The role of exotic ladybeetles in the decline of native ladybeetle populations: evidence from long-term monitoring

Expanded Geographical Distribution of Coleomegilla maculata lengi (Coleoptera: Coccinellidae) in North America

Several species of lady beetle native to North America have declined in abundance in the last few decades, often accompanied by contractions in their geographic ranges. Coleomegilla maculata lengi is a lady beetle native to North America that is an important predator of pests in various agroecosystems. Its reported range spans the eastern half of the USA, with no sustained decline in abundance or contraction of its range reported. Indeed, we recently collected several individuals of this lady beetle in central USA roughly 500 km beyond the western edge of its reputed range. We hypothesized that new records could indicate either that previous range characterization failed to include pre-existing collection records further west or that C. maculata lengi has recently expanded its geographic range. To test these hypotheses, we searched several institutional insect collections and digital databases for records and found many earlier records of C. maculata lengi beyond its reputed geographic range, clearly showing that the previous characterization of its geographic distribution in North America was substantially underestimated. In addition, we report a new state record of C. maculata lengi from Wyoming, USA, that further indicates its geographic range expansion in North America. We discuss new records of C. maculata lengi in light of declines in native coccinelline lady beetle species in North America.

Annual Crops Contribute More Predators than Perennial Habitats during an Aphid Outbreak

Crops and semi-natural habitats provide predator populations with varying floral and prey resources, but their individual role on predator movement has seldom been studied. Here, we tease apart the role of adjacent habitats, predator abundance in the adjacent habitat, and soybean aphid (Aphis glycines Matsumura) abundance in soybean (Glycine max (L.) Merr.) on predator movement into soybean. We studied 12 soybean fields adjacent to alfalfa (Medicago sativa L.), canola (Brassica napus L.), spring wheat (Triticum aestivum L.), or woody vegetation, during a soybean aphid outbreak. Bidirectional Malaise traps and sticky traps were used to quantify predator movement between and abundance within soybean and adjacent habitats, respectively. Field plant counts were conducted to quantify aphid abundance in soybean. Coccinellidae and Syrphidae were the two most abundant families collected. Coccinellids and Eupeodes americanus (Wiedemann) (Diptera: Syrphidae) had net movement in soybean and their movement increased with aphid abundance. Movement of E. americanus was highest from wheat, coccinellid abundance was higher in wheat than woody vegetation, Toxomerus marginatus (Say) (Diptera: Syrphidae) abundance was highest in canola, and all other predators were more abundant in canola than woody vegetation. In general, our study suggests that annual crops have and provide more predators to soybean during aphid outbreaks than perennial habitats.

Intraguild Prey Served as Alternative Prey for Intraguild Predators in a Reciprocal Predator Guild between Neoseiulus barkeri and Scolothrips takahashii

The predatory mites Neoseiulus barkeri (Hughes) and the predatory thrips Scolothrips takahashii (Priesner) are known as potential biocontrol agents for the two-spotted spider mite Tetranychus urticae (Koch). These two predator species occur simultaneously on crops in agricultural ecosystems and are proved to be involved in life-stage specific intraguild predation. The intraguild prey may play a role in securing the persistence of the intraguild predators during food shortage periods. To understand the potential of intraguild prey as food source for intraguild predators in the N. barkeri and S. takahashii guild at low T. urticae densities, the survival, development and reproduction of both predators was determined when fed on heterospecific predators. The choice tests were conducted to determine the preference of the intraguild predator between the intraguild prey and the shared prey. Results showed that 53.3% N. barkeri and 60% S. takahashii juveniles successfully developed when fed on heterospecific predators. Female intraguild predators of both species fed on intraguild prey survived and laid eggs throughout the experiment. In the choice test, both intraguild predator species preferred their extraguild prey T. urticae. This study suggested that intraguild prey served as an alternative prey for intraguild predators prolonged survival and ensured the reproduction of intraguild predators during food shortage, ultimately decreasing the need for the continual release of the predators.

