Landscape composition influences patterns of native and exotic lady beetle abundance

Aim Coccinellid beetles are important predators that contribute to pest suppression in agricultural landscapes. Since the introduction of the exotic coccinellids Coccinella septempunctata L. and Harmonia axyridis Pallas into the USA, several studies have reported a decline of native Coccinellidae in agroecosystems. We aimed to investigate the influence of landscape composition on native and exotic coccinellid abundance within soybean fields. Location Iowa, Michigan, Minnesota and Wisconsin. Methods As part of a 2‐year study (2005–06) on the biological control of the soybean aphid, Aphis glycines Matsumura, we examined coccinellid communities in 33 soybean fields using yellow sticky card traps. Landscape heterogeneity and composition were measured at multiple spatial scales ranging 1–3.5 km from focal soybean fields where coccinellid sampling took place. Results Exotic species made up 90% of the total coccinellid community in Michigan soybean fields followed by Wisconsin (84%), Minnesota (66%) and Iowa (57%). Harmonia axyridis was the dominant exotic coccinellid in all states comprising 45–62% of the total coccinellid community, followed by C. septempunctata (13–30%). Two additional exotic species, Hippodamia variegata (Goeze) and Propylea quatuordecimpunctata (L.) were also found in the region. Overall, the most abundant native coccinellid was Hippodamia convergens Guerin‐Meneville; however, its abundance varied across the region, comprising 0% (Michigan) to 28% (Iowa) of the total coccinellid community. Landscape structure significantly influenced the composition of coccinellid communities in soybean agroecosystems. We found that native coccinellids were most abundant in low‐diversity landscapes with an abundance of grassland habitat while exotic coccinellids were associated with the abundance of forested habitats. Main conclusion We propose that grassland dominated landscapes with low structural diversity and low amounts of forested habitat may be resistant to exotic coccinellid build‐up, particularly H. axyridis and therefore represent landscape‐scale refuges for native coccinellid biodiversity.     

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.     

Impact of fruit feeding on overwintering survival of the multicolored Asian lady beetle, and the ability of this insect and paper wasps to injure wine grape berries

The establishment of the multicolored Asian lady beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), in North America has resulted in negative impacts on fruit production. We investigated the overwintering survival of H. axyridis after feeding on four diets: injured wine grape berries, 25% sucrose solution, water, and a control containing no food or water. After being exposed to these diets for 6 days, live individuals were transferred to clean plastic Petri dishes, and held at 5 ± 1 °C in growth chambers throughout the winter. Survival was recorded every month. Adult lady beetles collected during the overwintering flight in mid-October had higher survival rates than beetles collected from soybean fields in mid-August. These results suggest that an adaptation period prior to diapause increases the chances of lady beetle survival over the winter. In addition, injured wine grape berries, sugar, and water decreased beetle mortality during the overwintering months. Our results also showed that under similar conditions, females have higher survival during the winter than males. The importance of sugar and water on winter survival may drive H. axyridis adults to vineyards for feeding on wine grapes. Finally, we tested if adults of H. axyridis and the European paper wasp, Polistes dominulus Christ (Hymenoptera: Vespidae), were able to break the grape skin. Harmonia axyridis adults and paper wasps were not able to cause the primary injury to berries of Frontenac grapes under laboratory conditions. These results suggest that control of paper wasps in vineyards may not affect H. axyridis aggregations, and that H. axyridis feeding on wine grapes depends on previous injury to grape berries.     

Susceptibility of a native and an exotic lady beetle (Coleoptera: Coccinellidae) to Beauveria bassiana

The exotic multicolored Asian lady beetle, Harmonia axyridis, became established and recently spread across much of North America and southern Canada. In a habitat now used by both the invading H. axyridis and a native lady beetle, Olla v-nigrum, we discovered that the native lady beetle was commonly infected by Beauveria bassiana; whereas, the exotic H. axyridis, was not. Laboratory assays revealed that B. bassiana isolates collected from naturally infected O. v-nigrum were pathogenic to adult O. v-nigrum but not to adult H. axyridis. In contrast, the GHA strain of B. bassiana was not significantly pathogenic to O. v-nigrum nor H. axyridis. Late-season field collections revealed significantly higher B. bassiana infection of O. v-nigrum than H. axyridis. Our results lead us to hypothesize that low susceptibility of H. axyridis to B. bassiana (found to infect O. v-nigrum) may provide an intraguild advantage to H. axyridis over O. v-nigrum; this may also occur with other species of native lady beetles and other endemic entomopathogens in different habitats and regions.     

