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.     

Evidence for utilization of Diptera in the diet of field-collected coccinellid larvae from an antibody-based detection system

Aphidophagous coccinellid larvae have a wide range of potential prey in alfalfa and during times of low aphid abundance, larvae may supplement their diet with alternative prey. To understand the effects of the seasonal aphid availability on alternative prey use, an order-specific monoclonal antibody, DrosW-VI-B8, was used to examine the frequency of dipteran predation by these important natural enemies. Over 400 larvae were hand-collected from alfalfa and, in parallel, arthropod abundance was recorded. Harmonia axyridis and Coccinella septempunctata larvae were abundant early in the season when aphid populations were at their peak and Coleomegilla maculata larvae were collected later in the season when potato leafhoppers were abundant in the alfalfa. A relatively low proportion of field-collected H. axyridis, C. septempunctata, and C. maculata tested positive for dipteran proteins throughout the season. Similar to prior studies examining stage differences in coccinellid food breadth, older instars tested positive for dipteran proteins (3rd instar, 6% positive; 4th instar, 7% positive) but no early instars screened positive. This study provides a valuable insight into the trophic linkages that exist between coccinellid larvae and Diptera.     

Do microsporidia function as “biological weapon” for Harmonia axyridis under natural conditions?

Invasive alien species, such as the multicoloured Asian ladybird Harmonia axyridis, are often regarded as major drivers of biodiversity loss. Therefore understanding which characteristics or mechanisms contribute to their invasive success is important. Here the role of symbiotic microsporidia in the hemolymph of H. axyridis was investigated in the context of intraguild predation between wild‐caught H. axyridis and the native ladybird species Coccinella septempunctata. The microsporidia were recently discussed to contribute to the unpalatability of Harmonia for other coccinellids during intraguild predation and to function as “biological weapons”. In the present study, visual detection of microsporidia in hemolymph samples revealed that 73.5 % of H. axyridis were infected. Intraguild predation experiments between larvae of the two species showed a significant competitive advantage for H. axyridis, even against larger larvae of C. septempunctata. Adult C. septempunctata always killed and fed on H. axyridis larvae. However only 11.4 % (4 of 47) of C. septempunctata that fed on infected H. axyridis died within 4 months. In contrast to previous studies this suggests that microsporidia or harmonine, the chemical defense compound of H. axyridis, do not lead to death of C. septempunctata preying on larvae of H. axyridis. Instead our results support the idea that competitive advantage during intraguild predation greatly facilitates the success of H. axyridis and that this may help this highly invasive species to outcompete native species. The impact of microsporidia on Harmonia itself as well as on interspecific interactions require further studies.     

Effect of stinging nettle habitats on aphidophagous predators and parasitoids in wheat and green pea fields with special attention to the invader Harmonia axyridis Pallas (Coleoptera: Coccinellidae)

The relative occurrence and seasonal abundance of aphids and their natural enemies were visually assessed between May and July 2005–2006 in four types of habitats located in Gembloux (Namur province, Belgium): green pea, wheat and stinging nettle either planted in or naturally growing in woodland adjacent to these crops. Results showed that: (i) Acyrthosiphon pisum Harris, Sitobion avenae F. and Microlophium carnosum Buckton were the most common aphid species, respectively, on green pea, wheat and stinging nettle either in or near field crops; (ii) stinging nettle and field crops shared several important aphidophagous insect species such as the ladybird Coccinella septempunctata L., hoverfly Episyrphus balteatus De Geer and braconid wasp Aphidius ervi Haliday; (iii) the shared beneficial species were typically recorded earlier on stinging nettles than on crops; and (iv) the spatial occurrence of the invasive ladybird Harmonia axyridis Pallas was distinctly associated with stinging nettles, particularly in 2005. Stinging nettles and field crops partially coincide in time, enabling the movement of natural enemies among them. These findings suggest that the presence of stinging nettles in landscapes seems to enhance the local density of aphidophagous insect communities necessary for aphid biocontrol in field crops.     

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.     

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.     

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.     

