Alfalfa fields promote high reproductive rate of an invasive predatory lady beetle

Invasive insect species often may attain high fecundity in agricultural habitats, thereby contributing to their establishment in new geographic regions and their displacement of similar native species. Such may be true for predatory lady beetles (Coleoptera: Coccinellidae) that have been introduced to North America in recent decades, raising concerns of adverse impact on native lady beetles. In northern Utah, Coccinella septempunctata L. first appeared in 1991, and is now predominant among lady beetles especially in alfalfa fields. We assessed the suitability of alfalfa fields as breeding habitat for females of C. septempunctata and the native, similarly sized Coccinella transversoguttata richardsoni Brown. The timing and amount of egg production differed significantly between C. septempunctata and C. transversoguttata as populations of aphids increased through spring and early summer. Reproduction by both species conformed to the egg window hypothesis, with populations of the predators producing most eggs before aphid numbers peaked. But consistently among fields and years, females of C. septempunctata produced more eggs, and did so earlier in the spring, than C. transversoguttata females even at low prey density. Furthermore, C. septempunctata females were more successful than females of C. transversoguttata in approaching their maximum body weights and reproductive output as measured in the laboratory under ideal conditions. The strong reproductive success of C. septempunctata may contribute to its displacement of C. transversoguttata in irrigated alfalfa in the generally arid Intermountain West of North America and to its establishment as an abundant species in this region of North America.     

Effects of a microsporidium from the convergent lady beetle, Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae), on three non-target coccinellids

A microsporidium from Hippodamia convergens was transmitted horizontally to three non-target coccinellid hosts (Adalia bipunctata L., Coccinella septempunctata L. and Harmonia axyridis Pallas) under laboratory conditions. For all species examined, microsporidia-infected larvae took significantly longer to develop than did uninfected larvae but the microsporidium had no effect on larval mortality. Adult sex ratios of uninfected and microsporidia-infected adults were about 1:1 (♀:♂) and did not differ significantly. At the end of a 90-day trial, microsporidia-infected H. convergens produced significantly fewer eggs and did not live as long as uninfected individuals. Differences in fecundity and longevity were not observed for the three non-target coccinellids that were examined. Mean spore counts from smear preparations of microsporidia-infected A. bipunctata did not differ significantly from H. convergens, suggesting that A. bipunctata (a native coccinellid) is a suitable host for the microsporidium but infection was lighter in C. septempunctata and H. axyridis (introduced species). Vertical transmission of the pathogen was observed during the 90-day trial by examining eggs and larvae that were produced by microsporidia-infected adults. For all species examined, 100% vertical transmission of the pathogen was eventually observed. Three eugregarines were found in two adult A. bipunctata: Gregarine A trophozoites are similar in size to those of Gregarina katherina Watson (described earlier from Coccinella spp.), Gregarine B trophozoites are similar in size to those of Gregarine A but are morphology distinct, and Gregarine C trophozoites are similar in size to G. barbarara Watson (described earlier from A. bipunctata).     

Changes in A Lady Beetle Community Following the Establishment of Three Alien Species

A number of recent studies indicated that establishment of exotic lady beetles (Coleoptera: Coccinellidae) may have adverse affects on native lady beetle species. In the present study, we analyzed changes in coccinellid community inhabiting potato crops in northern Maine over the past 31 years. Prior to 1980, lady beetle communities were comprised almost exclusively of the two native species, Coccinella transversoguttata Brown and Hippodamia tredecimpunctata(Say). Starting 1980, an exotic species Coccinella septempunctata L. became permanently established in potato crops and quickly started to dominate lady beetle community. Two other exotic species, Harmonia axyridis(Pallas) and Propylea quatordecimpunctata(L.) became prominent members of the lady beetle community in 1995 and 1996. Invasion by exotic species was followed by a significant decline in the abundance of C. transversoguttata and H. tredecimpunctata, and a significant increase in the overall diversity of lady beetle community. The abundance of aphid prey was substantially reduced after the establishment of H. axyridis. The observed trends demonstrate the profound effects that exotic natural enemies may have on target and non-target native species, and highlight the importance of their thorough evaluation before initiating biological control programs.     

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.     

