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.     

Spatial refuge from intraguild predation: implications for prey suppression and trophic cascades

The ability of predators to elicit a trophic cascade with positive impacts on primary productivity may depend on the complexity of the habitat where the players interact. In structurally-simple habitats, trophic interactions among predators, such as intraguild predation, can diminish the cascading effects of a predator community on herbivore suppression and plant biomass. However, complex habitats may provide a spatial refuge for predators from intraguild predation, enhance the collective ability of multiple predator species to limit herbivore populations, and thus increase the overall strength of a trophic cascade on plant productivity. Using the community of terrestrial arthropods inhabiting Atlantic coastal salt marshes, this study examined the impact of predation by an assemblage of predators containing Pardosa wolf spiders, Grammonota web-building spiders, and Tytthus mirid bugs on herbivore populations (Prokelisia planthoppers) and on the biomass of Spartina cordgrass in simple (thatch-free) and complex (thatch-rich) vegetation. We found that complex-structured habitats enhanced planthopper suppression by the predator assemblage because habitats with thatch provided a refuge for predators from intraguild predation including cannibalism. The ultimate result of reduced antagonistic interactions among predator species and increased prey suppression was enhanced conductance of predator effects through the food web to positively impact primary producers. Behavioral observations in the laboratory confirmed that intraguild predation occurred in the simple, thatch-free habitat, and that the encounter and capture rates of intraguild prey by intraguild predators was diminished in the presence of thatch. On the other hand, there was no effect of thatch on the encounter and capture rates of herbivores by predators. The differential impact of thatch on the susceptibility of intraguild and herbivorous prey resulted in enhanced top-down effects in the thatch-rich habitat. Therefore, changes in habitat complexity can enhance trophic cascades by predator communities and positively impact productivity by moderating negative interactions among predators.     

Life history characteristics of Orius insidiosus (Say) fed diets of soybean aphid, Aphis glycines Matsumura and soybean thrips, Neohydatothrips variabilis (Beach)

Field studies in soybeans have demonstrated that the endemic predator, Orius insidiosus (Say), is an important natural enemy of the soybean aphid, Aphis glycines Matsumura. Soybean thrips, Neohydatothrips variabilis (Beach), serve as an important prey resource for O. insidiosus in soybeans and may be important in sustaining O. insidiosus populations before the arrival of soybean aphid. Because soybean aphid is new to the US soybean system, the effects of a mixed diet of soybean aphid and soybean thrips on O. insidiosus life history is not known. We measured the survival, development, and reproduction of O. insidiosus when fed soybean thrips, and a mixed prey diet of soybean aphids and soybean thrips, and compared these results to a previous study of O. insidiosus life history fed soybean aphid alone. Nymphal development to adulthood (15.9 days) and fecundity (68.8 eggs per female) was improved for O. insidiosus fed ad libitum soybean thrips daily compared to O. insidiosus fed ad libitum soybean aphids daily. The contribution of alternative prey to O. insidiosus life history characteristics can be complex depending on the amount and quality of a particular prey item. At low levels of prey, the addition of prey appears to enhance O. insidiosus survival, development, and fecundity. However, as predators are fed more often, the predator’s response depends on the type of prey that predominates in the mixed prey diet. We discuss soybean thrips impact on O. insidiosus population ecology and soybean aphid dynamics.     

The role of natural enemy guilds in Aphis glycines suppression

Generalist natural enemy guilds are increasingly recognized as important sources of mortality for invasive agricultural pests. However, the net contribution of different species to pest suppression is conditioned by their biology and interspecific interactions. The soybean aphid, Aphis glycines (Hemiptera: Aphididae), is widely attacked by generalist predators, but the relative impacts of different natural enemy guilds remains poorly understood. Moreover, low levels of A. glycines parasitism suggest that resident parasitoids may be limited through intraguild predation. During 2004 and 2005, we conducted field experiments to test the impact of different guilds of natural enemies on A. glycines. We contrasted aphid abundance on field cages with ambient levels of small predators (primarily Orius insidiosus) and parasitoids (primarily Braconidae), sham cages and open controls exposed to large predators (primarily coccinellids), and cages excluding all natural enemies. We observed strong aphid suppression (86- to 36-fold reduction) in treatments exposed to coccinellids, but only minor reduction due to small predators and parasitoids, with aphids reaching rapidly economic injury levels when coccinellids were excluded. Three species of resident parasitoids were found attacking A. glycines at very low levels (<1% parasitism), with no evidence that intraguild predation by coccinellids attenuated parasitoid impacts. At the plant level, coccinellid impacts resulted in a trophic cascade that restored soybean biomass and yield, whereas small natural enemies provided only minor protection against yield loss. Our results indicate that within the assemblage of A. glycines natural enemies in Michigan, coccinellids are critical to maintain aphids below economic injury levels.     

