Testing semiochemicals from aphid,plant and conspecific: attraction of Harmonia axyridis

Abstract Harmonia axyridis Pallas (Coleoptera: Coccinellidae) is an invasive specie affecting the dynamics and composition of several guilds. Nowadays, no biological control method is available to reduce the populations of this harmful coccinellid. Attractants and semiochemicals seem to be the best alternative but only few studies have tested the impact of semiochemicals on this Asian lady beetle. In this work, through wind‐tunnel experiments, semiochemicals from aphids (Z,E‐nepetalactone, [E]‐β‐farnesene, α‐pinene and β‐pinene), from coccinellids ([‐]‐β‐caryophyllene) and from the nettle Urtica dioica L. were evaluated as potential attractants. The nettle volatile compounds ([Z]‐3‐hexenol and [E]‐2‐hexenal) were extracted using a Clevenger Apparatus^® and identified by headspace gas chromatography–mass spectroscopy. In the wind‐tunnel experiments, the main components of the aphid alarm pheromone as well as a component of the aphid sexual pheromone strongly attracted both sexes of the Asian lady beetle while (‐)‐β‐caryophyllene only attracted few individuals and had no impact on the males. The nettle extract as well as the (Z)‐3‐hexenol oriented both males and females to the odor source. The (E)‐2‐hexenal was shown to have no effect on females even if this green leaf volatile attracted males. Because Z,E‐nepetalactone was identified as the most efficient attractant in the wind‐tunnel experiments, this volatile was also tested in a potato field where H. axyridis has been showed to respond to this semiochemical. This study highlighted that Z,E‐nepetalactone orientated the Asian lady beetle H. axyridis under natural conditions, indicating that this volatile compound could certainly help for an efficient biological control approach against this invasive specie.     

Cover Caption

Like most aphid species, the Vetch aphid, Megoura viciae, produces honeydew while feeding on broad bean, Vicia faba. After being rejected on the host plant surface, honeydew releases a kairomonal blend of volatile molecules that guide aphid predators, including the Asian lady beetle, Harmonia axyridis, toward aphid colonies (Credits F.J. Verheggen, see pages 498–506).     

A window of opportunity: Subdominant predators can use suboptimal prey

Introduced species have been linked to declines of native species through mechanisms including intraguild predation and exploitative competition. However, coexistence among species may be promoted by niche partitioning if native species can use resources that the invasive species cannot. Previous research has shown that some strains of the aphid Aphis craccivora are toxic to a competitively dominant invasive lady beetle, Harmonia axyridis. Our objective was to investigate whether these aphids might be an exploitable resource for other, subdominant, lady beetle species. We compared larval development rate, survival, and adult weight of five lady beetle species in no‐choice experiments with two different strains of A. craccivora, one of which is toxic to H. axyridis and one that is nontoxic. Two lady beetle species, Cycloneda munda and Coleomegilla maculata, were able to complete larval development when feeding on the aphid strain that is toxic to H. axyridis, experiencing only slight developmental delays relative to beetles feeding on the other aphid strain. One species, Coccinella septempunctata, also was able to complete larval development, but experienced a slight reduction in adult weight. The other two lady beetle species, Hippodamia convergens and Anatis labiculata, demonstrated generally low survivorship when consuming A. craccivora, regardless of aphid strain. All five species showed increased survival and/or development relative to H. axyridis on the “toxic” aphid strain. Our results suggest that this toxic trait may act as a narrow‐spectrum defense for the aphids, providing protection against only some lady beetle enemies. For other less‐susceptible lady beetles, these aphids have the potential to provide competitive release from the otherwise dominant H. axyridis.     

Attraction of the predator,Harmonia axyridis (Coleoptera: Coccinellidae), to its prey,Myzus persicae (Hemiptera: Aphididae), feeding on Chinese cabbage

The predatory multicolored Asian lady beetle, Harmonia axyridis, was attracted to volatiles released from Chinese cabbage infested by the green peach aphid, Myzus persicae, in T-tube olfactometer choice tests. However, lady beetle adults and larvae did not respond to clean air, Chinese cabbage alone or green peach aphid alone. Of different prey densities, H. axyridis adults were most attracted to Chinese cabbage infested by 60 M. persicae adults after 24 h. However, H. axyridis larvae were not attracted to Chinese cabbage infested by M. persicae. Mechanically damaged Chinese cabbage attracted neither lady beetle adults nor larvae. Predatory adults were attracted to 60 M. persicae adults after 24 and 48 h, and to 90 M. persicae adults after 12 h, suggesting that the predatory response depends on the prey density. Lady adult beetles did not prefer the volatiles induced by Diamondback moth, Plutella xylostella, indicating that specific host insect specificity attracts respective natural enemies. It can be explained that the volatile compounds emitted from the host plant as a result of herbivore attack preferred by the specific insect species.     