Diversity and abundance of coccinellids (Coleoptera: Coccinellidae) on trees in parks and tree rows of Belgrade

Harmonia axyridis is an invasive coccinellid species that was first recorded in Serbia in 2008. In order to establish whether after its arrival it became the dominant coccinellid species, we investigated the diversity and abundance of coccinelids on trees in parks and tree rows of Belgrade during 2015 and 2016. Thirteen coccinellid species were recorded in these investigations. Frequently occurring among them were Adalia bipunctata, A. decempunctata, Coccinella septempunctata, Exochomus quadripustulatus, Harmonia axyridis, H. quadripunctata, Oenopia conglobata, and Popylea quatuordecimpunctata. All of them had different dynamics of appearance during the vegetation. As a result of this, the values of their dominance in the coccinellid community constantly changed. However, only in the cases of H. axyridis, O. conglobata, and C. septempunctata were those values high enough for us to be able to say that they were dominant in terms of abundance during a certain period. Although the amounts of summer precipitation in Serbia were very different during 2015 and 2016, the trends of changes in the diversity of coccinellids throughout the growing season in these two years were similar.     

Effects of Aphid Prey on Larval Development and Mortality of Adalia bipunctata and Coccinella septempunctata (Coleoptera: Coccinellidae)

Developmental time and mortality rate of Adalia bipunctata (L.) and Coccinella septempunctata L. (Coleoptera: Coccinellidae) were determined when feeding on five aphid species. Metopolophium dirhodum (Walker), Sitobion avenae (F.), Rhopalosiphum padi (L.), Hyalopterus pruni (Geoffr.) and Myzus cerasi F. (Homoptera: Aphididae) are widespread in Tekirda?, Turkey. Tests were carried out in a controlled environmental chamber (25±1°C temperature, 65±5% relative humidity and 16 h light:8 h dark period). Developmental times for A. bipunctata and C. septempunctata larvae varied significantly depending on species of aphid prey (P<0.05). Development time (±S.E.) varied from 17.50±0.84 to 20.83±1.60 days for C. septempunctata and 16.7±0.76 to 20.7±1.03 days for A. bipunctata. Mortality of A. bipunctata (50%) and C. septempunctata (63%) were highest on H. pruni.     

Species abundance patterns of coccinellid communities associated with olive,chestnut and almond crops in north‐eastern Portugal

• 1 The patterns of abundance of coccinellid species associated to the main agricultural tree crops of north‐eastern Portugal namely olive, chestnut and almond were studied.
• 2 During three to four crop seasons, eight olive, five chestnut and one almond groves were sampled. In each grove, five samples were collected from 10 randomly selected trees using the beating technique and the coccinellids were counted and identified to species. Principal component analysis was used to establish associations among crop and coccinellid species.
• 3 The mean species richness was higher in chestnut, with 15 ± 3.81 species/grove, followed by olive and almond, with 13 ± 2.76 and 10 ± 2.97 species/grove, respectively. Scymnus mediterraneus was the most abundant species in olive and almond, whereas Scymnus interruptus was dominant in chestnut. Brumus quadripustulatus, Chilocorus bipustulatus, Scymnus subvillosus, S. mediterraneus and Rhyzobius chrysomeloides were associated with olive, whereas S. interruptus, Coccinella septempunctata and Adalia decempunctata were associated with chestnut and Hippodamia variegata, Oenopia conglobata and Adalia bipunctata with almond. Both Stethorus punctillum and Scymnus apetzi species were similarly associated with chestnut and almond.
• 4 The differences in coccinellid communities could have been related to the kind of prey item present in the different trees. This knowledge can be used to develop integrated pest management programmes that encourage greater natural enemy biodiversity in agroecosystems.