Coexistence between similar invaders: The case of two cosmopolitan exotic insects

Biological invasions are usually examined in the context of their impacts on native species. However, few studies have examined the dynamics between invaders when multiple exotic species successfully coexist in a novel environment. Yet, long-term coexistence of now established exotic species has been observed in North American lady beetle communities. Exotic lady beetles Harmonia axyridis and Coccinella septempunctata were introduced for biological control in agricultural systems and have since become dominant species within these communities. In this study, we investigated coexistence via spatial and temporal niche partitioning among H. axyridis and C. septempunctata using a 31-year data set from southwestern Michigan, USA. We found evidence of long-term coexistence through a combination of small-scale environmental, habitat, and seasonal mechanisms. Across years, H. axyridis and C. septempunctata experienced patterns of cyclical dominance likely related to yearly variation in temperature and precipitation. Within years, populations of C. septempunctata peaked early in the growing season at 550 degree days, while H. axyridis populations grew in the season until 1250 degree days and continued to have high activity after this point. C. septempunctata was generally most abundant in herbaceous crops, whereas H. axyridis did not display strong habitat preferences. These findings suggest that within this region H. axyridis has broader habitat and abiotic environmental preferences, whereas C. septempunctata thrives under more specific ecological conditions. These ecological differences have contributed to the continued coexistence of these two invaders. Understanding the mechanisms that allow for the coexistence of dominant exotic species contributes to native biodiversity conservation management of invaded ecosystems.

Establishment and Expansion of Harmonia axyridis Pallas (Coleoptera: Coccinellidae) in Urban Green Areas in the Iberian Peninsula: From 2015 to 2021

In the Western Palearctic region, Harmonia axyridis (Coleoptera: Coccinellidae) is mainly established in urban areas. In this study, we update its occurrence in urban areas of the Iberian Peninsula and determine its expansion after 2014. Changes in the ladybird species assemblage are also evaluated. We compile information about the records of H. axyridis in Spain from 2015 to 2021. In addition, we sample different locations to determine the relative abundances of the species composing the aphidophagous ladybird complex. The expansion of H. axyridis mainly occurred in Catalonia (Iberian Peninsula), where it is possible to identify two clear areas: one that has already been invaded and another that has not yet been invaded. Harmonia axyridis became the dominant species in the invaded area two years after it was first identified. This dominance is clearly shown on Liriodendron tulipifera and Tilia platyphyllos, where it accounted for more than 75% of the total collected individuals in the last year of the study. In the not-yet invaded area, Adalia bipunctata overcame Oenopia conglobata and became the prevalent species from 2020 onwards, likely due to its regular releases for aphid biocontrol. This study reveals that changes in ladybird species assemblages may not only be caused by invasive species, but also by biological control practices.

Potential displacement of the native Tenuisvalvae notata by the invasive Cryptolaemus montrouzieri in South America suggested by differences in climate suitability

Tenuisvalvae notata (Mulsant) (Coccinellidae) is a predatory ladybird beetle native to South America. It specializes in mealybugs prey (Pseudococcidae), but relatively little is known about its ecology. In contrast, the ladybird beetle Cryptolaemus montrouzieri Mulsant (Coccinellidae) is indigenous to Australia and has been introduced to many countries worldwide including Brazil for biological control of mealybugs. The potential impacts of these introductions to native coccinellids have rarely been considered. The software CLIMEX estimated the climate suitability for both species as reflected in the Ecoclimatic Index (EI). Much of South America, Africa, and Australia can be considered climatically suitable for both species, but in most cases, the climate is considerably more favorable for C. montrouzieri than T. notata, especially in South America. The CLIMEX model also suggests seasonal differences in growth conditions (e.g. rainfall and temperature) that could affect the phenology of both species. These models suggest that few locations in South America would be expected to provide T. notata climatic refugia from C. montrouzieri. Although other ecological factors will also be important, such as prey availability, this analysis suggests a strong potential for displacement of a native coccinellid throughout most of its range as a consequence of the invasion by an alien competitor.

Interactions Among Native and Non-Native Predatory Coccinellidae Influence Biological Control and Biodiversity

Over the past 30 yr, multiple species of predatory Coccinellidae, prominently Coccinella septempunctata L. and Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) have spread to new continents, influencing biodiversity and biological control. Here we review the mechanisms underlying these ecological interactions, focusing on multi-year field studies of native and non-native coccinellids and those using molecular and quantitative ecological methods. Field data from Asia show that H. axyridis, C. septempunctata, and Propylea japonica (Thunberg) (Coleoptera: Coccinellidae) are regularly among the most abundant predatory species but their rank varies by habitat. Studies of these species in their native Asian range, primarily related to their range in mainland China, document different patterns of seasonal abundance, species specific associations with prey, and habitat separation. Intraguild predation is well documented both in Asia and in newly invaded areas, and H. axyridis benefits most from this interaction. Harmonia axyridis also seems to rely more on cannibalism in times of prey scarcity than other species, and relatively sparse data indicate a lower predation pressure on it from natural enemies of coccinellids. Declines in the abundance of native coccinellids following the spread and increase of non-native species, documented in several multi-year studies on several continents, is a major concern for native biodiversity and the persistence of native coccinellid species. We suggest that future studies focus more attention on the community ecology of these invasive species in their native habitats.

