Susceptibility of immature monarch butterfly, Danaus plexippus (Lepidoptera: Nymphalidae: Danainae), to predation by Harmonia axyridis (Coleoptera: Coccinellidae)

The potential for a classical biological control agent, Harmonia axyridis (Pallas), to have non-target effects on populations of the monarch butterfly, Danaus plexippus (L.), was examined using no-choice predation studies under laboratory and caged field conditions. Three separate laboratory functional response experiments were conducted with adult and larval H. axyridis preying on immature D. plexippus. Nonlinear functional responses for third instar H. axyridis preying on D. plexippus eggs and first instars reached plateaus at about 25 and 15 prey consumed per day, respectively. A linear response resulted for adult H. axyridis preying on D. plexippus eggs. Potted Asclepias syriaca L. placed into large field-cages were infested with first instar D. plexippus and third instar H. axyridis. Survival of first instar D. plexippus was significantly lower in cages with H. axyridis larvae than in cages without H. axyridis larvae. The present experiments identify H. axyridis as a potential stressor to populations of D. plexippus. Further research is needed to assess the likelihood of D. plexippus exposure to H. axyridis in the field and to quantify the likelihood of H. axyridis having an adverse effect on D. plexippus in the presence of other prey, particularly aphids. These data could be used to develop an ecological risk assessment.