Intra- and interspecific interactions between aphidophagous ladybirds: the role of prey in predator coexistence

Abstract

Cannibalism (CANN) and intraguild predation (IGP)may provide energy and nutrients to individuals and eliminate potential competitors. These negative competitive interactions could also affect the coexistence of predatory species. The co-occurrence of aphidophagous ladybird species in crops creates opportunities for CANN and IGP, especially when aphids become scarce. The Lotka–Volterra model predicts the coexistence of two species if intraspecific competition is stronger than interspecific interference interactions. <i>Cycloneda sanguinea</i> L. and <i>Eriopis connexa</i> (Germar) (both Coleoptera: Coccinellidae) coexist in sweet pepper crops in La Plata (Argentina) consuming mainly <i>Myzus persicae</i> (Sulzer) (Hemiptera: Aphididae). The present study used laboratory experiments to estimate levels of CANN and IGP by adults and larvae on eggs, and by adults on larvae, in both the presence and absence of prey (i.e., <i>M. persicae</i>), to explain the effect of prey on coexistence of these two predators. Levels of CANN by <i>C. sanguinea</i> and <i>E. connexa</i> were high in the absence of aphids, and decreased when prey was present. Intraguild predation was bidirectional and asymmetric. Adults and larvae of <i>E. connexa</i> were more voracious IG predators of <i>C. sanguinea</i> than vice versa, the former being the stronger IG predator and interference competitor. <i>Eriopis connexa</i> always won when larvae of the same instar were compared, whereas the larger larva always won when larvae were of different instars, regardless of species. In the presence of prey, CANN by both species decreased, but IGP by <i>E. connexa</i> on <i>C. sanguinea</i> remained high, suggesting that <i>E. connexa</i> could displace <i>C. sanguinea</i> via interspecific interference competition. Other factors potentially affecting the coexistence of <i>C. sanguinea</i> and <i>E. connexa</i> in sweet pepper crops are discussed.