Community science data suggests that urbanization and forest habitat loss threaten aphidophagous native lady beetles

Community scientists have illustrated rapid declines of several aphidophagous lady beetle (Coccinellidae) species. These declines coincide with the establishment of alien coccinellids. We established the Buckeye Lady Beetle Blitz program to measure the seasonal occupancy of coccinellids within gardens across a wide range of landscape contexts. Following the Habitat Compression Hypothesis, we predicted that gardens within agricultural landscapes would be alien-dominated, whereas captures of natives would be higher within landscapes encompassing a high concentration of natural habitat.Within the state of Ohio, USA, community scientists collected lady beetles for a 7-day period across 4 years in June and August using yellow sticky card traps. All identifications were verified by professional scientists and beetles were classified by three traits: status (alien or native), mean body length, and primary diet. We compared the relative abundance and diversity of coccinellids seasonally and determined if the distribution of beetles by size, status, and diet was related to landscape features.Alien species dominated the aphidophagous fauna. Native aphidophagous coccinellid abundance was positively correlated with forest habitat while alien species were more common when gardens were embedded within agricultural landscapes. Urbanization was negatively associated with both aphidophagous alien and native coccinellids. Synthesis and Applications: Our census of native coccinellid species within residential gardens-a widespread and understudied habitat-was enabled by volunteers. These data will serve as an important baseline to track future changes within coccinellid communities within this region. We found that native coccinellid species richness and native aphidophagous coccinellid abundance in gardens were positively associated with forest habitat at a landscape scale of 2 km. However, our understanding of when and why (overwintering, summer foraging, or both) forest habitats are important remains unclear. Our findings highlight the need to understand how declining aphidophagous native species utilize forest habitats as a conservation priority.

Long Term Monitoring in Switzerland Reveals That Adalia bipunctata Strongly Declines in Response to Harmonia axyridis Invasion

Simple Summary

The harlequin ladybird, Harmonia axyridis, is an Asian species that has invaded Europe and other continents, where it is suspected to cause the decline of native ladybirds through competition and predation. In north-western Switzerland, ladybirds were monitored for 11 years in four habitats (broadleaved hedges, meadows, pine and spruce stands) to assess the decline of native ladybirds following the invasion of the harlequin ladybird. These surveys showed that, on broadleaved hedges, the harlequin ladybird quickly became the most abundant species, representing 60–80% of all specimens collected in this habitat. One species, the two-spot ladybird, Adalia bipunctata, almost disappeared during this period, whereas it was the most abundant ladybird on broadleaved trees and shrubs when this study started. The other native species did not show any clear sign of decline. The harlequin ladybird was the second most abundant species in pine stands, and was not abundant in meadows and in spruce stands. The total number of ladybirds feeding on aphids did not decline during this period, suggesting that the arrival of the harlequin ladybird did not affect the predation pressure on aphids. Nevertheless, the severe decline of the two-spot ladybird deserves further investigations.

Abstract

A long-term monitoring was conducted at 40 sites in four different habitats in north-western Switzerland to observe changes in populations of native ladybirds, following the invasion of the Asian harlequin ladybird, Harmonia axyridis. From 2006 to 2017, the same trees and meadows were sampled at least seven times per year using standard protocols. On 15 broadleaved hedges, H. axyridis quickly became the dominant species, representing 60 to 80% of adult ladybirds collected. It was second in abundance at five pine (Pinus sylvestris) stands and was a minor component of the ladybird complex at five spruce (Picea abies) stands and in 15 meadows. This survey revealed the severe decline of Adalia bipunctata, which was the most abundant native ladybird on broadleaved trees in 2006–2009 and has almost disappeared since 2010. So far, other native ladybirds do not seem to decline significantly, including species occupying the same ecological niches as H. axyridis. The total number of aphidophagous ladybirds did not decline either, suggesting that the biological control function of ladybirds on aphids living in these habitats has not been affected by the arrival of H. axyridis. Recommendations are given to further assess the impact of H. axyridis on native ladybirds and aphids.

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.

History of the Biodiversity of Ladybirds (Coccinellidae) at the Black Sea Coast of the Russian Caucasus in the Last 120 Years-Does the Landscape Transformation and Establishment of Harmonia axyridis Have an Impact?

