Locomotion ability variation among instars of the bean bug, Riptortus pedestris (Fabricius) (Heteroptera: Alydidae) nymphs.

The nymphal locomotion ability (walking distance) of the stenophagous bean bug Riptortus pedestris (Fabricius) was studied in each instar. We measured the walking distance using two systems. The walking distance in photophase was measured for 6 h using a tracking system with a charge coupled device (CCD) camera and computer software. The daily activity of nymphs was measured by an actograph system counting the number of infrared beam intercepts. The actograph data were converted to distance using a linear regression against the data of the tracking system. The longevity of nymphs without food was also studied to estimate the potential walking distance. Using both the tracking and actograph systems, it was determined that first instars walked less than the other instars (only 10.7 m within 6 h). The second to fifth instars could move 20-25 m within 6 h, and this distance did not differ among instar. This indicates that first instars seldom move after hatching in the field. The walking distance for 24 h varied and was greatest for the third instars (80.8 m). The potential longevity of nymphs was found to increase with instar age. Potential locomotion ability (walking distance for 24 hxpotential longevity) was high in the third to fifth instars (approximately 340 m). The potential locomotion ability for the second instars was relatively low compared with the elder instars (approximately 180 m). From these results, nymphs of R. pedestris seem to adapt by identifying feeding site locations after hatching and elder instars may be able to find a novel feeding site after the degradation of previous habitat.