Preliminary observations of flight activity of Trichoptera in the southern Cape, South Africa

Abstract

In a study on flight activity it was observed that Trichoptera were attracted to a superactinic or UV light at a site along the lower Groot River near Nature’s Valley in the Western Cape, South Africa. The frequency of insects passing selected fixed points in space was recorded photographically, after dusk, on 44 days between October 2011 and May 2012. All digital images of insects were identified to species, where possible, and abundance of species over selected time periods was determined. Water and air temperature, relative humidity, barometric pressure, wind direction and speed were continuously recorded during each recording event. Total dissolved solids (TDS), electrical conductivity, pH, the percentage of cloud cover, rain at the time of the survey, and rainfall prior to the survey, were all recorded. The dominant species during all surveys, Athripsodes bergensis Scott, revealed a modal peak of flight activity around 50 minutes after sunset which was strongly influenced by climatic variation. The presence of egg masses carried by females was observed from the middle of November through March, with the highest percentage of females with egg masses found from late November to early December. Other species of Trichoptera that were recorded flying appeared later after sunset than did A. bergensis. Statistically the most important factor influencing flight activity was the time in minutes after sunset. Clear, cloudless conditions resulted in reduced flight activity. Information on flight activity can be used to determine the optimum weather conditions and times for collecting Trichoptera when using light sources.