Studies of the history of regional insect fauna are important for understanding the changes in ecosystems. We analyzed the dynamics of ladybird fauna at the main sea resort of Russia over a period of 120 years to determine the following: (1) what species disappeared and what species appeared during landscape transformation; (2) what alien species introduced for pest control have been observed to date; and (3) whether the establishment of the global invader Harmonia axyridis (Coccinellidae) caused the extinction of some ladybird species in the Caucasus. We examined specimens collected by us and 54 other collectors including specimens from old museum collections and detected 62 species, 50 of which were collected in recent years (2011-2020). Landscape transformation and recreational use have caused not a decrease but an increase in ladybird biodiversity. Twenty-nine of 34 species recorded before 1930 have been observed in the region to date. Twenty-three other species have spontaneously spread to the region between 1930 and 2020 because of the creation of suitable anthropogenic habitats or because of unintentional introduction. Rodolia cardinalis, Cryptolaemus montrouzieri, Lindorus lophanthae, and Serangium montazerii were released for pest control, and they occur in gardens and streets but not in natural habitats. Harmonia axyridis, which appeared approximately 10 years ago, is abundant in urban and natural habitats, but there is no evidence that it caused the elimination of any ladybird species.

Interactions between exotic and native lady beetle species stabilize community abundance

A 23-year time-series of abundance for 13 lady beetle species (Coccinellidae) was used to investigate community stability. The community exhibited persistence in ten habitats, no overall trend in abundance, and low temporal variability quantified as Population variability (PV) = 0.33 on a scale from 0 to 1 that declined to 0.16 in the past 8 years. This high level of stability occurred as exotic lady beetles disrupted populations of the native species. For hypothetical communities of pairs of species (with randomly generated annual abundances in the range for lady beetles), PV increased linearly with the correlation coefficients between individual time series, illustrating a "portfolio effect". PV for the real community and the negative correlation between the abundance of exotics and natives fit this relationship precisely. A gradual decline of natives matched by an equal gradual rise in the abundance of exotics contributed to the negative correlation that stabilized the community. The abundance of the dominant species, an exotic, was negatively correlated with other exotics and most natives, and its stability increased over time, helping to stabilize the community. The community was most stable in habitats where beetle abundance was high (crops, particularly perennial crops) and, unexpectedly, was least stable in habitats with high diversity and stability of vegetation cover (forests). These data are consistent with the hypothesis that competition between exotic and native species, with release from competition for natives in some years, stabilized the abundance of this community. Stability may not last if populations of native species continue declining.

The Dynamic Shift Detector: An algorithm to identify changes in parameter values governing populations

Environmental factors interact with internal rules of population regulation, sometimes perturbing systems to alternate dynamics though changes in parameter values. Yet, pinpointing when such changes occur in naturally fluctuating populations is difficult. An algorithmic approach that can identify the timing and magnitude of parameter shifts would facilitate understanding of abrupt ecological transitions with potential to inform conservation and management of species. The “Dynamic Shift Detector” is an algorithm to identify changes in parameter values governing temporal fluctuations in populations with nonlinear dynamics. The algorithm examines population time series data for the presence, location, and magnitude of parameter shifts. It uses an iterative approach to fitting subsets of time series data, then ranks the fit of break point combinations using model selection, assigning a relative weight to each break. We examined the performance of the Dynamic Shift Detector with simulations and two case studies. Under low environmental/sampling noise, the break point sets selected by the Dynamic Shift Detector contained the true simulated breaks with 70–100% accuracy. The weighting tool generally assigned breaks intentionally placed in simulated data (i.e., true breaks) with weights averaging >0.8 and those due to sampling error (i.e., erroneous breaks) with weights averaging <0.2. In our case study examining an invasion process, the algorithm identified shifts in population cycling associated with variations in resource availability. The shifts identified for the conservation case study highlight a decline process that generally coincided with changing management practices affecting the availability of hostplant resources. When interpreted in the context of species biology, the Dynamic Shift Detector algorithm can aid management decisions and identify critical time periods related to species’ dynamics. In an era of rapid global change, such tools can provide key insights into the conditions under which population parameters, and their corresponding dynamics, can shift.