Changes in δ 13C stable isotopes in multiple tissues of insect predators fed isotopically distinct prey

Traditionally, researchers have used measurements of carbon stable isotopes to infer the composition of consumers’ diets. However, since consumer’s tissues may process carbon isotopes differently, particularly following a diet shift, it is possible to use measurements of carbon isotopes in multiple tissues to determine not only the composition of an individual’s diet, but also the temporal dynamics thereof. This study examined how stable isotopes of carbon (¹³C/¹²C, expressed as δ ¹³C) changed in different adult tissues of two predacious beetles, Harmonia axyridis and Coccinella septempunctata (Coleoptera: Coccinellidae). In the laboratory, we switched ladybeetles from a C3-based diet (soybean aphids, Aphis glycines) to a C4-based one (corn leaf aphids, Rhopalosiphum maidis). The δ ¹³C of metabolically active tissues such as the body fat and reproductive organs changed rapidly (≤5 days) following the diet shift. Tissues expected to be more metabolically inert, such as wings, changed more slowly over the same period. Although these general patterns were largely similar between males and females, females had more rapid changes in δ ¹³C in fat and reproductive tissues. However, females showed a significant depletion in δ ¹³C after 10 days, while males’ δ ¹³C continued to increase. Given the results of this experiment, it is now possible to distinguish between ladybeetles eating a mixed diet (beetles with multiple tissues at similar, intermediate, equilibrial δ ¹³C signatures) from those that have shifted diets (beetles with different tissues at distinctly different δ ¹³C values). Thus, this approach can be used broadly to infer not only what constitutes the diet of a consumer, but also the temporal history of dietary intake.     

Ladybird population dynamics in potato: comparison of native species with an invasive species, Harmonia axyridis

Following the detection of the harlequin ladybird, Harmonia axyridis, in 2003 in potato crops in Belgium, a study was carried out between 2004 and 2006 on the phenology of this species compared to native species in potato. The results confirmed the success of H. axyridis, with high population levels in 2004 and 2005. In 2006, aphid populations were very low and no H. axyridis larvae were sampled in potato, but the indigenous species Coccinella septempunctata and Propylea quatuordecimpunctata were detected. A species by species comparison of the date of first larvae detection, the larvae population peak, and the difference between this peak and the aphid population peak was performed. Results showed a clear correlation between C. septempunctata and P. quatuordecimpunctata and potato aphids, with a delay of 3.5 and 6.5 days between the aphid and ladybird population peaks for the two native species. H. axyridis arrived 7–8 days after the two indigenous species and the larval peak population occurred 15.8 days after the aphid population peak. This meant that H. axyridis had to complete its larval development with very low aphid populations or even with no aphids at all. The reason for its late arrival and the possible food resources used by H. axyridis larvae are discussed.     

三种瓢虫集团内捕食卵对初龄幼虫生长发育的影响

种内和种间捕食卵现象常见于对食蚜瓢虫的研究报道中。源自亚洲、入侵北美和欧洲的异色瓢虫(Harmonia axyridis)由于卵含有生物碱而被认为可能是威胁本土瓢虫生存的原因,但该推测只有在明确异色瓢虫在原产地是否对本土瓢虫具有类似负面影响后,才能确证。通过饲喂实验,旨在明确异色瓢虫在原产地是否对本土七星瓢虫(Coccinella septempunctata)和龟纹瓢虫(Propylea japonica)具有食卵负面作用,为揭示异色瓢虫入侵机理提供依据。实验中用蚜虫(对照)和3种瓢虫卵对瓢虫初孵1龄幼虫进行饲喂处理,观察幼虫生长发育指标。对瓢虫初龄幼虫存活表现的分析结果表明:(1)龟纹瓢虫初孵幼虫取食同种卵和七星瓢虫卵后存活至2龄的比率均高于取食异色瓢虫卵的近7倍;(2)七星瓢虫幼虫取食异色瓢虫卵未存活到2龄,但取食其他瓢虫卵和蚜虫后85%以上个体存活至2龄;(3)异色瓢虫初孵幼虫取食同种和其他2种瓢虫卵后有90%以上存活至2龄。龟纹瓢虫和七星瓢虫1龄幼虫取食异种卵比同种卵后的发育历期显著延长,但异色瓢虫并未表现出差异。龟纹瓢虫和异色瓢虫1龄幼虫取食同种和异种卵后的体增重相同,但七星瓢虫取食龟纹瓢虫卵后体增重比取食同种卵减小。研究结果说明,异色瓢虫卵对七星瓢虫和龟纹瓢虫初孵幼虫的生存具有负面影响,反之不然。所以,取食异色瓢虫卵本身并非是导致北美和欧洲本土瓢虫数量减少的原因。     

Change in carbon stable isotope ratios of the predatory bug Orius majusculus after dietary shifts

