Choice of perch by the water stick insect

Several characteristics of an adequate perch site for the water stick insect, Ranatra linearis L. (Heteroptera: Nepidae) and variations of perch preference during post-embryonic development have been investigated. Under laboratory conditions adults preferred reeds (Calamagrostis epigeros and Phragmites communis ) to the other plant species presented and avoided rushes (Juncus sp.). These results confirmed Waitzbauer's (1976) observations that showed that Ranatra preferred Phragmites communis over Utricularia vulgaris in the field. During development, preference for one type of plant changed first from Lemna to Elodea , then after the 4th instar, from Elodea to reeds. Predator size in relation, to perch size did not appear to be the main factor influencing these changes of preference. Perch colour preference changed during development from green to brown. In addition, adults preferred vertical perches to horizontal ones, but approximately as many 1st and 2nd instar larvae were found on vertical perches as on horizontal ones. Renatra usually perched parallel to their support: in the majority of observations the longitudinal axis of the body formed an angle of between - 5° and + 15° with the vertical plane at all developmental stages.