Populations naturally fluctuate in abundance, and the rules governing these fluctuations are a result of both internal (density dependent) and external (environmental) processes. For these reasons, pinpointing when changes in populations occur is difficult. In this study, we develop a novel break-point analysis tool for population time series data. Using a density dependent model to describe a population’s underlying dynamic process, our tool iterates through all possible break point combinations (i.e., abrupt changes in parameter values) and applies information-theoretic decision tools (i.e. Akaike's Information Criterion corrected for small sample sizes) to determine best fits. Here, we develop the approach, simulate data under a variety of conditions to demonstrate its utility, and apply the tool to two case studies: an invasion of multicolored Asian ladybeetle and declining monarch butterflies. The Dynamic Shift Detector algorithm identified parameter changes that correspond to known environmental change events in both case studies.

Insect Declines in the Anthropocene

Insect declines are being reported worldwide for flying, ground, and aquatic lineages. Most reports come from western and northern Europe, where the insect fauna is well-studied and there are considerable demographic data for many taxonomically disparate lineages. Additional cases of faunal losses have been noted from Asia, North America, the Arctic, the Neotropics, and elsewhere. While this review addresses both species loss and population declines, its emphasis is on the latter. Declines of abundant species can be especially worrisome, given that they anchor trophic interactions and shoulder many of the essential ecosystem services of their respective communities. A review of the factors believed to be responsible for observed collapses and those perceived to be especially threatening to insects form the core of this treatment. In addition to widely recognized threats to insect biodiversity, e.g., habitat destruction, agricultural intensification (including pesticide use), climate change, and invasive species, this assessment highlights a few less commonly considered factors such as atmospheric nitrification from the burning of fossil fuels and the effects of droughts and changing precipitation patterns. Because the geographic extent and magnitude of insect declines are largely unknown, there is an urgent need for monitoring efforts, especially across ecological gradients, which will help to identify important causal factors in declines. This review also considers the status of vertebrate insectivores, reporting bias, challenges inherent in collecting and interpreting insect demographic data, and cases of increasing insect abundance.

Differences in the Phenology of Harmonia axyridis (Coleoptera: Coccinellidae) and Native Coccinellids in Central Europe

Harmonia axyridis (Pallas), an invasive non-native species in central Europe, can outcompete other aphidophagous species. The distribution and abundance of H. axyridis vary depending on different host plants, and its effects on native coccinellid communities may change accordingly. The distribution and abundance of coccinellids in central Europe (50°N, 14°E) were investigated from 2010 to 2016. Coccinellids were counted at regular intervals on cereals (Avena, Hordeum, and Triticum), herbaceous plants (Matricaria and Urtica) and trees (Acer, Betula, and Tilia). Additionally, the occurrence over time of each species on these plants was assessed and used as an index of persistence. Across all years, the adults and larvae of H. axyridis were the dominant species of coccinellid on trees. However, H. axyridis was less abundant on herbaceous plants and cereals than on trees. Populations of native coccinellids and H. axyridis co-occurred on trees and persisted for the same length of time, while native coccinellids persisted longer than H. axyridis on herbaceous plants and cereals. Compared to 1976-1986, in the 2010s, the abundance of native species decreased on all plants by 50-70%. The presence of H. axyridis could be considered as a factor driving changes in the assemblages of native coccinellids.

Demographic histories of three predatory lady beetles reveal complex patterns of diversity and population size change in the United States

Predatory lady beetles (Coccinellidae) contribute to biological control of agricultural pests, however, multiple species frequently compete for similar resources in the same environment. Numerous studies have examined ecological interactions among the native North American convergent lady beetle (Hippodamia convergens) and two introduced species, the seven-spotted lady beetle (Coccinella septempunctata) and the Asian lady beetle (Harmonia axyridis), in agricultural fields and described multiyear population dynamics. However, the evolutionary dynamics of these interacting species of predatory beetles are uncharacterized. We utilize publicly available multilocus genotype data from geographically disjunct populations of these three species to estimate demography across North American populations. Coalescent analyses reveal (1) a recent (∼4-5 years) decline (>12 fold) in microsatellite effective population size of H. convergens, while expanding (mutation scaled growth rate in 1/u generations = 2910, SD = 362) over evolutionary time scales, (2) a massive (>150 fold), and very recent, effective population size decline in Ha. axyridis, and (3) population size growth (mutation scaled growth rate = 997, SD = 60) over recent and evolutionary time scales in C. septempunctata. Although these estimates are based on genetic data with different mutation rates and patterns of inheritance (mitochondrial versus nuclear), these dynamic and differing population size histories are striking. Further studies of the interactions of these predatory lady beetles in the field are thus warranted to explore the consequences of population size change and biological control activities for evolutionary trajectories in North America.

