Intraguild predation of immature stages of British and Japanese coccinellids by the invasive ladybird Harmonia axyridis

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.     

Suitability of exotic and native lady beetle eggs (Coleoptera: Coccinellidae) for development of lady beetle larvae

Predation upon lady beetle (Coleoptera: Coccinellidae) eggs in the field is most often instances of egg cannibalism by larvae or adults while the majority of the remaining predation events upon coccinellid eggs is done by other species of Coccinellidae. Thus the recent introduction and establishment of Harmonia axyridis in the US could negatively affect native species of Coccinellidae via egg predation. However, little is known regarding the suitability of interspecific coccinellid eggs as a food source for larval development. In this study, it was found that native first or third instar Coleomegilla maculata and Olla v-nigrum larvae were incapable of surviving to the adult stage when provided solely exotic H. axyridis eggs. In stark contrast, H. axyridis larvae survived equally well when cannibalizing eggs or eating eggs of either native species. When C. maculata and O. v-nigrum were grouped as ‘native’ and compared with the exotic H. axyridis, more native eggs were attacked than exotic eggs and a higher percentage of eggs was attacked by H. axyridis larvae. Native and exotic larvae attacked a similar percentage of native eggs but native larvae attacked significantly fewer exotic eggs than did exotic larvae. These data suggest that H. axyridis may prey upon the eggs of these native species, when encountered in the field, compared with the likelihood of the native species preying upon H. axyridis eggs. Therefore, eggs of the native species C. maculata and O. v-nigrum will continue to be subjected to cannibalism and also to possible predation by other native species and the exotic H. axyridis.     

Decline in native ladybirds in response to the arrival of Harmonia axyridis: early evidence from England

1. Harmonia axyridis (Coleoptera: Coccinellidae) is an invasive non‐native ladybird in Europe, where it was introduced as a biological control agent of aphids and coccids. 2. This study assesses changes to ladybird species assemblages, in arboreal habitats, over a 3‐year period encompassing the invasion phase of H. axyridis in eastern England. The effects of H. axyridis and other factors (weather and prey availability) on native ladybirds are assessed. 3. Harmonia axyridis increased from 0.1% to 40% of total ladybirds sampled, whilst native aphidophagous species declined from 84% to 41% of total ladybirds. The actual number of native aphidophagous ladybirds per survey decreased from a mean of 19.7 in year 1, to 10.2 in year 3. 4. Three ladybird species in particular experienced declines: Adalia bipunctata, Coccinella septempunctata, and Propylea quattuordecimpunctata. Harmonia axyridis was the most abundant species by the end of the study. 5. The decline in native aphidophagous ladybirds could be attributed to competition for prey and intraguild predation of eggs, larvae, and pupae by H. axyridis. Physiological and behavioural traits of H. axyridis are likely to confer an advantage over native ladybird species.     

A sublethal effect on native Anthocoris nemoralis through competitive interactions with invasive Harmonia axyridis

1. The invasive ladybird Harmonia axyridis Pallas (Coleoptera: Coccinellidae) is implicated in declines of native ladybirds with intraguild predation identified as an underlying mechanism, however, less studied are the effects on non‐coccinellid predators. Intraguild predation between Anthocoris nemoralis Fabricius (Heteroptera: Anthocoridae) and H. axyridis and the relative effects of inter‐ and intraspecific competition on predators on potted Tilia cordata Mill. was investigated, at two aphid densities. 2. Intraguild predation was unidirectional in favour of H. axyridis in Petri dishes although a low level of ladybird egg predation by A. nemoralis occurred. However, on trees intraguild predation was rare. 3. A positive effect of aphid density on H. axyridis weight gain, and increased survival when reared with A. nemoralis on potted trees indicated stronger effects of intraspecific competition on H. axyridis. Consistent suppression of aphids by ladybirds revealed their superior competition for aphids. 4. Anthocoris nemoralis weight gain was reduced when reared with H. axyridis on potted trees, indicating a potential for a sublethal effect through interspecific competition. Survivorship of A. nemoralis did not differ between con‐ and heterospecific treatments, but high aphid density enhanced A. nemoralis survival. Overall, high mortality among nymphs across treatments suggested effects related to both inter‐ and intraspecific competition for resources. 5. Results provide evidence of a sublethal effect by invasive H. axyridis through resource competition, suggesting that where these predators co‐occur, competitive interactions for shared prey are more likely to affect A. nemoralis populations than intraguild predation by H. axyridis.     

