Evaluating risk to native Uroleucon aphids from predation by non-native lady beetles

Aphids in the genus Uroleucon Mordvilko are native herbivores that feed on goldenrod (Solidago spp.) and other Compositae in North America.  The aphids are potential prey for a wide variety of natural enemies, including native and non-native species of lady beetles (Coleoptera: Coccinellidae).  Non-native lady beetles have been intentionally introduced to aid control of pest aphids in cropland, but some (e.g. Coccinella septempunctata and Harmonia axyridis) have been observed to prey upon Uroleucon aphids in natural and semi-natural settings, raising concerns about their nontarget effects on native aphids.  The objective of this study was to estimate non-target risk to Uroleucon aphids from non-native lady beetles.  Risk from non-native lady beetles was estimated by determining incidence of non-native lady beetles within naturally occurring, Uroleucon-infested patches of goldenrod and marsh elder in eastern South Dakota during 2009 and 2011, and by evaluating consumption of Uroleucon aphids by lady beetles in no-choice laboratory tests.  Although lady beetles readily consumed Uroleucon aphids in no-choice laboratory tests, they were infrequently associated with natural infestations of the aphids within relatively small patches of goldenrod and marsh elder that were sampled one or more times at several sites.  Low incidence of predation by lady beetles on naturally-occurring populations of Uroleucon spp. over multiple sites and times indicates that non-native lady beetles pose a relatively minor non-target risk to these native aphids.