Orius majusculus Reuter (Hemiptera: Anthocoridae) is an important component of the pest predatory complex in arable crops in Mediterranean areas. It moves between crops searching for prey, and improving knowledge on its dispersal abilities will help to develop conservation biological control strategies. Stable isotope ratios may be used as a tool for tracking insect movements, as the isotopic composition of insect tissues changes to reflect that of their diet when they undergo dietary shifts on moving between isotopically distinct crops. We carried out laboratory diet switch experiments with a stable isotope approach to infer information on dispersal of O. majusculus individuals among C3 and C4 crops to better understand isotopic field data collections. Switching the aphid food source caused a quick change in δ¹³C signatures, regardless of the original and final food source. Changes in the δ¹³C ratio of O. majusculus after diet switching fitted with an exponential model that showed similar turnover rates, and thus half‐lives, between shifting diets up to 20 days. Subsequently, whereas individuals feeding on C4 aphids did not survive, turnover rate decreased in individuals that switched from C4 to C3 aphids. However, δ¹³C traces from the original source remained in the predator until 25 days after switching, and this is enough time to help determine the movement of O. majusculus between crops in the field and to plan the timing of predator sampling and crop practices that may enhance predator ecological services. Orius majusculus that switched to a maize aphid diet showed different turnover rates between sexes, although this did not influence the pattern of switchover.     

Interactions between the parasitoid wasp Dinocampus coccinellae and two species of coccinellid from Japan and Britain

The establishment, spread and increase of the invasive coccinellid Harmonia axyridis Pallas in North America and Britain have coincided with declines in native ladybirds. In Britain, this pattern was predicted soon after H. axyridis was first recorded. However, predictions of the impact that H. axyridis may have on the parasites, parasitoids and pathogens of native coccinellids have been less certain, largely because of uncertainty over whether H. axyridis would become an alternate host for such agents. Dinocampus coccinellae (Schrank) is a braconid parasitoid of ladybirds of the sub-family Coccinellinae. In Japan, this wasp uses both Coccinella septempunctata brucki Mulsant and H. axyridis as hosts, but successfully parasitizes a higher proportion of the former species. Data are here presented that indicate the same is true in Britain, but to a greater extent. This study investigates the interactions of D. coccinellae with C. septempunctata L. and H. axyridis from Japan and Britain. We show that coccinellid activity affects encounter rates with the wasp, with H. axyridis being more active than C. septempunctata in the tests. Escalation rates from investigation to ovipositional attack were higher for C. septempunctata than H. axyridis for both Japanese and British wasps. Wasp emergence was higher, relative to ovipositional attack, from C. septempunctata than from H. axyridis. Wasps did not discriminate between Japanese and British ladybirds of the same species. British wasp eclosion rates were higher from Japanese than from British H. axyridis. We consider both the effect D. coccinellae may have on H. axyridis population demography, and the effect H. axyridis may have on D. coccinellae in Europe.     

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.     

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.     

Heterodynamic processes in Coccinella septempunctata L. (Coccinellidae: Coleoptera): a mini review

Among ladybirds, diapause has evidently been most studied in Coccinella septempunctata L. adults. Coccinella septempunctata (C‐7), the seven spot, has attracted attention both in Europe and the USA for being heterogeneous as to the induction of diapause. A polyphenic character of diapause is a prominent feature in C. septempunctata and this phenomenon generally and often generates voltinism heterogeneity within populations. A greater part of the C‐7 population shows an obligatory univoltine cycle, whereas a smaller proportion is facultatively polyvoltine. Coccinella s. bruckii in Japan is bivoltine, in which the first generation of adults aestivate while the second generation hibernates. This paper reviews this heterodynamic cycle and its importance in the life history of C‐7, as reported from different regions of the world. Heterogeneous voltinism and diapause smooth the progress of a portion of C‐7 populations to take benefit of aphids well into late summer and autumn. Understanding such variation and plasticity in the life history of this species can help in organizing proper biological control attempts using it as a biocontrol agent.     

Stable carbon and nitrogen isotope signatures to determine predator dispersal between alfalfa and maize

The dispersal of Orius majusculus and Coccinella septempunctata between maize and alfalfa during the vegetative and reproductive maize growth periods was investigated, using carbon and nitrogen stable isotope analysis and aphids as herbivore prey at two locations of the NE Iberian Peninsula. The dispersal pattern of O. majusculus and C. septempunctata differs between these crops and also between different moments of the maize growth period. In the vegetative period the pattern was similar for the two predators and alfalfa acted as a source of predators towards maize. During the reproductive period, the dispersal of O. majusculus between the two crops was continuous but biased from maize to alfalfa, which mainly becomes a sink crop. All of the C. septempunctata collected on alfalfa were local and those collected on maize came from alfalfa, but there was no dispersal from maize to alfalfa. The present study increases knowledge of the dispersion of predators between arable crops and can improve habitat and landscape management at the farm scale by enhancing their biological control functions.     