Can Developmental and Behavioral Characteristics of the Multicolored Asian Lady Beetle Harmonia Axyridis Explain its Invasive Success?

Major impacts of biological invasions are widely recognized and underscore the need to understand the relation between life-history traits of invasive species and the invasion process. Growth of juveniles and adult survival of invasive species are key factors in invasion process. Life-history traits that increase juvenile fitness including increased rates of development and behavioral characteristics that facilitate competitive success such as increased predator efficiency and foraging ability may explain invasiveness of a species. Invasion of Harmonia axyridis Pallas (Coleoptera: Coccinellidae) in North America provides an opportunity to investigate life-history traits of juveniles of an invasive species. Here, we evaluate both developmental and behavioral traits that may explain the success of H. axyridis by comparing it to an ecologically similar indigenous species Coleomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae). Three points may contribute to the invasiveness of H. axyridis. First, development of H. axyridis was faster during the 2nd larval instar than C. maculata, a characteristic that may reduce vulnerability at young instars. Second, H. axyridis reached the 4th instar more rapidly than C. maculata. The 4th instar of H. axyridis was also characterized by higher predation efficiency with increased voracity, lethal contact and search efficiency of pea aphids Acyrthosiphon pisum. Finally, surprisingly, a 5th larval instar occured in 33% of the individuals of H. axyridis and was characterized by the same developmental time, but with increased voracity and weight gain compared to 4th larval instars, suggesting an increased fitness of these individuals. These developmental characteristics coupled with increased predation efficiency and behavioral characteristics enhanced the juvenile growth and predatory abilities of this species and may contribute to the invasive ability of H. axyridis.     

Estimation of mortality by entomophages on exotic Harmonia axyridis versus native Adalia bipunctata in semi-field conditions in northern Italy

A semi-field experiment was carried out in two peach orchards in northern Italy to assess mortality due to predators and parasitoids on the exotic coccinellid Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in comparison with the native coccinellid Adalia bipunctata L. (Coleoptera: Coccinellidae). The experiments were conducted in cages to avoid the possible escape of the exotic ladybird (not yet established in Italy). Two kinds of cage experiments were included: ‘exclusion cages’ (access by walking predators impeded) and ‘free cages’ (walking predators free to enter). The cages, containing all the stages of the two ladybird species, were placed in two localities and left for 24 h. All ladybird stages used for the semi-field experiments came from a laboratory rearing. The eggs of H. axyridis experienced less mortality than those of A. bipunctata. The ant workers were the most frequent predators in ‘free cages’ but A. bipunctata cannibalism on eggs was also detected. Larvae of both coccinellid species were predated equally but larval predation of L1 and L2 was higher in comparison to predation of L3 and L4. Pupae and adults of both exotic and native ladybirds were never attacked by predators. Predation on younger larval stages was higher in the ‘free cages’ in comparison with ‘exclusion cages’. No ladybird parasitisation was observed. The ‘free cage’ technique seems to provide a standardised and realistic estimation of predation impact but more studies are needed to evaluate ladybird parasitisation in semi-field conditions.     

Invasion history, habitat preferences and phenology of the invasive ladybird Harmonia axyridis in Belgium

Harmonia axyridis Pallas (Coleoptera: Coccinellidae) is native to Asia, and was widely introduced as a biocontrol agent of aphids and coccids in Europe and North America. In Europe, H. axyridis is considered to be an invasive alien species because of its potential to disrupt native ladybird communities. Since 1999, the Belgian Ladybird Working Group mapped all Belgian Coccinellidae and recorded data on substratum plants and habitat. The first feral H. axyridis population in Belgium was recorded in 2001, but the expansion rate is decreasing because it now colonised the whole country. Recorded occupancy in Belgium showed an average rate of increase of 189% between 2002 and 2006. In Belgium, H. axyridis occurred in a wide range of habitats, including those of high conservation value. However, habitat and land cover analysis showed that H. axyridis is more frequently found in urbanised landscapes than in semi-natural landscapes. A niche overlap analysis based on plant use data showed that the potential to affect native species is higher for generalist, deciduous and coniferous tree ladybird species than for heathland and wetland specialist species. Phenology data showed that H. axyridis is able to reproduce later in the year than native species. Based on recorded distribution, ecology and phenology, we discuss the potential of H. axyridis to disrupt native ladybird assemblages in Belgium.     