     

Toxicity of plant essential oil vapours to aphid pests and their coccinellid predators

The comparative toxicity of five essential oil vapours was tested against four aphid species, the black bean aphid Aphis fabae, the pea aphid Acyrthosiphon pisum, the chrysanthemum aphid Macrosiphoniella sanborni, the green peach aphid Myzus persicae and on two of the most common coccinellid predators, the seven-spotted ladybird Coccinella septempunctata and the two-spotted ladybird Adalia bipunctata. All essential oils were highly toxic to the aphid species tested with LC₅₀ and LC₉₉ values ranging between 0.17 and 1.92 and 0.44 and 4.83 µL/L air, respectively, depending on the aphid species and on the essential oil. Coccinellid predators were also highly susceptible to the essential oil vapours and the selective toxicity ratio varied depending on aphid species, coccinellid predator and essential oil. The possibilities for the utililization of essential oils as aphicides, especially in IPM programmes in glasshouses are discussed with regard to the present findings.     

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.     

Assessment of patch quality by ladybirds: role of larval tracks

Gravid females of the two-spot ladybird, Adalia bipunctata (L.), were deterred from ovipositing when kept in petri dishes that had previously contained conspecific larvae but not conspecific adults, or the larvae of another two species of ladybird, Adalia decempunctata (L.) and Coccinella septempunctata L. The deterrent effect was density dependent and mediated via a chloroform-soluble contact pheromone present in the larval tracks. Similarly, gravid females of C. septempunctata were deterred from ovipositing by conspecific larval tracks and chloroform extracts of these tracks, but not by the tracks or extracts of tracks of A. bipunctata larvae. That is, in ladybirds the larvae produce a species-specific oviposition-deterring pheromone. In the field, the incidence of egg cannibalism in ladybirds increases very rapidly with the density of conspecific eggs or larvae per unit area. Thus, in responding to the species specific oviposition deterring pheromone female ladybirds reduce the risk of their eggs being eaten and spread their offspring more equally between patches. Received: 14 March 1997 / Accepted: 26 August 1997     

The decline of native coccinellids (Coleoptera: Coccinellidae) in the United States and Canada

Reviewing published coccinellid surveys we found that the number of adventive species has increased steadily over the last century while the average proportion of native individuals has remained fairly constant until 1987 followed by a rapid decrease between 1987 and 2006. Seven long-term studies indicated that the total density of coccinellids increased by an average of 14% following establishment of adventive species, but this increase was not significant and in 4 of 7 cases the total density of coccinellids actually decreased following establishment. Similarly, no significant difference was found in comparisons of diversity across all studies. These results illustrate that even with multiple long-term data sets it is currently difficult to make any general conclusions regarding the impact adventive coccinellids have had on native coccinellid assemblages. However, it is clear that specific systems and species have seen major shifts in recent years. For example, adventives have become the dominant species in a third of the assemblages where they are found. Focusing on two formerly common native species, Adalia bipunctata and Coccinella novemnotata, we show they have become rare in their former ranges and discuss potential explanations for this phenomenon.     

Laboratory study of cannibalism and interspecific predation in ladybirds

Abstract.

• 1 In the absence of aphids, adult females of Adalia bipunctata (L.) showed a greater reluctance to eat eggs than males.
• 2 Eggs and young larvae were more vulnerable to cannibalism than older larvae and starved larvae were more vulnerable than well-fed larvae.
• 3 Both egg and larval cannibalism is inversely related to the abundance of aphids.
• 4 Eggs are a better food, in terms of larval growth and survival, than aphids.
• 5 In the absence of aphids interspecific predation occurred, but not equally, between the coccinellids A.bipunctata, A.decempunctata (L.), Coccinella septempunctata L. and C.undecempunctata L.
• 6 Larvae and adults of A. bipunctata and C.septempunctata were reluctant to eat conspecific eggs painted with a water extract of the other species' eggs and larvae of C. septempunctata were more likely to die after eating a few eggs of A.bipunctata than vice versa.
• 7 These results indicate that cannibalism occurs mainly when aphid prey is scarce and is adaptive in that it improves the chances of survival, and coccinellids, to varying degrees, are defended against interspecific predation.

     

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.     

