فائزه طاوسی اجود

Although herbivores often encounter with many predator types, most experimental predation studies have focused on the effects of single predator on its prey. Recent researches have presented new insight about the effects of multiple predators on their preys. The effects of different types of predators may affect the population of prey in a quite complex way. To perceiving the influence of combined usage of predators on consumption ratio, we investigated the intraguild predation (IGP) between 3rd instar larvae of Episyrphus balteatus De Geer (Diptera: Syrphidae) with the 2nd and 3rdinstar larvae of Hippodamia variegata Goeze (Coleoptera: Coccinellidae) on the sweet pepper seedlings in the presence of 3-days old nymphs of cotton aphid, Aphis gossypii Glover (Hem.: Aphididae). Predator rearing and IGP experiments were carried out under laboratory conditions (22± 2°c, 60±10% RH and 16L: 8D photoperiod). The treatments included 2nd and 3rd instar larvae of H. variegata and 3rd instar larvae of E. balteatus alone, their combinations and control (without predators). All experiments had 10 replicates. The expected and observed proportions of killed aphid were calculated for each treatment. Comparison of these proportions indicated that the probabilityof aphid predation is reduced in multiple treatments than single usages. In the most cases, the third instar larvae of E. balteatus alone were more efficient than H. variegata 2nd and 3rd instar larvae both in combined and single situations.

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.