Trophic Interactions Between Two Herbivorous Insects, \u3cem\u3eGalerucella calmariensis\u3c/em\u3e and \u3cem\u3eMyzus lythri\u3c/em\u3e, Feeding on Purple Loosestrife, \u3cem\u3eLythrum salicaria\u3c/em\u3e, and Two Insect Predators, \u3cem\u3eHarmonia axyridis\u3c/em\u3e and \u3cem\u3eChrysoperla carnea\u3c/em\u3e

Abstract

The effects of two herbivorous insects, Galerucella calmariensis Duftschmid and Myzus lythri L. (Coleoptera: Chrysomelidae), feeding on purple loosestrife, Lythrum salicaria L. (Myrtiflorae: Lythraceae), were measured in the presence of two insect predators, Harmonia axyridis Pallas (Coleoptera: Coccinellidae) and Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae). A greenhouse cage experiment examined the direct effects of these predators on these herbivores, and indirect effects of predation on aboveground biomass, defoliation, number of leaves, and internode length. Eight treatment combinations with G. calmariensis, M. lythri, H. axyridis and C. carnea were applied to caged L. salicaria. The experiment ended when G. calmariensis adults were observed, 11 to 13 days after release of first instar G. calmariensis. G. calmariensis larvae alone removed significant amounts of leaf tissue and reduced the number of L. salicaria leaves. Predators did not reduce levels of defoliation by G. calmariensis. C. carnea had no effect on G. calmariensis survival, but H. axyridis reduced G. calmariensis survival in the presence of M. lythri. Both predators reduced the survival of M. lythri. This short duration greenhouse study did not demonstrate that predator-prey interactions altered herbivore effects on L. salicaria