Barcode haplotype variation in north American agroecosystem lady beetles (Coleoptera: Coccinellidae)

DNA barcodes have proven invaluable in identifying and distinguishing insect pests, most notably for determining the provenance of exotic invasives, but relatively few insect natural enemies have been barcoded. We used Folmer et al.’s (1994) universal invertebrate primers and Hebert et al.’s (2004) for Lepidoptera, to amplify 658 bp at the 5′ end of the mitochondrial cytochrome oxidase c subunit I (COI) gene in five species of lady beetles from crop fields in six states in the US Mid‐Atlantic, Plains and Midwest: three native species, Hippodamia convergens Guérin‐Méneville, H. parenthesis (Say) and Coleomegilla maculata (De Geer); and two exotic species, Harmonia axyridis (Pallas) and Coccinella septempunctata Linnaeus. Sequence divergences within species were low, never exceeding 0.9% (Kimura 2‐parameter distances). Sequence divergences between the two Hippodamia species ranged from 14.7 to 16.4%, mirroring the relationships found for other arthropod taxa. Among the exotic species, C. septempunctata sequences were as variable as those of the three native species, while H. axyridis populations comprised a single haplotype. Limited data on two Coleomegilla subspecies, C. m. lengi Timberlake and C. m. fuscilabris (Mulsant), are consistent with their belonging to the same species, although morphological and reproductive data indicate that they represent separate species. Our results support the general utility of COI barcodes for distinguishing and diagnosing coccinellid species, but point to possible limitations in the use of barcodes to resolve species assignments in recently divergent sibling species.     

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

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

Effects of an invading coccinellid on native coccinellids in an agricultural landscape

Seven native coccinellid species inhabited alfalfa, corn, and small grain fields in eastern South Dakota prior to invasion and establishment of Coccinella septempunctata L. Six species occurred in all crops, however, Adalia bipunctata (L.) occurred only in corn. The structure of native coccinellid communities differed significantly for years prior to compared with years after establishment of C. septempunctata in fields of the three agricultural crops. Differences in community structure were accounted for mainly by reduced abundance of two species, C. transversoguttata richardsoni Brown and Adalia bipunctata (L.). Annual abundance of C. transversoguttata richardsoni averaged 20–32 times lower during post-invasion years than in years prior to invasion, depending on crop; while annual abundance of A. bipunctata averaged 20 times lower in corn after invasion. Addition of C. septempunctata to the community did not result in a significant increase in total abundance of coccinellids in the crops. Coccinellid abundance in agricultural crops may be limited by the total abundance of prey or by the availability of other requisites in the landscape as a whole. Therefore, introduction of a new species, while resulting in reductions in native species populations, may not increase total coccinellid abundance, and may therefore have no net effect on biological control of aphid pests.     

Differential sensitivity of an invasive and an indigenous ladybeetle to two reduced‐risk insecticides

The invasive multicoloured Asian lady beetle, Harmonia axyridis (Pallas), and the indigenous twelve spotted lady beetle, Coleomegilla maculata DeGeer (Col., Coccinellidae), are two important generalist predators commonly found in apple orchards in Quebec, Canada. Both species are exposed to two reduced‐risk insecticides, recently adopted to control codling moth, Cydia pomonella (L.) (Lep., Tortricidae) in south‐eastern Canada. Chlorantraniliprole (Altacor^® 35 WG), an anthranilic diamide insecticide, causes paralyses of the muscle cells by interfering with the insect ryanodine receptors, whereas novaluron (Rimon^® EC 10), a benzoylphenyl urea, inhibits the chitin synthesis. The aim of this study was to compare the sensitivity of both the invasive ladybeetle H. axyridis and the indigenous C. maculata to reduced‐risk insecticides through the assessment of lethal effect on eggs and larvae following topical contact, ingestion of treated prey and exposure to fresh residues, at field rates (50.75 g a.i./ha chlorantraniliprole and 100 g a.i./ha novaluron) in laboratory conditions. Eggs of both species were not affected. Following 6 days of residual contact, chlorantraniliprole and novaluron caused more than 98% mortality to larvae of both ladybeetle species. In topical contact and ingestion trials, chlorantraniliprole caused less than 18% mortality to larvae of the two species after 6 days following exposure. Novaluron had a drastically different impact on the two predators. It did not affect the indigenous C. maculata, whereas it killed 91% and 96% of H. axyridis individuals after 6 days, respectively, following topical contact and ingestion. These results illustrate a differential sensitivity to novaluron between two relatively close species (subfamily Coccinellinae), a potential impact on the invasion process by H. axyridis, and consequently on the ladybeetle assemblage in the field.