Biodiversity Loss following the Introduction of Exotic Competitors: Does Intraguild Predation Explain the Decline of Native Lady Beetles?

Exotic species are widely accepted as a leading cause of biodiversity decline. Lady beetles (Coccinellidae) provide an important model to study how competitor introductions impact native communities since several native coccinellids have experienced declines that coincide with the establishment and spread of exotic coccinellids. This study tested the central hypothesis that intraguild predation by exotic species has caused these declines. Using sentinel egg experiments, we quantified the extent of predation on previously-common (Hippodamia convergens) and common (Coleomegilla maculata) native coccinellid eggs versus exotic coccinellid (Harmonia axyridis) eggs in three habitats: semi-natural grassland, alfalfa, and soybean. Following the experiments quantifying egg predation, we used video surveillance to determine the composition of the predator community attacking the eggs. The extent of predation varied across habitats, and egg species. Native coccinellids often sustained greater egg predation than H. axyridis. We found no evidence that exotic coccinellids consumed coccinellid eggs in the field. Harvestmen and slugs were responsible for the greatest proportion of attacks. This research challenges the widely-accepted hypothesis that intraguild predation by exotic competitors explains the loss of native coccinellids. Although exotic coccinellids may not be a direct competitor, reduced egg predation could indirectly confer a competitive advantage to these species. A lower proportion of H. axyridis eggs removed by predators may have aided its expansion and population increase and could indirectly affect native species via exploitative or apparent competition. These results do not support the intraguild predation hypothesis for native coccinellid decline, but do bring to light the existence of complex interactions between coccinellids and the guild of generalist predators in coccinellid foraging habitats.     

Intraguild predation between the invasive ladybird Harmonia axyridis and non-target European coccinellid species

The coccinellid Harmonia axyridis (Pallas) has been used for augmentative and classical biological control in many environments. More recently it has invaded large parts of Europe and negative effects for native populations of aphidophagous coccinellids are beginning to emerge. Here we investigate intraguild predation (IGP) between H. axyridis and eleven native non-target European coccinellids, including less common species which have not been studied so far within this context of non-target effects. When first-instars of H. axyridis were paired with the native species, only Anatis ocellata (Linnaeus) and Calvia quatuordecimguttata (L.) were significantly superior to the former whereas H. axyridis was superior in three cases, i.e. against Aphidecta obliterata (L.), Coccinella septempunctata L. and Hippodamia variegata (Goeze). Non-significant results were obtained for all other pairings. Similar tests with the fourth larval instar revealed stronger IGP rates and H. axyridis was found to be superior in the interactions with Adalia bipunctata (L.), Adalia decempunctata (L.), A. obliterata, Calvia decemguttata (L.), C. quatuordecimguttata, C. septempunctata, H. variegata, Oenopia conglobata (L.) and Propylea quatuordecimpunctata (L.) whereas non-significant results were obtained for interactions with two other native species. Another experiment revealed that H. axyridis was able to prey more successfully upon egg of most native coccinellid species than vice versa. However, C. quatuordecimguttata eggs seem to be more protected against predation than those of the other species. Survival of first-instar H. axyridis was higher on conspecific eggs compared to eggs of any other species tested. Our results suggest that H. axyridis may become a threat to a wide range of native aphidophagous coccinellids sharing similar ecological niches except species showing high potential for chemical or physical protection.     

