The choice of oviposition sites by hoverfly females determines the fate of offspring especially in those aphidophages whose newly hatched larvae have limited dispersal ability. This behavior is by several factors that their effects on oviposition behavior of some species have received little attention. In this study, we examined oviposition responses of the predatory Eupeodes corollae to different sizes of aphid colony in three aphid-plant systems and to the presence of eggs or larvae of or competitors in oviposition sites. Results showed that the predatory females avoided laying eggs in aphid-uninfested plants. But in cases of availability of infested plants, they laid their eggs in proportion of aphid colony sizes. In response to the presence of or competitors, females laid fewer eggs at sites where there were either larvae or eggs of or competitors. Moreover, it was shown that the presence of either larva of the or competitor in the colony of the test aphid had stronger on oviposition avoiding of E. corollae females compared to the presence of either one day old egg of a or competitor. These may help to understand the mechanisms of decision-making by the ovipositing females of the E. corollae. However, a full understanding of oviposition responses of E. corollae as a biocontrol agent of aphids to the presence of and competitors in aphid colonies requires follow-up research under conditions.

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