Abstract:
Field experiments, with 125 watt Mercury-Vapour light-traps, are described in
this Thesis. Catches of moths in water traps arranged in a circular mosaic
pattern around the light-trap were distributed bivariate normal. Comparisons
between the bivariate mean moth vector and the mean wind vector suggested
that the wind vector determined the distribution of moths around the light-trap.
In light winds, less than 1 metre/second, moths were randomly distributed
around the trap. In stronger winds the direction of moth displacement from the
trap was associated with the direction component of the mean wind velocity.
A second experiment with light and water traps was used to estimate the
effective light-trap radius. Two light-traps, surrounded by water traps, were
separated by up to 25 metres on different evenings. When one light-trap was
downwind of another the catch was significantly greater in the downwind trap.
However, in crosswind conditions the two catches were similar. Bivariate
methods were used to estimate that the effective trap radius was between 10
and 25 metres.
A further experiment, using multivariate correlation and regression analysis,
found that air temperature, windspeed and moonlight affected light-trap
catches. An algorithm is described to enable the calculation of moonlight
illuminance. Increased windspeed and increased moonlight illuminance tended to
decrease the light-trap catch, however, increased air temperature was
associated with an increase in light-trap catch. These effects varied depending
on family and species.
A final experiment used a remote sensing technique to estimate light-trap
efficiency. A 10 cubic metre volume around the light-trap was observed using a
video camera. Moth tracks recorded were classified into New Arrivals, Passers
By and Local Flights. The number of these tracks was compared to the lighttrap
catch so that efficiency estimates could be obtained. Results suggested
that at ground level, 125 watt Mercury-Vapour light-traps are only 20 %
efficient within this 10 cubic metre volume.