Occurrence of cotton aphids (Aphis gossypii) and lady beetles (Hamonia axyridis) on Hibiscus syriacus Linne: Are the aphids a pest of cucurbits?

Populations of cotton aphid on Hibiscus syriacus increased rapidly from 17 to 24 May 2007, and then decreased as its predator, the lady beetle Hamonia axyridis, increased in number. There was a 10 day time lag between peak populations of aphids and lady beetles. The infestation of aphids on H. syriacus produced some damage, but H. syriacus recovered soon after the lady beetles arrived. Cotton aphid clones from H. syriacus were transferred to other summer host plants: to five different vegetables on two dates, and to cucumber on three dates. Apart from one case where reproduction occurred on eggplant, most H. syriacus aphid clones did not survive on the vegetables. The cotton aphid on H. syriancus was prey and a food source for H. axyridis and acted to conserve natural enemies.     

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.     

Comparison of native and non‐native predator consumption rates and prey avoidance behavior in North America and Europe

Novel predator–prey interactions can contribute to the invasion success of non‐native predators. For example, native prey can fail to recognize and avoid non‐native predators due to a lack of co‐evolutionary history and cue dissimilarity with native predators. This might result in a competitive advantage for non‐native predators. Numerous lady beetle species were globally redistributed as biological control agents against aphids, resulting in novel predator–prey interactions. Here, we investigated the strength of avoidance behavior of the pea aphid (Acyrthosiphon pisum) toward chemical cues of native lady beetles and non‐native Asian Harmonia axyridis and European Coccinella septempunctata and Hippodamia variegata in North America, hypothesizing that cues of non‐native lady beetles induce weaker avoidance behavior than cues of co‐evolved native lady beetles. Additionally, we compared aphid consumption of lady beetles, examining potential predation advantages of non‐native lady beetles. Finally, we compared cue avoidance behavior between North American and European pea aphid populations and aphid consumption of native and non‐native lady beetles in North America and Europe. In North America, pea aphids avoided chemical cues of all ladybeetle species tested, regardless of their origin. In contrast to pea aphids in North America, European pea aphids did not avoid cues of the non‐native H. axyridis. The non‐native H. axyridis and C. septempunctata were among the largest and most voracious lady beetle species tested, on both continents. Consequently, in North America non‐native lady beetle species might have a competitive advantage on shared food resources due to their relatively large body size, compared to several native American lady beetle species. In Europe, however, non‐native H. axyridis might benefit from missing aphid cue avoidance as well as a large body size. The co‐evolutionary time gap between the European and North American invasion of H. axyridis likely explains the intercontinental differences in cue avoidance behavior and might indicate evolution in aphids toward non‐native predators.     

Control of Aphis gossypii and Myzus persicae (Hemiptera: Aphididae) by a flightless strain of Harmonia axyridis (Coleoptera: Coccinellidae) on green pepper plants in open fields

The cotton aphid Aphis gossypii Glover and the green peach aphid Myzus persicae (Sulzer) are economically important pests with a worldwide distribution. We evaluated the efficacy of releasing a flightless adult strain of the multicolored Asian lady beetle Harmonia axyridis (Pallas) as a control measure against these aphids on green pepper plants in open fields. Flightless H. axyridis adults were observed on the green pepper plants in the releasing plots throughout the experimental period and were found to be effective biocontrol agents, markedly decreasing the numbers of aphids. These results suggest that adults of this flightless strain of H. axyridis are effective in controlling aphids on green pepper plants in open fields.     