Negative dietary effects of Colorado potato beetle eggs for the larvae of native and introduced ladybird beetles

Aphidophagous ladybird beetles (Coleoptera: Coccinellidae) are attracted to and feed heavily on aphids, but many species will also feed opportunistically on other prey that they encounter. In potatoes (Solanum tuberosum L.) in Washington State, USA, coccinellids feed on both green peach aphids (“GPA,” Myzus persicae Sulzer) and eggs of the Colorado potato beetle (“CPB,” Leptinotarsa decemlineata Say). The guild of aphidophagous ladybirds includes two native species, Hippodamia convergens Guérin-Méneville and Coccinella transversoguttata Brown. Recently, an introduced species, Coccinella septempunctata L., has invaded and apparently displaced its native congener. A second exotic, Harmonia axyridis Pallas, has colonized the area and is becoming more abundant. We compared larval development of each species on a monotypic diet of GPA, a monotypic diet of CPB eggs, or a mixed diet of both GPA and CPB eggs. Our goal was to answer two questions: (1) do larvae of the four ladybird species benefit from including CPB eggs in their diet and (2) do the four ladybird species differ in their ability to utilize CPB eggs as prey? No larva of any species completed development on a pure diet of CPB eggs, and survivorship was highest for all species when they fed on a pure diet of GPA. One native species, H. convergens, and one exotic species, H. axyridis, exhibited significantly lower survivorship on a mixed diet of both CPB eggs and GPA, compared to a pure GPA diet; H. axyridis also took longer to develop from egg to adult when both prey were provided. Survivorship of the two Coccinella spp. was not altered by the inclusion of CPB eggs with GPA, although CPB eggs lengthened the development time of C. transversoguttata. Adult size was not consistently affected by diet for any of the coccinellids. Overall, no ladybird species benefited from the inclusion of potato beetle eggs in its diet. The two Coccinella species responded similarly to the inclusion of CPB eggs, and so we would not expect any difference in the success of coccinellid larval development in potato fields following the replacement of C. transversoguttata by C. septempunctata. Hippodamia convergens and H. axyridis, the two species whose survivorship was depressed by combining CPB egg and aphid prey, were also the two species that consumed the greatest number of CPB eggs during successful larval development. A comparison of total egg consumption by each species cohort suggested that displacement of the other species by H. axyridis would not alter CPB biological control, because the higher per capita feeding rate by H. axyridis larvae compensated for individuals’ greater mortality risk on a diet including CPB eggs.     

Overwintering, phenology and fecundity of Harmonia axyridis in comparison with native coccinellid species in Italy

Classical biological control is generallyunderstood as an environmentally safe practiceof insect pest management. However, questionshave been raised about possible negativeeffects for native species. As part of a riskassessment study a semi-field trial was carriedout in northern Italy in order to compare theoverwintering of the native species Propylea quatuordecimpunctata (L.) and Adalia bipunctata (L.) (Coleoptera:Coccinellidae) with the exotic Harmoniaaxyridis (Pallas) (Coleoptera: Coccinellidae).All the experiments were carried out from April1998 to April 2001. Harmonia axyridis wasable to overwinter successfully in northernItaly. Fecundity, oviposition rate, longevityand rate of increase of overwintering femaleswere calculated and the phenology of the threespecies was studied. Harmonia axyridisoverwintering mortality (31.9%) was lower incomparison with mortality of native species(68.9% for P. quatuordecimpunctata and61.3% for A. bipunctata). As aconsequence, post-overwintering rate ofincrease of the exotic species was higher.Longevity of overwintered females was similaramong the species. Mean fecundity of H. axyridis (783.8 eggs per female) was slightlyhigher than A. bipunctata (720.2 eggs perfemale), and much higher than P. quatuordecimpunctata (193.7 eggs per female). H. axyridis and A. bipunctatacompleted four generations and P. quatuordecimpunctata three generations in a year. The results show that H. axyridisappears to posses a high potential for establishment in Italy.     

Does nitrogen limitation promote intraguild predation in an aphidophagous ladybird?