Direct effects of soybean varietal selection and Aphis glycines-resistant soybeans on natural enemies

The direct effects of three soybean parentages, each represented by an Aphis glycines-resistant and susceptible isoline, on the fitness and performance of two key predators (Orius insidiosus and Harmonia axyridis) were evaluated in the laboratory. Predators were reared from hatch through adulthood in Petri dishes with cut trifoliolate leaves of the designated soybean variety, using eggs of Ephestia kuehniella as surrogate prey to eliminate prey-mediated effects of the host plant. Preimaginal survival and development, sex ratio, adult longevity, fecundity, and size were compared among treatments and a no-plant control. An additional experiment compared life-history parameters of predators caged with soybean versus Ipomoea hederacea (ivyleaf morning glory). Aphid resistance reduced the adult longevity of H. axyridis, but O. insidiosus was unaffected by resistance traits. However, adult O. insidiosus lived longer on soybeans with Group C base genetics than the other soybean varieties. Other parameters were not affected by soybean base genetics or resistance, but both predators generally performed worse on soybean than on I. hederacea or no-plant controls. The results suggest that soybean varietal selection, particularly with respect to A. glycines-resistance, may directly affect biological control agents. Also, implications of the generally poor suitability of soybean for natural enemies are discussed within the context of current crop production practices. Handling editor: Michael Smith     

The effect of flowering calendula and cuphea plants on Orius insidiosus survival and predation of Aphis glycines

Flowering oilseed crops have the potential to diversify agroecosystems currently dominated by corn and soybeans and improve the provision of ecosystem services such as pest control. Nectar and pollen feeding may increase natural enemy fitness and searching behaviour, increasing their survival and prey consumption rates. The soybean aphid (Aphis glycines Matsumura; Hemiptera: Aphididae) is a particularly widespread and costly agricultural pest. In this study, we evaluate the effects of two flowering oilseed crops, cuphea and calendula, on the survival of the insidious flower bug (Orius insidiosus Say; Hemiptera: Anthocoridae) and its consumption levels of A. glycines placed on soybean plants. We also evaluated the survival of O. insidiosus when placed on glandular and non-glandular cuphea varieties. The amount of A. glycines that remained unconsumed by O. insidiosus did not differ among treatments. Because mortality levels of O. insidiosus were higher on glandular compared to non-glandular cuphea plants, glandular trichomes, or plant hairs, may play a role in impeding movement and prey consumption by O. insidious.     

Temporal relationships between the generalist predator,Orius insidiosus,and its two major prey in soybean

The generalist predator, Orius insidiosus (Say) is an important early-season predator of the soybean aphid, Aphis glycines Matsumura, a newly invasive pest of major concern in soybean crop management. We conducted a 3 year, multiple field study to characterize the dynamic relationships between the predator, the pest, and alternative prey in soybean. Using field sampling data, we showed that thrips were the only alternative prey to be well-established in fields prior to O. insidiosus arrival and were likely to promote predator colonization of soybean fields prior to the arrival of soybean aphid. The predator displayed a reproductive numerical response to thrips in one of the 3 years and a primarily aggregative response in another year. The predator did not respond numerically to soybean aphid in the majority of fields. Experimental manipulations of thrips populations in field plots temporarily reduced thrips densities but had a minimal effect on O. insidiosus densities, suggesting that the predator is resilient against temporary reductions in a major resource. In the 2 years O. insidiosus populations were well-established in fields prior to soybean aphid arrival, soybean aphid remained at low levels throughout the season. In the year soybean aphid arrived early with respect to the growing season and before O. insidiosus populations were established, soybean aphid reached outbreak levels in all fields. Future research efforts on the factors determining soybean aphid population dynamics need to address the relative importance of early-season soybean aphid colonization and generalist predator population dynamics on the potential for soybean aphid population outbreaks.     

