Efficacy of Electrocuting Devices to Catch Tsetse Flies (Glossinidae) and Other Diptera.
BACKGROUND
The behaviour of insect vectors has an important bearing on the epidemiology of the diseases they transmit, and on the opportunities for vector control. Two sorts of electrocuting device have been particularly useful for studying the behaviour of tsetse flies (Glossina spp), the vectors of the trypanosomes that cause sleeping sickness in humans and nagana in livestock. Such devices consist of grids on netting (E-net) to catch tsetse in flight, or on cloth (E-cloth) to catch alighting flies. Catches are most meaningful when the devices catch as many as possible of the flies potentially available to them, and when the proportion caught is known. There have been conflicting indications for the catching efficiency, depending on whether the assessments were made by the naked eye or assisted by video recordings.


RESULTS
Using grids of 0.5m2 in Zimbabwe, we developed catch methods of studying the efficiency of E-nets and E-cloth for tsetse, using improved transformers to supply the grids with electrical pulses of ~40kV. At energies per pulse of 35-215mJ, the efficiency was enhanced by reducing the pulse interval from 3200 to 1ms. Efficiency was low at 35mJ per pulse, but there seemed no benefit of increasing the energy beyond 70mJ. Catches at E-nets declined when the fine netting normally used became either coarser or much finer, and increased when the grid frame was moved from 2.5cm to 27.5cm from the grid. Data for muscoids and tabanids were roughly comparable to those for tsetse.


CONCLUSIONS
The catch method of studying efficiency is useful for supplementing and extending video methods. Specifications are suggested for E-nets and E-cloth that are ~95% efficient and suitable for estimating the absolute numbers of available flies. Grids that are less efficient, but more economical, are recommended for studies of relative numbers available to various baits.
South African Centre for Epidemiological Modelling and Analysis, University of Stellenbosch, Stellenbosch, South Africa; Natural Resources Institute, University of Greenwich, Chatham, United Kingdom.
Glyn A
GA
Vale
South African Centre for Epidemiological Modelling and Analysis, University of Stellenbosch, Stellenbosch, South Africa.
John W
JW
Hargrove
Early Warning Systems, Wembley, Pietermaritzburg, Kwazulu-Natal, South Africa.
N Alan
NA
Cullis
Division of Tsetse Control, Harare, Zimbabwe.
Andrew
A
Chamisa
Liverpool School of Tropical Medicine, Liverpool, United Kingdom; Warwick Medical School, University of Warwick, Coventry, United Kingdom.
Stephen J
SJ
Torr
D000818:Animals; D001522:Behavior, Animal; D055615:Electrical Equipment and Supplies; D004772:Entomology / Q000295:instrumentation* / Q000379:methods*; D007303:Insect Vectors; D014370:Tsetse Flies / Q000502:physiology*