9 Abstract As an effective generalist predator of aphids and other hemipteran pests 10 H. axyridis has been a successful biological control agent. However, the very functional 11 traits that have contributed to its success in this regard also implicate it as an intraguild 12 predator that poses a significant risk not only to the diversity of other natural enemies of 13 Hemiptera (and their associated ecosystem services), but to biodiversity more widely. In 14 this paper we will specifically review the existing data on intraguild predation involving 15 H. axyridis, and consider the strength and symmetry of such interactions both within its 16 native guild and within exotic guilds where it has established as an invasive alien. We will 17 use these studies to interpret the observed population declines in predator diversity in the 18 field, predict species at risk in regions not yet invaded and consider implications for 19 resulting ecosystem services. We will also indicate gaps in our knowledge that require 20 further study in order to identify opportunities for mitigation.21 Keywords Coccinellidae Á Harmonia axyridis Á Aphidophagous guild Á 22 Intraguild predation Á Predators Á Parasitoids Á Pathogens Á Ecosystem services 23 Introduction 24 Terrestrial ecosystems support a diversity of species that are directly and indirectly linked 25 to each other within food webs that span multiple trophic levels. Natural enemy species (in 26 the context of this paper we will collectively call these 'predators' as they all have a trophic 27 relationship with their hosts/prey) contribute to the population regulation of species in both
9 Abstract As an effective generalist predator of aphids and other hemipteran pests 10 H. axyridis has been a successful biological control agent. However, the very functional 11 traits that have contributed to its success in this regard also implicate it as an intraguild 12 predator that poses a significant risk not only to the diversity of other natural enemies of 13 Hemiptera (and their associated ecosystem services), but to biodiversity more widely. In 14 this paper we will specifically review the existing data on intraguild predation involving 15 H. axyridis, and consider the strength and symmetry of such interactions both within its 16 native guild and within exotic guilds where it has established as an invasive alien. We will 17 use these studies to interpret the observed population declines in predator diversity in the 18 field, predict species at risk in regions not yet invaded and consider implications for 19 resulting ecosystem services. We will also indicate gaps in our knowledge that require 20 further study in order to identify opportunities for mitigation.21 Keywords Coccinellidae Á Harmonia axyridis Á Aphidophagous guild Á 22 Intraguild predation Á Predators Á Parasitoids Á Pathogens Á Ecosystem services 23 Introduction 24 Terrestrial ecosystems support a diversity of species that are directly and indirectly linked 25 to each other within food webs that span multiple trophic levels. Natural enemy species (in 26 the context of this paper we will collectively call these 'predators' as they all have a trophic 27 relationship with their hosts/prey) contribute to the population regulation of species in both
Declines in native aphidophages in North America have been linked to intraguild predation (IGP) by the invasive coccinellid Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). It is feared that many British species will face a similar fate following the recent establishment of H. axyridis in the UK. Meanwhile, H. axyridis exists in apparent ecological equilibrium with other members of its guild in Japan. The impact of H. axyridis on British coccinellids is uncertain but intraguild predatory interactions do occur, particularly amongst immature stages. This study investigates IGP between immature stages of H. axyridis and various British and Japanese coccinellids. The only asymmetric IG predator of H. axyridis at first instar was Anatis ocellata (Linnaeus). Harmonia axyridis engaged in symmetric IGP with Coccinella septempunctata Linnaeus, Calvia quatuordecimguttata (Linnaeus), Harmonia quadripunctata (Pontoppidan) and Eocaria muiri Timberlake, but was the asymmetric IG predator of all other species studied. The level of IGP was high between fourth instar larvae, and frequently biased towards H. axyridis, except in the case of A. ocellata, which again was the only IG predator of H. axyridis. In interactions between fourth instar larvae and pre-pupae, IGP was unidirectional towards H. axyridis for all species except A. ocellata, which acted as both IG predator and IG prey. Pupae were better protected against IGP than pre-pupae but most species were still susceptible to attack by H. axyridis, although IGP was symmetric with A. ocellata, and H. quadripunctata pupae were never attacked. The differences in susceptibility of the various species and developmental stages to IGP by H. axyridis are discussed in relation to physical defence structures. We find no evidence that Japanese species have superior defences to British ones and suggest that behavioural strategies may enable co-existence in the native range. We discuss the relevance of IGP by H. axyridis to the species it is likely to encounter in Britain.
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