Comparing Consequences Of Conspecific And Congeneric Competition For The Native Coccinella Novemnotata (Coleoptera: Coccinelidae)

Three laboratory experiments were conducted to better understand the impact of an introduced coccinellid species, Coccinella septempunctata (C7), on a now rare native species, C. novemnotata (C9), which, since the mid 1980s, has undergone drastic declines following the establishment of the former. In the first experiment, larvae of C7 and two populations of C9 were reared interspecifically and intraspecifically (C9 only) in pairs through adult eclosion at two aphid prey densities. C7 reduced the survival and increased the time-to-adult eclosion of both populations of C9. Additionally, C9 survival began decreasing sooner interspecifically than intraspecifically. In the second experiment, C9 survival and adult weight increased as C9 became more mature in development to C7. In the third experiment, adult C7 consumed fewer eggs than did C9 but more of C9 than C7 eggs were consumed. Thus, not only is interspecific competition potentially a threat to C9, but also cannibalism of C9 eggs