seasonal changes of hippodamia variegata populations and its parasitism by dinocampus coccinellae in alfalfa fields of hamedan

ladybird hippodamia variegata (goeze) (coleoptera: coccinellidae) has been reported from many parts of iran, has an important factor on equilibrium and natural regulation of acyrthosiphon pisum (harris) (hem.: aphididae) population in alfalfa. determining the population seasonal change of h. variegata and its parasitism rate by the most important parasitoid species was the aim of this study. the samplings were done from april to october, 2010 at research filed of bu-ali sina university, dastjerd (hamedan province) (ca. 4.5 ha of alfalfa var. hamedani) where was intensively infested by acyrthosiphon pisumharris. every week, h. variegata adults were collected by sweep netting and totally 400 samples were brought back to the laboratory. population peakof h. variegata coincided with second and approximately third alfalfa cutting.the sex ratio of h. variegata (male: female) was calculated 1: 1.12. the most important parasitoid species of this predator was dinocampus coccinellaeschrank (hym.: braconidae) that its mean parasitism rate was %30.15 from september to november 2010. therefore, considering nearly the permanent presence of this predator in alfalfa fields and necessity of conserving and supporting native ladybirds, this study showed the importance of h. variegata population change and some influencing factors.