Intraguild Interactions Between the Predatory Mites Neoseiulus californicus and Phytoseiulus persimilis

Species at the same trophic level may interact through competition for food, but can also interact through intraguild predation. Intraguild predation is widespread at the second and third trophic level and the effects may cascade down to the plant level. The effects of intraguild predation can be modified by antipredator behaviour in the intraguild prey. We studied intraguild predation and antipredator behaviour in two species of predatory mite, Neoseiulus californicus and Phytoseiulus persimilis, which are both used for control of the two-spotted spider mite in greenhouse and outdoor crops. Using a Y-tube olfactometer, we assessed in particular whether each of the two predators avoids odours emanating from prey patches occupied by the heterospecific predator. Furthermore, we measured the occurrence and rate of intraguild predation of different developmental stages of P. persimilis and N. californicus on bean leaves in absence or in presence of the shared prey. Neither of the two predator species avoided prey patches with the heterospecific competitor, both when inexperienced with the other predator and when experienced with prey patches occupied by the heterospecific predator. Intraguild experiments showed that N. californicus is a potential intraguild predator of P. persimilis. However, P. persimilis did not suffer much from intraguild predation as long as the shared prey was present. This is probably because N. californicus prefers to feed on two-spotted spider mites rather than on its intraguild prey.     

Role of aphid predator guild in controlling spirea aphid populations on apple in West Virginia,USA

Spirea aphid populations and their predators were studied on apple to identify predators of importance in controlling aphid populations. Methods included random and non-random sampling from apple orchards in West Virginia, USA, sentinel aphid colonies, laboratory feeding studies, and predator exclusion studies. Aphidoletes aphidimyza (Diptera: Cecidomyiidae), chrysopids (Neuroptera: Chrysopidae), Harmonia axyridis (Coleoptera: Coccinellidae), and Orius insidiosus (Hemiptera: Anthocoridae) were the most abundant predators associated with spirea aphid colonies on apple. Parasitoids were all but absent in the study. Abundance of all predators was density dependent with greater responses to aphid populations at the orchard scale than to tree or individual colony scales. A. aphidimyza, O. insidiosus, chrysopids, and syrphids (Diptera) had the greatest degree of density dependence on aphid populations, and spiders showed inverse density dependence. Exclusion of predators with both cages and insecticides produced significantly higher aphid populations. Because of high abundance, good synchrony with aphid populations, and high impact per individual, H. axyridis adults were the most important spirea aphid predator on apple.     

Life history characteristics of Orius insidiosus (Say) fed Aphis glycines Matsumura

The soybean aphid, Aphis glycines Matsumura, is a new invasive pest of soybeans throughout most of the soybean production areas of North America. Field studies have demonstrated that the indigenous predator, Orius insidiosus (Say), is an important natural enemy of the soybean aphid early the soybean crop season. Because soybean aphid is newly introduced into North America, the life history characteristics of predators fed this aphid are not known. In laboratory assays, we measured the survival, development, longevity and reproduction of O. insidiosus fed 1, 3, 6 or 12 seconds to third instars of soybean aphid. O. insidiosus nymphal development decreased from 34.0 to 21.4 days as the number of soybean aphid nymphs provided increased from 1 to 6 aphid nymphs daily. Stage-specific mortality was highest at 68% for first instar O. insidiosus nymphs fed 1 soybean aphid nymph per day. Adult longevity (43.9 days) and fecundity (49.7 eggs per female) was highest for O. insidiosus fed 6 soybean aphid nymphs daily, but longevity (23.5 days) and fecundity (10.1 eggs per female) declined for adults fed 1 soybean aphid nymph daily. The intrinsic rate of increase of O. insidiosus ranged from 0.048 to 0.133. Compared to other prey species, soybean aphid is an adequate prey item for O. insidiosus. Our results suggest that O. insidiosus will be most effective in suppressing soybean aphid population growth in the initial phase of the aphid’s colonization of soybeans.     