The co-occurrence of an introduced biological control agent (Coleoptera: <Emphasis Type="Italic">Coccinella septempunctata</Emphasis>) and an endangered butterfly (Lepidoptera: <Emphasis Type="Italic">Lycaeides melissa samuelis</Emphasis>)

Whether a biological control agent presents a non-target risk to a native species depends if they co-occur spatially and temporally, and if the agent will harm the native species. We sampled two study sites during 1993 in Minnesota and Wisconsin to survey predators and parasitoids of the extant populations of the United States federally endangered Karner blue butterfly, Lycaeides melissa samuelis. We found the introduced coccinellid Coccinella septempuntata co-occurring spatially and temporally with eggs, larvae and adults of L. m. samuelis. The two species were also observed together on the latters sole host plant, Lupinus perennis, and in Wisconsin, an adult C. septempunctata was observed consuming second instar larvae of L. m. samuelis. Using a simple model to hypothesize the risk that C. septempunctata presents to L. m. samuelis, we showed that increases in predator density could greatly increase mortality to L. m. samuelis. At these sites, C. septempunctata were reproducing and had access to summer aphids and suitable overwintering habitat. Nearby agricultural crops could provide spring aphids for oogenesis, and assist with C. septempunctata population build-up. Maintaining a minimum isolation distance between agricultural crops known to harbor aphids and extant L. m. samuelis populations may need to be considered as part of the butterfly management program.     

Interactions between the fungal pathogen Beauveria bassiana and three species of coccinellid: Harmonia axyridis, Coccinella septempunctata and Adalia bipunctata

Harmonia axyridis is a predatory coccinellid, native to central and eastern Asia. It has been available in many countries for use as a biological control agent of pest aphids and scale insects. In many of these countries, including the USA, H. axyridis has established. It is now considered an invasive alien species for a number of reasons, including its impact on functional biodiversity. Beauveria bassiana is known to be a natural mortality agent of overwintering coccinellids and is a potential candidate for the biological control of H. axyridis. In this paper we compare the susceptibility of three species of coccinellid, H. axyridis (cultures derived from Japan and UK), Coccinella septempunctata and Adalia bipunctata to infection by B. bassiana (commercial strain GHA) after exposure at three doses (10⁵, 10⁷, 10⁹ conidia ml⁻¹). The two subpopulations of H. axyridis (Japan and UK) were more resistant to B. bassiana infection than either A. bipunctata or C. septempunctata. This is exemplified by the median lethal doses at 10 days post-inoculation (LD₅₀) of 10^6.2, 10^6.0, 10^8.3, 10^9.6 conidia ml⁻¹ for A. bipunctata, C. septempunctata, H. axyridis (Japan) and H. axyridis (UK), respectively. Only doses of 10⁹ conidia ml⁻¹ resulted in mortality of H. axyridis, in contrast, 80% of C. septempunctata and 70% of A. bipunctata exposed to 10⁷ conidia ml⁻¹ of B. bassiana succumbed to infection. The fecundity (cumulative mean egg production over 10 days) of A. bipunctata and H. axyridis (UK) was also assessed. The fecundity of C. septempunctata could not be assessed because this species requires diapause prior to the onset of reproduction and these studies were on beetles that had recently eclosed (2–8 weeks). Harmonia axyridis (Japan) produced no eggs in most treatments including the control and so was excluded from analysis. High dose (10⁹ conidia ml⁻¹) inoculation reduced the fecundity of A. bipunctata to zero but egg production was similar for individuals inoculated with doses of 10⁵, 10⁷ conidia ml⁻¹ and control individuals. In contrast, all doses of B. basssiana reduced H. axyridis (UK) egg production dramatically. We discuss these results in relation to the potential for control of H. axyridis using B. bassiana.     

Predation and avoidance behaviour in aphid‐ladybird interactions of native and invasive ladybirds in Europe

1. While detrimental effects of invasive predators on native species are well documented, we often lack a mechanistic understanding of the invasion success. Lack of prey avoidance behaviour can lead to higher consumption rates by invasive predators compared to native predators. This competitive advantage is expected to contribute to the invasion success of non‐native predators.
2. We compared aphid consumption and cue avoidance behaviour of aphids between four native ladybird species (Coccinella septempunctata, Adalia bipunctata, Propylea quatuordecimpunctata, and Hippodamia variegata) and the invasive Asian ladybird Harmonia axyridis.
3. The invasive H. axyridis and the native C. septempunctata consumed more aphids than the three smaller native ladybird species. In line with our expectations, aphids avoided leaves bearing cues of most native ladybird species but not of the invasive H. axyridis.
4. Our results indicate that body size rather than ladybird origin determined aphid predation rates. The lack of aphid avoidance behaviour towards cues of H. axyridis indicates that they were not able to recognise the chemical cues of the invasive predator.
5. Relatively large body size and the absence of cue avoidance in aphids might benefit the invasive H. axyridis, particularly in comparison to smaller native ladybird species. The absence of avoidance behaviour in aphids might lead to even higher predation rates of H. axyridis under more natural conditions.