Symbiont‐mediated chemical defense in the invasive ladybird Harmonia axyridis

The volatile alkylpyrazines methyl‐ and methoxypyrazines (MPs) present in the reflex bleeds of coccinellid beetles such as the harlequin ladybird beetle Harmonia axyridis are important semiochemicals that function in antipredatory defense behavior. Pyrazines have also been coadapted from a primarily defensive role into pheromones that function in intraspecific communication, attraction, and aggregation behavior. However, the biosynthesis of MPs in ladybird beetles is poorly understood. Here, we tested the hypothesis that MPs could be produced by microbial symbionts in H. axyridis, which generates four different MPs. The evaluation of tissue‐specific MP production showed that MP concentrations were highest in the gut tissue and hemolymph of the beetles rather than the fat body tissue as the presumed site of MP biosynthesis. Furthermore, manipulation of gut microbiota by antibiotic‐containing diets resulted in a lower MP content in adult beetles. The analysis of the bacterial community of the digestive tract revealed the presence of bacteria of the genera Serratia and Lactococcus which are reportedly able to produce MPs. In line with the known diet‐dependent production of MP in H. axyridis, we determined that the presence or relative abundance of some of the potential MP producers (Enterococcus and Staphylococcus) is also diet‐dependent. We hypothesize a potential role of the microbiota in MP production in H. axyridis as a possible example for outsourcing the synthesis of ecologically important semiochemicals to its gut bacteria.     

Control of Myzus persicae and Lipaphis erysimi (Hemiptera: Aphididae) by adults and larvae of a flightless strain of Harmonia axyridis (Coleoptera: Coccinellidae) on non-heading Brassica cultivars in the greenhouse

The green peach aphid [Myzus persicae (Sulzer)] and turnip aphid [Lipaphis erysimi (Kaltenbach)] are economically important pests with a worldwide distribution. We have evaluated the efficacy of releasing adults and larvae of a flightless strain of the multicolored Asian lady beetle (Harmonia axyridis Pallas) as a control measure against these aphids on plants of non-heading Brassica cultivars. Both adults and larvae of H. axyridis were observed to be effective biocontrol agents, markedly decreasing the numbers of aphids. The residence duration of adults was longer than that of larvae. The proportion of non-marketable plants damaged by aphids was lower in plots into which either adults or adults and larvae of H. axyridis had been released. These results suggest that both adults and larvae of this flightless strain of H. axyridis are effective in controlling aphids on plants of non-heading Brassica cultivars.     

Sibling and non-sibling cannibalism by larvae of a lady beetleHarmonia axyridis Pallas (Coleoptera: Coccinellidae) in the field

Sibling (cannibalism among siblings) and non-sibling cannibalism (cannibalism among non-siblings) were studied in a natural population of a lady beetle, Harmonia axyridisPallas . Of all the eggs laid (n=2269), 24.76% (n=562) were killed by sibling cannibalism and 36.10% (n=819) were killed by non-sibling cannibalism. Sibling cannibalism occurred constantly and intensively in most egg batches throughout the entire oviposition period. On the other hand, non-sibling cannibalism was more intense in the middle and late oviposition periods, and when the egg batches were close to an aphid colony. This may be due to the high density of H. axyridis larvae relative to aphid density in the middle and late oviposition periods and also the larvae searching intensively near an aphid colony.     

Bacteria may contribute to distant species recognition in ant–aphid mutualistic relationships

Mutualistic interactions between ant and aphid species have been the subject of considerable historical and contemporary investigations, the primary benefits being cleaning and protection for the aphids and carbohydrate‐rich honeydew for the ants. Questions remained, however, as to the volatile semiochemical factor influencing this relationship. A recent study highlighted the role of bacterial honeydew volatile compounds in ant attraction. Here, ant's ability to distantly discriminate 2 aphid species was investigated based on bacterial honeydew semiochemicals emissions using a two‐way olfactometer. Both the mutualistic aphid Aphis fabae L. and the nonmyrmecophilous aphid Acyrthosiphon pisum Harris were found to be attractive for the ant Lasius niger L. The level of attraction was similar in both assays (control vs. one of the aphid species). However, when given a choice between these 2 aphid species, ants showed a significant preference for Aphis fabae. Honeydew volatiles, mostly from bacterial origins, are known to be a key element in ant attraction. Using the same olfactometry protocol, the relative attractiveness of volatiles emitted by honeydews collected from each aphid species and by bacteria isolated from each honeydew was investigated. Again, ants significantly preferred volatiles released by Aphis fabae honeydew and bacteria. This information suggests that microbial honeydew volatiles enable ants to distantly discriminate aphid species. These results strengthen the interest of studying the occurrence and potential impact of microorganisms in insect symbioses.     