Interference competition between ladybird beetle adults (Coleoptera: Coccinellidae): effects on growth and reproductive capacity

Cage experiments were used to determine the minimum number of Aphis fabae Scopoli that females of the Azorean native ladybird beetle Coccinella undecimpunctata L. require per day to achieve maximum fecundity and to assess the effects of interference competition from conspecific and heterospecific [Harmonia axyridis (Pallas)] adult ladybirds on its growth and reproduction. The number of A. fabae at which females of C. undecimpunctata ate most aphids, achieved maximum reproduction and maintained their body weight, was 200. The presence of H. axyridis adults, unlike the presence of C. undecimpunctata, significantly affected the reproductive numerical response of C. undecimpunctata even though the resource was not in short supply. The results suggest that interference competition with heterospecifics may adversely affect the reproductive capacity of C. undecimpunctata. Based on previous results and those reported here, we suggest that the introduction of H. axyridis could endanger the population abundance and/or result in the competitive displacement of C. undecimpunctata from the Azorean ecosystem.     

Mechanisms of prey finding in the aphidophagous ladybird beetle,Harmonia axyridis [Coleoptera: Coccinellidae]

The mechanism of prey finding in adultHarmonia axyridis was investigated by presenting beetles with small gauze or polyethylene bags containing either aphidinfested leaves or healthy leaves alone together with empty control bags. Beetles were attracted to bags by olfactory and visual cues suggesting the presence of aphids, including the odor of aphid-infested leaves, the odor of aphids, the odor of healthy leaves, and the sight of leaves. Particularly effective in prolonging beetles's stay on bags visited was the odor of aphid-infested leaves. It is suggested that adults ofH. axyridis use olfactory and visual cues to detect prey before actual contact occurs. Use of such cues seems more advantageous than random searching, as has been reported in many previous studies of coccinellid foraging.

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Résumé Le mécanisme de découverte de la proie chez l'adulte d'Harmonia axyridis est étudié en donnant aux Coccinelles de petits sacs en gaze ou en polyéthylène contenant soit des feuilles infestées de pucerons, soit des feuilles saines seules, avec des sacs vides comme témoins. Les coccinelles sont attirées vers les sacs par des indicateurs olfactifs ou visuels suggérant la présence de pucerons, incluant l'odeur des feuilles infestées de pucerons, l'odeur des pucerons, l'odeur des feuilles saines et la vue des feuilles. L'odeur des feuilles infestées de pucerons est particulièrement efficace en prolongeant le séjour des Coccinelles sur le sac visité. Il est suggéré que les adultes d'H. axyridis utilisent des indicateurs olfactifs et visuels pour détecter leur proie avant que s'établisse le véritable contact. L'emploi de tels indicateurs semble plus avantageux que la recherche au hasard, comme cela a été indiqué dans de nombreuses études antérieures sur la quête alimentaire des Coccinelles.

     

A natural flightless mutation in the ladybird, Harmonia axyridis

A homozygous flightless strain, obtained by selection from a laboratory population of Harmonia axyridis Pallas (Coleoptera, Coccinellidae), has been reared under controlled conditions since 1982 after sampling in China. The adults of this flightless strain have normal elytra and wings but drop almost vertically when they attempt to fly. The origin of this mutation, whether laboratory or natural, is discussed. As the mutation does not affect the fitness of the beetles, this flightless strain can be used in biological control. Releasing flightless adults rather than larvae should provide the potential for more continuous control of aphids by both larvae and adults.     

Pollen as an alternative food for Harmonia axyridis

The current study examines the potential of the multicoloured Asian lady beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) to use pollen as a food to sustain development and reproduction in the absence of insect prey. Three populations of H. axyridis were used in this study: a long-term laboratory population (since 1998) and a melanic and non-melanic population originating from field collected individuals in Belgium. The insects were allowed to develop and reproduce on frozen eggs of Ephestia kuehniella Zeller (Lepidoptera: Phycitidae), frozen moist bee pollen or an even mixture of the two. Females of the field population offered the mixed diet initiated oviposition sooner than those fed only E. kuehniella eggs, but other developmental and reproductive traits were similar on these diets. A diet of pollen alone allowed 35–48% of the larvae of the field population of H. axyridis to successfully reach adulthood. However, developmental time for these individuals was prolonged by 31–49% and adult body weight was reduced by 37–68%, compared to individuals offered the diets containing E. kuehniella eggs. When fed exclusively on pollen in their larval and adult life, about 40% of the adult females of either field population were able to produce a small number of viable eggs. The laboratory and field strains differed in their response to diet for a number of developmental and reproductive traits. The exploitation of pollen and other plant foods at times when insect prey is scarce, may offer a further competitive advantage to the non-indigenous coccinellid H. axyridis over native European predatory lady beetles that share the same niche and are less capable of using pollen as an alternative food.     

