Dispersion and spatial orientation of Gerris remigis in response to water current: a comparison of pre‐ and post‐diapause adults

. The movements and orientation of adult Gerris remigis Say (Hemiptera; Gerridae) were examined in an artificial stream to determine the mechanisms by which these stream‐dwelling waterstriders compensate for and/or avoid downstream drift, and to compare the movement tendency of pre‐ and post‐diapause adults. G. remigis respond to current by turning to face directly into the current (rotational orientation), intermittently rowing against the current (translational orientation), and moving onto land to avoid the current. These rotational and translational responses enable G. remigis to maintain their positions in currents =S10 cm s ‐1 . However, avoidance increases with current speed, and few animals are found where currents exceed 10 cm s ‐1 . These observations correlate well with the observed distribution of adult G. remigis in a natural stream. Comparisons between life stages reveal that post‐diapause adults move more, and are more susceptible to drift than pre‐diapause adults. Post‐diapause adults also avoid even slight currents (<5 cm s _1 ) by seeking land, while pre‐diapause adults do not show a significant preference for land until currents exceed 10 cm s ‐1 . These data suggest that previously reported differences in the movement tendency of pre‐ and post‐diapause adults in the field may reflect physiologically‐based behavioural differences between these two life stages rather than merely direct responses to environmental cues.