Method of using kites to carry tow nets in the upper air for sampling migrating insects and its application to radar entomology

Insects migrating above the surface boundary layer were efficiently and economically sampled over long periods using a large diameter tow net suspended beneath a kite. In a series of trials in Australia, sequential samples were obtained by day and night at predetermined altitudes, in the range 50–500 m. The net was raised and lowered independently of the kite, so that when conditions were calm in the lower atmosphere the kite could remain aloft in the geostrophic airflow. Potential contamination of insects flying below the sampling height was minimised during net ascent, by reducing the airflow through the net. A radio-operated net-closing and releasing mechanism prevented contamination during the free fall of the net. The catch was converted to absolute values of aerial density and migration rate or flux. Aerial sampling was originally developed to identify upper air migrants under observation by the CSIRO entomological radar and to provide quantitative measurements of those species too small to be individually detected by radar. The technique was subsequently operated independently of radar to quantify microinsect migrations, but not those of macroinsects because of their relatively low catch rate.