Development of lady beetle attractants from floral volatiles and other semiochemicals for the biological control of aphids

Aphids are among the most destructive phytophagous pests of host plants, because of their rapid reproduction, parthenogenesis, extensive crop damage, and the transmission of many plant viruses. Since lady beetles are important predatory natural enemies of aphids, developing lady beetle attractants to increase their field abundance is vital for aphid control. Floral volatiles and other semiochemicals are reportedly attractive to lady beetles. In this research, a total of 58 floral volatiles were tested by Y-tube olfactometer assays, among which 29 were highly attractive to both Harmonia axyridis (Coleoptera: Coccinellidae) and Coccinella septempunctata (Coleoptera: Coccinellidae). Meanwhile, the results of wind tunnel trials showed that only isoamyl acetate, α-humulene, trans-3-hexen-1-ol, methyl salicylate, and β-pinene lure these two species. Thereafter, 15 semiochemicals from pests, natural enemies, and pest-infested crops were mixed with the selected floral volatiles, to determine optimum formulations for attracting lady beetles through wind tunnels and further field trials. Eventually, formulas (1) α-humulene: β-pinene: methyl salicylate: trans-3-hexen-1-ol = 1:3:3:10; (5) α-humulene: β-pinene: methyl salicylate:1-nonanal = 1:3:3:10; (8) α-humulene: β-pinene: methyl salicylate: indole = 1:3:3:10 (1, 5, and 8 are labels used for the various formulations in field trials) were successfully verified to be attractive to lady beetles in both pumpkin and wheat fields. These formulations will be of great significance in developing integrated pest management strategies for aphid control.     

Horizontal transmission of a microsporidium from the convergent lady beetle, Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae), to three coccinellid species of Nova Scotia

Convergent lady beetles, Hippodamia convergens Guérin-Méneville, are a popular choice for aphid control in North America. An unidentified microsporidium was found in H. convergens adults that were purchased from a commercial insectary in 2004. This study examined egg cannibalism and egg predation as a means of horizontal transmission of the unidentified microsporidium among H. convergens larvae and three coccinellid species found in Nova Scotia: Coccinella septempunctata (seven-spotted lady beetle), C. trifasciata perplexa (three-banded lady beetle), and Harmonia axyridis (multicolored Asian lady beetle). The microsporidium was transmitted with 100% efficiency when first instars fed on microsporidia-infected eggs. Mean spore count data from smear preparations of infected beetles suggest that the infection was as heavy in C. trifasciata perplexa (a native coccinellid) (11.2 ± 0.96 spores/100 μm²) as it was in H. convergens (the natural host) (12.8 ± 1.16) but lighter in the introduced species C. septempunctata (7.5 ± 0.65) and H. axyridis (0.8 ± 0.11). For all of the beetle species examined, larval development was significantly longer for microsporidia-infected individuals than for their uninfected cohorts. The microsporidium had no effect on larval mortality. Based on the results of this study, field-collected H. convergens should be examined for microsporidia and uninfected individuals should be used to rear individuals for release in biological control programs. However, this is unlikely to happen because H. convergens are relatively easy and inexpensive to collect from their overwintering sites for redistribution.     

First Evidence of a Volatile Sex Pheromone in Lady Beetles

To date, volatile sex pheromones have not been identified in the Coccinellidae family; yet, various studies have suggested that such semiochemicals exist. Here, we collected volatile chemicals released by virgin females of the multicolored Asian lady beetle, Harmonia axyridis (Pallas), which were either allowed or not allowed to feed on aphids. Virgin females in the presence of aphids, exhibited “calling behavior”, which is commonly associated with the emission of a sex pheromone in several Coleoptera species. These calling females were found to release a blend of volatile compounds that is involved in the remote attraction (i.e., from a distance) of males. Gas Chromatography-Mass Spectrometry (GC-MS) analyses revealed that (–)-β-caryophyllene was the major constituent of the volatile blend (ranging from 80 to 86%), with four other chemical components also being present; β-elemene, methyl-eugenol, α-humulene, and α-bulnesene. In a second set of experiments, the emission of the five constituents identified from the blend was quantified daily over a 9-day period after exposure to aphids. We found that the quantity of all five chemicals significantly increased across the experimental period. Finally, we evaluated the activity of a synthetic blend of these chemicals by performing bioassays which demonstrated the same attractive effect in males only. The results confirm that female H. axyridis produce a volatile sex pheromone. These findings have potential in the development of more specific and efficient biological pest-control management methods aimed at manipulating the behavior of this invasive lady beetle.     