     

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.     

Intraguild predation and successful invasion by introduced ladybird beetles

Introductions of two ladybird beetle (Coleoptera: Coccinellidae) species, Coccinella septempunctata and Harmonia axyridis, into North America for aphid biocontrol have been followed by declines in native species. We examined intraguild predation (IGP) between larvae of these two exotic species and larvae of the two most abundant native coccinellids in eastern Washington State, C. transversoguttata and Hippodamia convergens. In pairings between the two native species in laboratory microcosms containing pea (Pisum sativum) plants, neither native had a clear advantage over the other in IGP. When the natives were paired with either Harmonia axyridis or C. septempunctata, the natives were more frequently the victims than perpetrators of IGP. In contrast, in pairings between the exotic species, neither had an IGP advantage, although overall rates of IGP between these two species were very high. Adding alternative prey (aphids) to microcosms did not alter the frequency and patterns of relative IGP among the coccinellid species. In observations of encounters between larvae, the introduced H. axyridis frequently survived multiple encounters with the native C. transversoguttata, whereas the native rarely survived a single encounter with H. axyridis. Our results suggest that larvae of the native species face increased IGP following invasion by C. septempunctata and H. axyridis, which may be contributing to the speed with which these exotic ladybird beetles displace the natives following invasion.     

Ovarian dynamics and oosorption in two species of predatory lady beetles (Coleoptera: Coccinellidae)

Abstract Ovarian development and oviposition dynamics of two species of lady beetle, Coccinella septempunctata L. and C. transversoguttata richardsoni Brown, are examined in laboratory experiments in which pea aphids (Acyrthosiphon pisum Harris) are provided ad libitum and then removed. Both species respond to prey removal by stabilizing at lower body weights, and by laying progressively fewer and smaller eggs of reduced viability, until oviposition ceases altogether after several days of starvation. Dissections of females after prey removal reveal similar patterns of oosorption in both species. However, C. septempunctata reduces oviposition more rapidly after prey removal than does C. transversoguttata. When prey are again provided, C. septempunctata soon lay as many eggs as previously but C. transversoguttata lay fewer. Females, especially of C. septempunctata, that stop producing and resorb eggs in the absence of prey lay more eggs subsequently than do females that feed continually on prey provided ad libitum and lay eggs throughout the experiment. Thus, although both species are responsive to a rapid change in prey availability, C. septempunctata appears to be especially responsive. Rapid responses to changes in prey availability may contribute to the greater abundance and reproductive success of this introduced species relative to the native C. transversoguttata in western North American alfalfa fields that exhibit widely varying pea aphid densities. However, both species engage in oosorption as a means of reserving resources under poor prey conditions and enhancing future reproductive effort when prey conditions improve.     

Intraguild predation by Harmonia axyridis (Coleoptera: Coccinellidae) on native insects in Europe: molecular detection from field samples

Intraguild predation (IGP) is a potential mechanism of negative effects on native species populations by invasive non‐native species such as Harmonia axyridis. Molecular techniques (polymerase chain reaction) were used to probe for the presence of various insect (coccinellid, syrphid and chrysopid) prey DNA in the guts of 177 H. axyridis larvae field‐collected in England, France, Germany, Slovakia and the Czech Republic in 2010. Three of the four target prey species were detected in the guts of H. axyridis at the following rates: Adalia decempunctata 9.6%, Adalia bipunctata 2.8% and Episyrphus balteatus 2.8%. IGP on Chrysoperla carnea was not detected. IGP detection of at least one target species was made in England, France, Slovakia and the Czech Republic, but not in Germany. These results strengthen the evidence that H. axyridis is a very generalist predator. Results are discussed in the context of their ecological significance.