Incidence of Anagrus obscurus (Hymenoptera: Mymaridae) egg parasitism on Calopteryx haemorrhoidalis and Platycnemis pennipes (Odonata: Calopterygidae, Platycnemididae) in Italy

摘要

Very little is known about the incidence of egg parasitoids in odonates, perhaps becauseOdonata eggs are well protected in stems or leaves, sometimes below water. In CentralItaly (Pontecorvo, Frosinone province) two damselflies, Calopteryx haemorrhoidalisand Platycnemis pennipes occur at high densities. In August 2007 we collected 30 stemsof the aquatic plant Potamogeton sp. used as substrate for oviposition and incubatedeggs in the laboratory. Most stems (24 for C. haemorrhoidalis and 23 for P. pennipes)contained odonata eggs. Parasitoids emerged from 12 stems, with a mean parasitism of2% for C. haemorrhoidalis and 6% for P. pennipes, and a maximum of 14% and 50%,respectively. Furthermore, we observed egg-laying of 19 females of C. haemorrhoidalisand 11 of P. pennipes, and marked the stems where oviposition was observed. Clutchesremained in the river for 5 days and were then collected and incubated. Parasitoidsemerged from 11 stems out of 30, with an average parasitism of 8% for C.haemorrhoidalis and 3% for P. pennipes (maximum of 50% and 29%, respectively). Allparasitoids belonged to the family Mymaridae, and were identified as Anagrus(Anagrus) obscurus Förster, 1861, sensu Soyka, 1955. This is the first time that suchspecies is described as an egg parasitoid of odonates, and that an egg parasitoid of C.haemorrhoidalis and P. pennipes is identified. Our data suggest that egg parasitismmight be a significant selective factor for both odonates in the studied locality, affectingfemale oviposition behaviour.