Influence of the prey aphid Uroleucon nigrotuberculatum parasitizing Solidago canadensis on the larval and adult survivorship of the predatory ladybird beetle Harmonia axyridis

The ladybird beetle Harmonia axyridis is an aphidophagous natural enemy in Japan. The alien plant Solidago canadensis is widespread in Japanese agricultural landscapes, and the alien aphid Uroleucon nigrotuberculatum parasitizes the plant. We examined the quality of the aphid as food for all developmental stages of H. axyridis. First-instar larvae fed the aphid died within 2 days. Larvae at later developmental stages survived for significantly longer periods but died before pupation. Adults fed the aphid also died within 10 days. These results suggest that U. nigrotuberculatum parasitizing S. canadensis is unsuitable for H. axyridis during the beetle’s entire life cycle.     

Honeydew amino acids in relation to sugars and their role in the establishment of ant-attendance hierarchy in eight species of aphids feeding on tansy (Tanacetum vulgare)

Abstract. The ratio of the concentration of honeydew total amino acids to total sugars in the honeydew of eight species of aphids, all feeding on tansy, Tanacetum vulgare (L.), was determined and correlated with honeydew production and ant‐attendance. The honeydew of the five ant‐attended aphid species [Metopeurum fuscoviride (Stroyan), Trama troglodytes (v. Hayd), Aphis vandergooti (Börner), Brachycardus cardui (L.), Aphis fabae (Scopoli)] was rich in total amino acids, ranging from 12.9 to 20.8 nmol µL^?1 compared with the unattended aphid Macrosiphoniella tanacetaria (Kalt.) with only 3 nmol µL^?1. Asparagine, glutamine, glutamic acid and serine (all nonessential amino acids) were the predominant amino acids in the honeydew of all species. The total concentration of amino acids in the phloem sap of tansy was much higher (78.7 nmol µL^?1) then in the honeydew samples, and the predominant amino acids were glutamate (34.3%) and threonine (17.7%). A somewhat unexpected result was the finding that those aphid species with the highest total amino acid concentration in the honeydew always had the highest concentration of sugars. The lowest amino acid–sugar combined value was 104–28.8 nmol µL^?1 in the non ant‐attended species M. tanacetaria, and the highest value was an average of 270–89.9 nmol µL^?1 for the three most intensely attended aphid species M. fuscoviride, A. vandergooti and T. troglodytes. There is no evidence that any single amino acid or group of amino acids in the honeydew acted as an attractant for ant‐attendance in these eight aphid species. The richness of the honeydew (rate of secretion × total concentration of sugars), along with the presence of the attractant sugar melezitose, comprised the critical factors determining the extent of ant‐attendance of the aphids feeding on T. vulgare. The high total amino acid concentration in sugar‐rich honeydews can be explained by the high flow‐through of nutrients in aphids that are particularly well attended by ants.     

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.     

Orientation behavior of Propylaea japonica toward visual and olfactory cues from its prey–host plant combination

The lady beetle Propylaea japonica (Thunberg) (Coleoptera: Coccinellidae) is an important predator of aphids in agroecosystems. The inundative release of coccinellid beetles can be an effective biological control strategy. An understanding of how biological control agents perceive and use stimuli from host plants is the key to successfully implement commercially produced predators. Here, we studied the relative role of visual and volatile cues. Dual‐choice assays using foraging‐naïve and foraging‐experienced P. japonica adults were conducted using cotton plants [Gossypium hirsutum L. (Malvaceae)] with or without infestation by the cotton aphid, Aphis gossypii (Glover) (Hemiptera: Aphididae). Overall, experienced beetles were more attracted than naïve beetles toward cues associated with aphid‐infested plants. Experienced beetles were also more responsive to olfactory cues compared with naïve beetles. Both foraging‐naïve and ‐experienced lady beetles integrate olfactory and visual cues from plants infested with aphids, with an apparently greater reliance on olfactory cues. The results suggest that foraging experience may increase prey location in P. japonica.     

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

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