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 are more suitable for areas with very high winds or high humidity to keep specimens in reasonable shape. In 2009 I tested the use of this style of mesh bag collector with good results. The bags were made out of robust grey fibreglass window screening, which was easy to sew.

Traps were left unattended for the month of July at my home in Ontario. I placed a small block of dichlorovos insecticide inside the bag (the yellow square in the photograph) to prevent maggots from developing in any decaying material. I also tested this type of bag without insecticide elsewhere for a 2-week interval. In both cases, the flies dried out even in very wet weather, and were mostly identifiable to genus, and sometimes to species. An alternative configuration could easily be set up with an alcohol bottle, if accurate identification of the species was desired.

With the addition of a velcro pocket for ease of access to the catch, this system appears practical for the kinds of very high daily catches that are possible in some areas, or for very long intervals between trap checks. The only potential problem is accumulation of dead flies in the bottle with some blockage of the funnel.

For other "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). You can also sew the same bag out of any mesh fabric; PVC-coated fibreglass window screening is best. The instructions below are based on the bag used by Brightwell et al. (1987). I have used this type of bag in Canada in both plastic and mesh forms for very high catches for collections at weekly or longer intervals, without problems.

	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.