Biotic interactions between Eriopis connexa and Hippodamia variegata, a native and an exotic coccinellid species associated with alfalfa fields in Chile
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Human-assisted introductions, including those in the context of biological control, are considered to be one of the most important factors of global environmental change. However, the mechanisms underlying environmental changes, such as a decrease in the relative abundance of native species, are poorly understood. Since the introduction of the ladybird beetle, Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae), in Chile in the 1970s for biological control of aphids, a reduction in the relative abundance of the native ladybird beetle Eriopis connexa (Germar) has been noticed. To explore the role of cannibalism, intraguild predation (IGP) or competition as possible mechanisms that might increase dominance of H. variegata over E. connexa, several laboratory experiments were carried out. The native and the exotic species were very similar in their voracity and biotic interactions. Although H. variegata was able to maintain constant reproductive performance, E. connexa reproduction decreased at lower densities of aphids, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae). The impacts of cannibalism, IGP, and competition exerted by these species were very symmetrical in both larvae and adults. We conclude that these biotic factorsmay not fully explain the increase in relative abundance of H. variegata. The higher sensitivity of E. connexa to prey patch size, along with other factors such as chemical-mediated negative interspecific interactions may be operating in alfalfa fields, changing the composition of associated coccinellid assemblages.
DOI: DOI: 10.1111/j.1570-7458.2011.01202.x