Invasion of the coccinellid community associated with a tropical annual agroecosystem

1. Detailed understanding of the mechanisms enabling or limiting the impacts of invasive generalist predators is needed. Harmonia axyridis is an invasive generalist coccinellid predator that may have destabilised coccinellid communities worldwide and is an excellent candidate for investigating invasion dynamics.
2. We evaluated four hypotheses: (1) Nine years after being detected in Central Brazil, Ha. axyridis has dominated the coccinellid community. This is facilitated by (2) its broader aphid prey range than the other aphidophagous coccinellids, (3) its superiority as an asymmetrical intraguild predator, and (4) the invasibility of the present coccinellid community.
3. We sampled the invertebrate communities associated with six organic vegetable farms in Brazil during 2017 and 2018, conducted a feeding trial to measure prey niche breadth and overlap, and estimated intra- and interspecific interaction strengths corresponding to first-order Lotka-Volterra parameters to evaluate the strength of intraguild predation and create a community matrix.
4. We found (1) Ha. axyridis comprised ≤8.3% of the coccinellid community. (2) Hi. convergens had the broadest prey niche and dominated the prey niche of Ha. axyridis. (3) We could not determine from the population data if Ha. axyridis was the dominant intraguild predator because its density was too low and constant. (4) The community matrix indicated that the present-day coccinellid community was stable.
5. We conclude Ha. axyridis has not become invasive in Central Brazil, in part because it does not have the broadest prey niche breadth and the present coccinellid community is stable to the present perturbation of Ha. axyridis.

     

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.     

Predator diversity and the functioning of ecosystems: the role of intraguild predation in dampening trophic cascades

Single trophic‐level studies of the relationship between biodiversity and ecosystem functioning highlight the importance of mechanisms such as resource partitioning, facilitation, and sampling effect. In a multi‐trophic context, trophic interactions such as intraguild predation may also be an important mediator of this relationship. Using a salt‐marsh food web, we investigated the interactive effects of predator species richness (one to three species) and trophic composition (strict predators, intraguild predators, or a mixture of the two) on ecosystem functions such as prey suppression and primary production via trophic cascades. We found that the trophic composition of the predator assemblage determined the impact of increasing predator species richness on the occurrence of trophic cascades. In addition, increasing the proportion of intraguild predator species present diminished herbivore suppression and reduced primary productivity. Therefore, trophic composition of the predator assemblage can play an important role in determining the nature of the relationship between predator diversity and ecosystem function.     

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.     

Effect of pollen supplement on intraguild predatory interactions between two omnivores: The importance of spatial dynamics

Arthropods often engage in complex trophic interactions such as intraguild predation (IGP), true omnivory (i.e., feeding on plants and prey), and apparent competition. Theoretical treatments of the effects of such interactions on herbivore populations have been concerned almost entirely with equilibrium conditions. Yet these interactions are common in non-equilibrium settings such as agroecosystems, where they are likely to have a strong influence on pest populations. We therefore tested short-term effects of IGP and food supplementation on interactions between two predators (the phytoseiid mite Neoseiulus cucumeris and the anthocorid bug Orius laevigatus) and their shared prey, Frankliniella occidentalis, on strawberry plants. All three consumers feed on strawberry pollen, both mites and bugs prey on thrips, and the bug also feeds on the mites (IGP). Strong IGP on mites (IG prey) by the bugs (IG predator) was recorded in structurally-simple arenas. In a more complex setting (whole-plants), however, the intensity of IGP differed among plant structures. Likewise, pollen supplementation reduced both IGP and predation on thrips in a structurally simple setting. In the whole-plant experiment, IGP was more intense on pollen-bearing than pollen-free flowers. The study illustrated how spatial dynamics, generated when consumers track food sources differently in the habitat and possibly when herbivorous and IG prey alter their distribution to escape predation, led to site-specific configuration of interacting populations. The intensity of resulting trophic interactions was weakened by food supplementation and by increased complexity of the habitat.     

Plant quality effects on intraguild predation between Orius laevigatus and Aphidoletes aphidimyza

