Field data collected from the major citrus-producing regions of Florida over the past five years indicates that the introduced ladybeetle, Harmonia axyridis Pallas, has increased in abundance at the expense of the formerly dominant Cycloneda sanguinea (L.). What is known of the diet breadth, habitat preferences and thermal thresholds for development of these two species indicates considerable niche overlap. Harmonia axyridis has many intrinsic competitive advantages over C. sanguinea that include larger body size, higher fecundity and fertility, and a lower intrinsic rate of larval cannibalism. In laboratory tests, adults and larvae of H. axyridis consumed eggs of C. sanguinea more readily than vice versa. Similarly, H. axyridis adults fed readily on both conspecific and heterospecific larvae, whereas only 15% of C. sanguinea adults consumed a larva of H. axyridis over a 24 h period. Larvae of H. axyridis were more aggressive against larvae of C. sanguinea than vice versa in laboratory tests and larval contests were almost always won by H. axyridis, even when the C. sanguinea larva was 2 days older and 2-3 times as large. In choice tests, larvae of both species preferred to feed on larval corpses of C. sanguinea than on those of H. axyridis. Larvae of H. axyridis were capable of completing development exclusively as intraguild predators on C. sanguinea larvae, whereas the reverse was not true. The data suggest that H. axyridis is a highly evolved interspecific competitor, whereas C. sanguinea is adapted more to intraspecific competition and has few defenses against H. axyridis. Harmonia axyridis would appear to be in the process of competitively displacing C. sanguinea within the citrus ecosystem in Florida.
Species 1: Coleoptera Coccinellidae Harmonia axyridis
Species 2: Coloeptera Coccinellidae Cycloneda sanguinea
Keywords: competition, intraguild predation
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