
Natural Resources Institute, United Kingdom on Bait Technologies.
This is well-illustrated with step-by-step, practical examples.

For frequent changes of collectors (e.g. daily), I use long mesh sleeves rather than plastic bags to minimize problems with wind, and to avoid any effects on fly behaviour towards the trap (Collectors for the North). In bright sunlight, a large plastic bag at the top of the trap is a conspicuous object with considerable glare, especially in the ultraviolet (Traps in Nature).

Nails Supporting Bag 11k

When traps are left unattended for a month or more in a typical tsetse control operation, a central pole is often used. The system at left uses three nails spread apart at the top of a thick wooden pole. The nails support a metal washer sewn into the top of the cone.

Four nails supporting a plastic bottle top "funnel" is a much better option.

The problem with the "nails + washer" system is that the bag may shift relative to the exit hole, e.g. when tension is lost, or if animals interfere with the trap. The washer may also slip off the nails, blocking the exit hole. Finally, the netting may tear where the washer is sewn into the cone. Hence, use of a plastic bottle top is now recommended.

The central pole supporting the trap may also have an effect on the upward movement of flies, but this has not been investigated.

Animals often interfere with collectors when they attempt to eat dead flies accumulating in the bag. One simple deterrent is automotive grease containing large quantities of chili powder. This can be smeared on the base of the collecting bag. Birds can be also be troublesome, requiring substitution of aluminum screening for materials such as netting or plastic.

Making a Collecting Bag

Use a heavy gauge, clear plastic bag in a large rectangular format (60 x 40 cm). The instructions below are based on the bag used by Brightwell et al. (1987). I have been using this type of bag in Canada and it works well.

	Fold the bag almost in half, away from the open end, leaving a 2-cm hanging margin for closing later. Snip a very small hole in one corner while the bag is folded, this will form the entrance hole and should be small at the start; it can be stretched later.
	Lay the bag flat and pull up at the open end to separate the sides and give the bag a tetrahedral shape. Put two small round pebbles inside before you close (these add weight, reinforce the corners, and make it easier to add ties).
	Fold back the 2-cm edge at the opening towards the entrance hole (this lets water drain out when the bag is set up in the normal way). Staple the edge to seal it (use staples rather than a heat sealer so that the bag can be taken apart easily and washed). You should now have a closed tetrahedron.
	At the opposite corner on the side with the exit hole, punch in the plastic bag to fold it in about one third of the way. This will make a new indented corner and a flat bottom containing the entrance hole.
	Position the two pebbles, one in this new corner and one at the peak opposite the entrance hole. You now have a tetrahedron with a pinched corner that will lie flat against the cone of the trap.
	Use scrap mosquito netting or cloth to attach ties to the corners containing the pebbles. Attach two more ties to the bottom corners with a stapler. Attach a final tie next to the entrance hole. This last tie is critical; it is used to align and fix the bag to the trap exit hole.