Reciprocal intraguild predation occurs between the two aphidophagous ladybird beetles Coccinella septempunctata L. and Harmonia axyridis Pallas (Coleoptera: Coccinellidae). However, its direction is asymmetrical; H. axyridis generally acts as an intraguild predator, and C. septempunctata as an intraguild prey. According to Denno and Fagan's prediction that nitrogen shortages in predators may promote intraguild predation, it was hypothesized that growth of intraguild predator H. axyridis is more limited by nitrogen than that of intraguild prey C. septempunctata, and that H. axyridis growth is enhanced by feeding on C. septempunctata compared to feeding on aphids. To determine nitrogen‐limited growth in H. axyridis, the following two predictions were examined. First, it was predicted that the nitrogen content of H. axyridis would be higher than that of C. septempunctata when both feed on aphids. However, nitrogen content did not differ between the two ladybirds. Second, it was predicted that nitrogen‐use efficiency of H. axyridis would be lower than that of C. septempunctata. However, there was no significant difference between species. These results did not support the hypothesis that growth of H. axyridis is more limited by nitrogen than that of C. septempunctata. In addition, the present study showed that dry mass and nitrogen growth of H. axyridis were not enhanced, but rather decreased, by eating high‐nitrogen C. septempunctata, compared to eating low‐nitrogen aphids. Overall, the present study did not support the hypothesis that nitrogen shortages in predators may promote intraguild predation.     

Intraguild responses of aphid predators on apple to the invasion of an exotic species, Harmonia axyridis

The effects of the invasion ofan exotic predator, Harmonia axyridis(Pallas) (Coleoptera: Coccinellidae), wereinvestigated using three experiments on theecology of aphid predators on apple. Oneexperiment, 1992, was collected prior to theH. axyridis invasion, and two others,1996 to 1997 and 1999 to 2000, were collectedafter the invasion. Except for one year, 1999,H. axyridis was the dominant coccinellid,replacing the formerly dominant Coccinellaseptempunctata L. (Coleoptera: Coccinellidae),another exotic species. The dominance of H. axyridis was greater among larvae thanamong adults. There was no apparent effect ofthe H. axyridis invasion on abundance ofthe predator, Aphidoletes aphidimyza(Rondani) (Diptera: Cecidomyiidae) and apossible positive effect on the abundance ofchrysopids (Neuroptera: Chrysopidae). Principal component analysis indicated thatalthough individual species were affected, theoverall effect of H. axyridis invasion onthe predator guild as a whole was negligible. The data indicate that the interaction betweenthe two exotic species, H. axyridis andC. septempunctata, may be allowing nativecoccinellids to become more abundant on applethan when C. septempunctata was thedominant coccinellid.     

Functional Response ofColeomegilla maculata(Coleoptera: Coccinellidae) to Colorado Potato Beetle Eggs (Coleoptera: Chrysomelidae)

A comparative study of the functional response ofColeomegilla maculataDeGeer (Coleoptera: Coccinellidae) fourth instars was conducted under laboratory, greenhouse, and field conditions. In the laboratory, individual larvae were placed in 9-cm petri dishes for 24 h, with 1, 3, 5, or 7 Colorado potato beetle (Leptinotarsa decemlineata[Say]) (Coleoptera: Chrysomelidae) egg masses. Each egg mass was standardized at 15 eggs. In the greenhouse and field,C. maculatalarvae were provided with an equivalent of 0.5 to 35L. decemlineataegg masses/m²of potato leaf. Fourth instars ofC. maculataexhibited a type II functional response toL. decemlineataeggs under laboratory, greenhouse, and field conditions. Predator search efficiency was inversely related with prey density. The maximum mean attack rate (8.7 eggs) byC. maculatalarvae in the field was about half the mean attack rate in the laboratory (17.6 eggs) and greenhouse (20.1 eggs). The difference in prey density between the laboratory and field seems to have been a major contributing factor in determining the rate of predation, whereas differences in environmental conditions (e.g., temperature and possible alternate food) may explain the differences observed in the predation rate in the greenhouse and field.     