半自然农田边界与相邻农田步甲和蜘蛛的时空分布

分别于小麦、玉米收获前后,采用陷阱法调查了华北地区典型农业景观中具有不同植被结构的农田边界及其相邻农田中两类重要天敌类群步甲和蜘蛛的多样性.通过比较农田生境及相邻农田边界间两类天敌群落的时空分布格局及其与相邻半自然生境植被群落的相关关系,探讨半自然农田边界对两类天敌类群的保护作用.结果表明: 整个取样季节农田边界处蜘蛛的多度显著高于农田内部;而步甲多样性在农田与边界间无显著性差异,仅呈现不同的群落结构;作物收获后蜘蛛分科数在边界处的增加以及在农田的减少,显示了蜘蛛在农田和边界之间的迁移活动.边界植被结构对蜘蛛和步甲多样性有不同影响:边界较高的草本层盖度和较低的乔木层盖度有利于增加农田中某些步甲优势种的多样性;而较高的草本层盖度有利于增加皿蛛科蜘蛛的多样性.因此,半自然生境的存在可以通过天敌在农田和边界之间的迁移运动促进农田天敌多样性的维持;但不同类型半自然生境植被群落结构可能影响其对不同天敌群落多样性的维持和保护作用.为促进农业景观对天敌的保护作用,提高其害虫控制功能,需要深入了解不同天敌的生境需求及食物需求,精心设计有利于天敌多样性维持的半自然生境.     

Local and landscape determinants of pollen beetle abundance in overwintering habitats

• 1 The development of integrated pest management strategies requires that the semi‐natural habitats scattered across the landscape are taken into account. Particular determinants of insect pest abundance in overwintering habitats just before they migrate onto crops appear to be poorly known and of crucial importance for understanding patterns of crop colonization and pest population dynamics at the landscape scale.
• 2 The emergence of pollen beetle Meligethes aeneus F. was studied in grassland, woodland edge and woodland interior over a 3‐year survey in France using macro‐emergence traps. A suite of variables at the local and the landscape scale was assessed for each trap, aiming to identify potential relevant habitat indicators. The effects of habitat characteristics were evaluated using partial least square regressions.
• 3 It was found that M. aeneus can overwinter in all types of habitat but that particular habitat characteristics at the local and landscape scales may explain their abundance in overwintering sites more than the types of habitat: relative altitude, litter thickness, soil moisture and proximity to the previous year's oilseed rape fields appear to be positively correlated with abundance of adults over the 3 years.
• 4 Hence, the abundance of emerged pollen beetles depends on both the landscape configuration of the previous year's oilseed rape fields around overwintering sites and local habitat characteristics. Landscape configuration may determine population flow towards overwintering sites in the late summer, and local habitat characteristics may influence survival rates during the winter. The findings of the present study provide valuable insight into the role of semi‐natural habitats as a source of pests, patterns of crop colonization in the spring, and the influence of landscape on pollen beetle abundance.

     

Predicted Impact of an Exotic Generalist Predator on Monarch Butterfly (Lepidoptera: Nymphalidae) Populations: A Quantitative Risk Assessment

The multicolored Asian lady beetle, Harmonia axyridis (Pallas), was recently identified as a potential hazard to monarch butterflies, Danaus plexippus (L.). A quantitative risk assessment for the potential impact of H. axyridis on D. plexippus in Minnesota corn and soybean fields was developed using risk analysis software. This assessment considered a potential worst-case scenario for the impact of H. axyridis on D. plexippus. Habitat-specific recruitment of D. plexippus eggs was determined empirically. Subsequently, simulated abundance of D. plexippus in each habitat was reduced by two classes of stage-specific mortality: predation by H. axyridis and causes other than H. axyridis. Predation was modeled as a function of D. plexippus exposure to H. axyridis, and predation rate of D. plexippus by H. axyridis. Exposure and subsequent risk varied considerably by habitat, with a low risk of H. axyridis adversely affecting D. plexippus populations developing in corn fields, but a moderate to high risk in soybean fields. Predicted rates of D. plexippus mortality attributable to H. axyridis were greater in soybean compared to corn fields, possibly due to the numerical response of H. axyridis to soybean aphid, Aphis glycines Matsumura. This study demonstrates that H. axyridis has the potential to have a strong adverse impact on D. plexippus populations. However, the likelihood of occurrence for this worst-case scenario remains uncertain. To evaluate the landscape-level risk of H. axyridis impacting D. plexippus, further data on recruitment of D. plexippus in other habitats and exposure estimates specific to additional habitats are needed.     

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.     

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.     

