Functional Response Of Harmonia Axyridis (Pallas) (Coleoptera:Coccinellidae) Preying On Mixed Prey

Biological control is an ecologically friendly way to manage pests.Predators are a group of key natural enemies often used in biological control program,while functional response was a classical method that has been widely applied to evaluate the efficiency of natural enemies including predators.Various factors including alternative prey and prey distribution could influence the foraging outcome of predators.Thus,to better understand the foraging efficiency of natural enemies,it is critical to evaluate predation functional response under relative natural conditions.Therefore,in this study,we used a three-species system to evaluate effort of alternative prey and the prey distribution on functional response of a generalist predator.The species include Hyalopterus arundinis,which is a common pest attack peach and peach trees in China,and the multicolored Asian ladybird Harmonia axyridis,which is a commonly used natural enemy against aphid in various crop systems,and a parasitoid,Ephedrus persicae,which is one of the common parasitoid attack H.arundinis.The functional response of H.axyridis preying on H.arundinis and aphid mummies parasitized by E.persicae was examined under laboratory condition across five experimental durations(1 h,2 h,6 h,12 h,and 24 h).In addition,four type of prey combinations were examined: aphids only,aphids/mummies mix at 4:1,1:1 or 1:4 ratios.We found that the functional responses of all bioassays were type II.Furthermore,for both aphid consumption and overall prey consumption(aphids + mummies),when the aphid/mummy ratios were 1:1 and 1:4,the 95% confidence intervals of adjacent functional response curves start overlapping,indicating the existence of aphid mummy could reduce the foraging efficiency of H.axyridis.When comparing functional responses of H.axyridis preying on H.arundinis under three types of prey distribution conditions,we found that aphid distribution could also alter the functional response of H.axyridis.Specifically,no statistical differences were observed between functional responses of aggregate and uniform or between aggregate and random treatments.However,the confidence intervals of functional response curves between uniform and random treatments were separated when aphid density was approximately above 40.Overall,both alternative prey and prey distribution could affect the predation efficiency of H.axyridis.Results of this study provide useful information for evaluating the efficiency of predators.Further filed experiments are required to evaluate the potential of predator under complex and dynamic predator-prey crop system.