Impact of intraguild predation by adult Harmonia axyridis (Coleoptera: Coccinellidae) on Aphis glycines (Hemiptera: Aphididae) biological control in cage studies

The soybean aphid, Aphis glycines Matsumura, has become a principal arthropod pest of soybean in the U.S. since its first detection in 2000. This species threatens soybean production through direct feeding damage and virus transmission. A diverse guild of insect predators feeds on soybean aphid in Michigan including the exotic coccinellid Harmonia axyridis, the native gall midge Aphidoletes aphidimyza and the native lacewing Chrysoperla carnea. In addition to feeding on A. glycines some members of this guild may also engage in intraguild predation. These interactions may produce positive, negative, or neutral impacts on A. glycines biological control. We explored the impact of intraguild predation on soybean aphid population dynamics by comparing aphid populations in microcosms with either A. aphidimyza larvae or C. carnea larvae alone, with both a H. axyridis adult and either A. aphidimyza or C. carnea larvae, and without predators. When H. axyridis was present with larval A. aphidimyza or C. carnea, the lady beetle acted as an intraguild predator. However, intraguild feeding did not result in a release of aphid populations compared with microcosms containing only the intraguild and aphid prey. A similar result was found in field cages. Cages allowing large predators had reduced numbers of A. aphidimyza and C. carnea larvae but also significantly fewer aphids compared with predator exclusion cages. Thus, in both lab and field studies the direct impact of H. axyridis on A. glycines overcame its negative impact as an intraguild predator. Together, these studies indicate that while the exotic H. axyridis does act as an intraguild predator and may contribute to local declines in A. aphidimyza and C. carnea, it is also currently important in overall biological control of A. glycines.     

Harmonia axyridis in Great Britain: analysis of the spread and distribution of a non-native coccinellid

Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is native to Asia, and was widely introduced as a biocontrol agent of aphids and coccids in Europe and North America. In Europe H. axyridis is considered to be an invasive alien species. Although not known to have been deliberately introduced to Great Britain, it was first recorded there in 2004, in south-east England. Harmonia axyridis arrived in Great Britain by various means, primarily from mainland Europe, but also from Canada. Extensive national and local media coverage, and a dedicated website (), facilitated public involvement in recording H. axyridis in Great Britain; in excess of 4,000 verified records of the species were received between 2004 and 2006. Through detailed mapping, the objective of our study was to quantify and analyse the spread of H. axyridis in its early stages of invasion in Great Britain. Our data shows that between 2004 and 2006, the species spread north through Great Britain at the rate of 58 km year^-1 and west at the rate of 144.5 km year^-1. In England H. axyridis spread north to Yorkshire and west to Cornwall by the end of 2006, and also reached Wales. Recorded occurrence (of one or more H. axyridis individuals at larval, pupal and/or adult stage) in 10 km squares in Great Britain was: 2004—51; 2005—149; 2006—447. Records of juvenile H. axyridis extend through most of the recorded British range of the species, and we present evidence of bi-voltinism in the population in 2006.     

Intraguild predation on the parasitoid Aphidius ervi by the generalist predator Harmonia axyridis: the threat and its avoidance

Interactions between natural enemies can be crucial for determining their overall control of pest species, yet the mechanisms that govern such interactions are often poorly understood. The risk of negative effects such as intraguild predation and the possibility of mitigating such risks are important components for ultimately determining the compatibility of biological control agents. We performed a group of experiments to determine whether the coccinellid Harmonia axyridis Pallas (Coleoptera: Coccinellidae) poses an intraguild threat to the parasitoid Aphidius ervi Haliday (Hymenoptera: Braconidae) and to see whether A. ervi is able to avoid predation by responding to the chemical tracks deposited by H. axyridis. We show that although H. axyridis does not readily consume A. ervi mummies, it preferentially consumes parasitized aphids over unparasitized aphids. We also show that A. ervi can defend against this threat by avoiding oviposition in the presence of H. axyridis chemical tracks. Aphidius ervi parasitized far fewer pea aphids Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) on plants [Vicia faba L. (Fabaceae)] with H. axyridis chemical tracks in a no‐choice environment at a single‐plant scale. Similarly, when parasitoids could move freely between plants with and without tracks, A. ervi parasitism was higher on plants without tracks. Behavioral observations of A. ervi foraging suggested that this might be because of reduced A. ervi attack rates and patch residence times in the presence of H. axyridis tracks. Despite a risk of intraguild predation by H. axyridis, our study suggests that A. ervi may be able to mitigate this risk by altering its behavior in response to chemical cues.     