Ecology and biological control application of multicoloured Asian ladybird, Harmonia axyridis: A review

The ecology of and biological control by multicoloured Asian ladybird beetle, Harmonia axyridis (Pallas) are reviewed. Our emphasis is on assembling and interpreting information on general characteristics, invasion and establishment, sexual activity, foraging and predation, development, survival and reproduction, predator-predator interactions, natural enemies, biocontrol, non-target effects and status of H. axyridis as a pest of fruits. Colonization of H. axyridis for aphid biocontrol in the USA have been successful in terms of its establishment, but its abundance is turning out to be a nuisance to humans. Its harmful non-target impact on beneficial organisms, humans and native species is becoming a debatable issue. The question on its present position, whether it is a biocontrol agent or pest, is a critical issue and discussed. Inferences from the empirical data are made and new avenues for future research are suggested.     

Effect of resource gradient on age and size at maturity and their influence on early‐life fecundity in the predatory Asian lady beetle,Harmonia axyridis

Variation in food availability impacts the performance of insects in terms of their size and age to maturity and fecundity. Age at maturity determines how quickly individuals in a population can start to reproduce and how much they can reproduce. Results from studies on various insect species show that food availability influences the size and fecundity of adult females. It is predicted that under poor growth conditions, variation in size is low, but variation in age at maturity is considerable. This prediction was examined in a widely distributed lady beetle species, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), a predator of aphids and coccids. Using a food gradient from low to high aphid prey density, performance of females that were reared on excess food was recorded for pre‐reproductive duration, size at reproductive maturity, number of aphids consumed, and fecundity in the first 10 days of their reproductive period. Results suggested that female H. axyridis that were reared on surplus food when kept at low prey density (poor growth condition) took, on average, three times longer to attain maturity and produced, on average, 14 times fewer eggs than females that were also reared on surplus food, but kept at high prey density (good growth condition). Females performed best at a prey density of 30 aphids per female per 150 cm². Results suggested that the current food availability significantly influenced the age and size of females at maturity and their fecundity. Age and size at maturity of female lady beetles showed non‐linear responses to prey density as well as the occurrence of a minimum size of females, below which H. axyridis females fail to mature. The steep slope recorded at lower prey densities suggests relatively high variation in age at maturity but low variation in size.     

Role of visual and olfactory cues from agricultural hedgerows in the orientation behavior of multicolored Asian lady beetle (Coleoptera: Coccinellidae)

Harmonia axyridis Pallas is an introduced lady beetle common in eastern North American agroecosystems. Two-choice behavioral bioassays were performed to determine whether visual and olfactory stimuli from prey and host habitats could elicit taxis in wild-collected H. axyridis adults and whether beetles exhibit a preference among stimuli. Soybean aphid (Aphis glycines Matsumura) spends much of the year in agricultural hedgerows residing on buckthorn (Rhamnus cathartica L), and H. axyridis is frequently observed feeding on aphids in this habitat. Olfactory bioassays were performed in a Y-tube olfactometer and tested the response of beetles to the odor of buckthorn leaves, apple leaves (Malus domestica Borkh.), and buckthorn leaves both naturally and artificially infested with A. glycines. No differences were observed between the numbers of beetles moving toward the odor of buckthorn artificially infested with A. glycines and uninfested buckthorn, but more beetles preferred naturally infested buckthorn over uninfested buckthorn. Visual bioassays were performed in an acrylic tube arena,and tested beetle response to silhouettes and to apple and buckhorn leaves. Beetles were significantly more likely to choose silhouettes over blank space in visual trials. Significantly more beetles moved toward buckthorn leaves than blank space, but beetles did not discern between apple and buckthorn until olfactory cues were also included. This study lays the foundation for future work examining the response of H. axyridis to visual and olfactory cues in Ontario agroecosystems, which could help enhance effectiveness of H. axyridis as a biological control and mitigate its impacts as a pest species.     

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.     

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.     

Intraguild predation involving Harmonia axyridis: a review of current knowledge and future perspectives

As an effective generalist predator of aphids and other hemipteran pests H. axyridis has been a successful biological control agent. However, the very functional traits that have contributed to its success in this regard also implicate it as an intraguild predator that poses a significant risk not only to the diversity of other natural enemies of Hemiptera (and their associated ecosystem services), but to biodiversity more widely. In this paper we will specifically review the existing data on intraguild predation involving H. axyridis, and consider the strength and symmetry of such interactions both within its native guild and within exotic guilds where it has established as an invasive alien. We will use these studies to interpret the observed population declines in predator diversity in the field, predict species at risk in regions not yet invaded and consider implications for resulting ecosystem services. We will also indicate gaps in our knowledge that require further study in order to identify opportunities for mitigation.