Study on predation preference of Harmonia axyridis (Pallas) and Adonia variegata (Goeze) on red and green color morph pea aphids

In order to explore the inhibition effect of Harmonia axyridis (Pallas) and Adonia variegata (Goeze) on red and green pea aphids (Acyrthosiphon pisum Harris) populations and their predation preferences, pea aphids with total densities of 90 head dish^-1, 120 head dish^-1 and 150 head dish^-1 for H. axyridis, and 42 head dish^-1, 60 head dish^-1 and 78 head dish^-1 for A. variegate were used to determine predation preferences of H. axyridis and A. variegata on two color morphs of pea aphids. The results showed that when red and green pea aphids co-existed, female adults of H. axyridis were insensitive to red morph in low and medium total prey densities (90 head dish 1 and 120 head dish^-1), sensitive to red morph in high total prey density (150 head dish^-1), and insensitive to green morph in all total prey densities. Female adults of H. axyridis also variably switched to red pea aphids in different total prey densities, showing zero switch in 90 head dish^-1 density, and negative switch in 120 head dish^-1 and 150 head dish^-1 densities. However, female adults showed zero switch to green morph. When red and green pea aphids co-existed, female adults of A. variegate were insensitive to red and green morphs pea aphid in all total prey densities. Female adults of A. variegata also variably switched to the two morph pea aphids in different total prey densities, showing zero switch in 42 head dish^-1 density, and negative switch in the 60 head dish^-1 and 78 head dish ^-1 densities. Therefore while female adults of A. variegata had no obvious preference for the two morphs of pea aphids, female adult of H. axyridis had no preference for the two morphs of pea aphids in lower population density but had positive preference for red morph in higher population density. The results suggested that dominant natural enemies (ladybird) were among the many factors for the changes in the populations of the two types of color of pea aphids.