Effect of size,extraguild prey and habitat complexity on intraguild interactions: a case study with the invasive ladybird <Emphasis Type="Italic">Harmonia axyridis</Emphasis> and the hoverfly <Emphasis Type="Italic">Episyrphus balteatus</Emphasis>

Intraguild predation (IGP) is a widespread interaction between predatory arthropods, and is influenced by several factors. The harlequin ladybird, Harmonia axyridis (Coleoptera: Coccinellidae), has frequently been reported as an intraguild predator of other Coccinellidae, but little is known about its interactions with other aphidophagous predators, including syrphids. This study investigated the incidence of IGP between H. axyridis and Episyrphus balteatus (Diptera: Syrphidae), the most abundant hoverfly species in Europe and a commercially available aphid biocontrol agent. The influence of size, presence of extraguild prey and habitat complexity were investigated through laboratory experiments in Petri dishes and on potted broad bean plants. In both types of arenas, IGP between H. axyridis and E. balteatus was found to be asymmetric, with the coccinellid in the majority of cases being the intraguild predator. There was a significant effect of size on the frequency of IGP. The efficiency of H. axyridis as an intraguild predator increased with the developmental stage. Early instars of E. balteatus were the most vulnerable to IGP. Pupae of either species were not attacked. In the presence of extraguild prey, the frequency of IGP was substantially reduced. However, IGP still occurred, mainly in combinations of older larvae of H. axyridis with first or second instars of E. balteatus. The size of the arena affected the incidence of IGP in combinations with second instars of E. balteatus, but not in combinations with third instars. Field research is needed to elucidate the ecological relevance of IGP among these predators.     

Ecology of <Emphasis Type="Italic">Harmonia axyridis</Emphasis> in natural habitats within its native range

Originally distributed in northeast Asia, Harmonia axyridis (Coleoptera: Coccinellidae) is now found throughout much of the temperate zone. In its native area, H. axyridis maintains stable populations in heterogeneous and temporary habitats because of its great ability to find prey and reproduce, coupled with density-dependent and self-regulatory population regulation. A negative correlation of H. axyridis on the biodiversity of the aphidophagous community has been observed in its native range. The decrease in biodiversity may be mainly caused by the wider range of habitats available to H. axyridis than to the coexisting species. From a theoretical perspective, density-dependent regulation of H. axyridis populations, e.g., cannibalism, may be more important in maintaining the H. axyridis-dominated system, probably than is intraguild predation. Habitat heterogeneity may also be important to the coexistence of H. axyridis and other predators in both native and invaded areas.     

Harmonia axyridis: What will stop the invader?

In recent years Harmonia axyridis (Pallas, 1773) (Coleoptera: Coccinellidae) has become a very popular insect among biological control practitioners and scientists, not only for its potential to be an efficient biological control agent but also because it is considered invasive. Individuals of this species were deliberately introduced into several countries for biological control of different arthropods pests. However the predator itself became an invasive species, affecting the dynamics and composition of several guilds through direct or indirect interactions with established species, including intraguild predation. In this paper we discuss the reasons why the species has a high invasiveness and what are the limits to invasion by this species. It is not clear if the invasiveness of the beetle is linked to its biological, ecological and behavioural abilities, or to other factors such as invasibility and interactions between the invaders, the noninvaders, and the habitat, which may in part explain the reasons of its success and help us to answer the question “what will stop the invader?” We also discuss the reason for the absence of the predator in the Azores islands. Despite the intentional introduction of H. axyridis in the Azores and the high number of individuals released, there are no records of this species in the wild, despite recent extensive sampling effort. In this paper we discuss the reasons for the apparent failure or the delay in establishment of the predator. One factor which may hamper the establishment of H. axyridis in some of the Azores islands is the absence of winter environmental conditions, mainly the temperature which is seldom lower than 12°C, essential for the induction of diapause. The lack of success in the establishment could be also related to functional diversity saturation, that is species saturation and competitive exclusion of H. axyridis by other previously established species may be operating.