Post-copulatory ”resting” in Orthetrum coerulescens (Fabricius) and some other Libellulidae: time for ”sperm handling”? (Anisoptera)

Mated female Orthetrum spp. carry very small volumes of stored sperm compared to many other libellulids. In several Orthelrum spp. and in a few other species, most copulations are followed by periods of "rest" (PCRs) lasting from one to several minutes during which the male and female perch close together before the start of oviposition. During PCRs males sometimes show "aggressive” behaviour towards their mates, apparently attempting to induce them to oviposit. Experimental and natural disturbances of female O. coerulescens during PCRs were found to excite at least brief oviposition bouts in 10 out of 48 cases. Females captured during or after copulation could be induced to oviposit large egg clutches. Several possible explanations for PCRs are considered: they may allow females to assess predator pressure at the oviposition site, to judge a male’s guarding capacity, or to "handle” sperm either mobilising it for fertilisation or selecting it according to the quality of their mates. PCRs do not seem to be needed for egg preparation.