Contrasting responses to object orientation and illumination by the blowflies Chrysomya chloropyga and Lucilia sericata

The alighting response of two species of blowfly, Chrysomya chloropyga (Weidemann) and Lucilia sericata (Meigen) (Diptera: Calliphoridae), were considered in relation to the orientation and illumination of a flat, oblong visual object. A strong response to orientation was displayed by L. sericata with the greatest number alighting on the vertical object; there was no significant effect of orientation on the number of C. chloropyga which alighted. Both species alighted preferentially on the more strongly illuminated side of a vertical object. With the object horizontal and more strongly illuminated from below, C. chloropyga again landed on the most brightly illuminated side. In contrast, reducing the brightness on the upper surface of the horizontally-suspended object reduced the number of L. sericata alighting on the upper surface but also reduced the overall catch, suggesting that for L. sericata the response to the illumination of a surface does not outweigh its response to its orientation. The implications of these results for the development of trapping technology for the monitoring or control of these economically important pest species is discussed.