To understand the influence of plant quality on intraguild predation and consequently on the suppression of a shared prey population as well as on plant yield, the interactions between Aphis gossypii Glover (Hemiptera: Aphididae) (shared prey), Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae) (intermediate predator), and Orius laevigatus Fieber (Hemiptera: Anthocoridae) (top predator) were investigated in 25‐day experiments on cucumber, Cucumis sativus L. (Cucurbitaceae) at various N fertilization levels (90, 150, and 190 p.p.m.) in microcosm set‐ups under greenhouse conditions. The final aphid population size was significantly affected by an interactive effect of N fertilization and predator application. Regardless of the N fertilization levels, O. laevigatus alone was more effective in aphid suppression than A. aphidimyza alone. In addition, the risk for aphids of being predated upon by both predators together was significantly reduced in the low and medium‐N fertilization levels, whereas it was additive in the high‐N fertilization treatment. The A. aphidimyza population was suppressed by O. laevigatus in both the 90 and 150 p.p.m. N treatments. However, there was no intraguild predation of O. laevigatus on A. aphidimyza at the 190 p.p.m. N level. Total plant yield depended on predator treatments and N fertilization levels, with the highest yield produced at the 150 p.p.m. N fertilization level in treatments with either O. laevigatus alone or with both predators together. Our results demonstrate that the weak asymmetric intraguild predation among A. aphidimyza and O. laevigatus does not influence the ability of both predators together to diminish bottom‐up effects on aphid populations and the yield losses associated with aphid infestations.     

Intraguild interactions among generalist predator functional groups drive impact on herbivore and decomposer prey

Different functional groups of generalist predators may complement each other in controlling prey populations; but intraguild interactions, common among generalist predators, may also reduce the strength of top–down control. In natural communities greater alterations to ecosystem function are expected if a whole functional group declines in abundance or is lost. Therefore studying functional group diversity is important for predicting effects of predator loss. We studied the top–down impact of web‐building spiders, hunting spiders and ants, which are highly abundant generalist predators in most terrestrial ecosystems, on prey from the herbivore and decomposer system of a grassland food web. The density of the three predator groups was manipulated by continuous removal in a three‐factorial designed field experiment, which was carried out for two years. We found no positive effect of increasing predator functional group richness on prey control. However there was evidence for strong composition effects between the functional groups. The presence of ants in predator assemblages reduced the prey suppression through mostly trait‐mediated intraguild interactions, while hunting and web‐building spiders contributed additively to prey suppression and reduced the density of herbivore and decomposer prey by 50–60%. A trophic cascade on plant biomass triggered by web‐builders and hunting spiders was diminished at levels of higher predator group diversity. In conclusion, our experiments showed that intraguild interactions strongly influence the strength of top–down control by generalist predators. Among spiders there was evidence for a positive relation between functional group richness and prey suppression but the overall outcome strongly depended on the occurrence of interference, driven by trait‐mediated indirect interactions.     

Predation of cotton leafworm first instar larvae,Alabama argillacea [Lep.: Noctuidae]

Natural predation first instar larvae of the cotton leafworm (CLW)A. argillacea was studied in cotton fields in Jaboticabal, Sao Paulo State, Brazil, during 1986. The presence of naturally occurring arthropod predators showed a first instar larvae predation rate of 78.6 and 88.9% after 24 h and 48 h of exposure, respectively. A predator prey ratio of 1∶1 (1 CLW key predator per 1 prey/plant) maintained a level of no more than 1 CLW small larvae per plant. The most evident arthropod predators in the studied fields were: beetles (Coleoptera: Coccinellidae), antsPheidole sp. andConomyrma sp.;Dermaptera Doru lineare (Eschs);Hemiptera Geocoris sp., andOrius insidiosus Say; and the spidersTheridion volubile, Chrysso pulcherrima, Misumenops sp.,Chiracanthium sp., andOxyopes salticus Hentz.      

Reaping benefits from an invasive species: role of <Emphasis Type="Italic">Harmonia axyridis</Emphasis> in natural biological control of <Emphasis Type="Italic">Aphis glycines</Emphasis> in North America

Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is an invasive species present in numerous agroecosystems in North America. Despite adverse impacts as a threat to native biodiversity, a nuisance household invader and a pest in fruit production, H. axyridis also plays a beneficial role as a major component of assemblages of generalist predators in several agricultural crops. Here, we review the role of H. axyridis as a natural enemy of Aphis glycines Matsumura (Hemiptera: Aphididae), an invasive pest of soybean, Glycine max (L.) Merrill (Fabales: Fabaceae), in North America. Harmonia axyridis is often the most abundant predator species attacking A. glycines in soybean agroecosystems. This predator has the potential to both prevent and suppress A. glycines outbreaks. Further studies are needed to fully understand and utilize the potential of H. axyridis as a natural enemy in the management of A. glycines and other agricultural pests in agroecosystems worldwide.     

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.