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Abstract:
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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. |