Walking locomotion in <scp> <i>Triatoma infestans</i> </scp> : An approach that explores the relationships between leg morphometry and locomotor activity

The active dispersal of triatomines has great epidemiological importance as it constitutes the main mechanism of colonization and reinfestation. Walking dispersal and its locomotor system have been little studied in triatomines. The aim of this study was to characterize the locomotor activity of fifth-instar nymphs of T. infestans and link it to morphometric characteristics of the body, legs and their articles. For locomotor activity, each insect was placed on a circular arena and was filmed while walking freely for 10 min. The variables analysed were distance travelled (TD), movement time (TM) and effective speed (ES). Photographs were then taken of the body, the right legs and their articles, and morphometric tools were used to obtain linear, size and shape metrics. On average, a nymph walked 470 cm and moved for 5 min at an ES of 98 cm/min. Positive correlations were observed for TD-TM and TD-ES. Body and leg lengths correlated mainly with ES. Linear measurements showed the same pattern for each leg: TD correlated with femur and tibia length, and coxa width; TM did not show correlation; and ES correlated with femur and meron length, and coxa width. Size variables showed different associations for each leg. Shape variables revealed the associations of the meron with TD for foreleg and of the femur with TD for mid and hind leg. The locomotor activity of fifth-instar nymphs of T. infestans was highly variable in time and distance, with a relatively constant speed. The results suggest that linear dimensions are not linked to the function of each leg, but rather the size and shape of the articles. Thus, the specific function of the foreleg during walking would be linked to the size and shape of its proximal part, while that of the hind leg would be linked to the size and shape of its distal part. Our results provide a solid understanding of how the form of the locomotor structures is linked to walking performance.