Response of the European Ladybird Adalia bipunctata and the Invasive Harmonia axyridis to a Neonicotinoid and a Reduced-Risk Insecticide

The spread of the multicolored Asian lady beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in Europe coincided with the decline of the native Adalia bipunctata (L.) (Coleoptera: Coccinellidae). Both species are predators of aphids in orchards, and differential susceptibility to insecticides used to control fruit pests may contribute to explain the competitive advantage of the invasive over the native species. In this study, the insecticidal activity of imidacloprid and spinetoram was tested on third instars and adults of both ladybird species under laboratory conditions. Insects were exposed to insecticide residues on potted peach plants that were sprayed with the maximum recommended field doses (100 mg/liter for imidacloprid and 66.67 mg/liter for spinetoram). Mortality was scored after short (2 d for both stages) and long (7 and 10 d for adults and larvae, respectively) exposure periods. The susceptibility to the insecticides was very similar for H. axyridis and A. bipunctata. Imidacloprid caused a significant increase in the mortality of both stages of the two species for every exposure period. On the other hand, when exposed to spinetoram residues, larvae and adults of both ladybirds did not show higher mortality than controls after short and long exposure periods. The pest suppression provided by ladybirds, which could be severely hampered by the applications of nonselective pesticides, might be enhanced by the adoption of reduced-risk insecticides, selective for these beneficial insects.

Heritable variation in prey defence provides refuge for subdominant predators

Generalist predators with broadly overlapping niches commonly coexist on seemingly identical sets of prey. Here, we provide empirical demonstration that predators can differentially exploit fine-grained niches generated by variable, heritable and selective defences within a single prey species. Some, but not all, clones of the aphid Aphis craccivora are toxic towards the dominant invasive predatory ladybeetle, Harmonia axyridis However, other less competitive ladybeetle species are not affected by the aphid's toxic trait. In laboratory and open field experiments, we show: (i) that subdominant ladybeetle species were able to exploit the toxic aphids, benefitting from the suppression of the dominant predator; and (ii) that this narrow-spectrum toxicity can function as an anti-predator defence for the aphid, but depends on enemy community context. Our results demonstrate that niche differentiation among generalist predators may hinge upon previously underappreciated heritable variation in prey defence, which, in turn, may promote diversity and stability of enemy communities invaded by a dominant predator.

Landscape simplification reduces classical biological control and crop yield

Agricultural intensification resulting in the simplification of agricultural landscapes is known to negatively impact the delivery of key ecosystem services such as the biological control of crop pests. Both conservation and classical biological control may be influenced by the landscape context in which they are deployed; yet studies examining the role of landscape structure in the establishment and success of introduced natural enemies and their interactions with native communities are lacking. In this study, we investigated the relationship between landscape simplification, classical and conservation biological control services and importantly, the outcome of these interactions for crop yield. We showed that agricultural simplification at the landscape scale is associated with an overall reduction in parasitism rates of crop pests. Additionally, only introduced parasitoids were identified, and no native parasitoids were found in crop habitat, irrespective of agricultural landscape simplification. Pest densities in the crop were lower in landscapes with greater proportions of semi-natural habitats. Furthermore, farms with less semi-natural cover in the landscape and consequently, higher pest numbers, had lower yields than farms in less agriculturally dominated landscapes. Our study demonstrates the importance of landscape scale agricultural simplification in mediating the success of biological control programs and highlights the potential risks to native natural enemies in classical biological control programs against native insects. Our results represent an important contribution to an understanding of the landscape-mediated impacts on crop yield that will be essential to implementing effective policies that simultaneously conserve biodiversity and ecosystem services.

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.

From effective biocontrol agent to successful invader: the harlequin ladybird (Harmonia axyridis) as an example of good ideas that could go wrong

The use of biological control agents to control pests is an alternative to pesticides and a tool to manage invasive alien species. However, biocontrol agents can themselves become invasive species under certain conditions. The harlequin ladybird (Harmonia axyridis) is a native Asian biocontrol agent that has become a successful invader. We reviewed articles containing “Harmonia axyridis” to gather information on its presence and surveyed entomologists researching Coccinellidae around the world to investigate further insights about the current distribution, vectors of introduction, habitat use and threats this species pose. The harlequin ladybird has established populations in at least 59 countries outside its native range. Twenty six percent of the surveyed scientists considered it a potential threat to native Coccinellidae. Published studies and scientists suggest Adalia bipunctata, native to Europe, is under the highest risk of population declines. Strict policies should be incorporated to prevent its arrival to non-invaded areas and to prevent further expansion range. Managing invasive species is a key priority to prevent biodiversity loss and promote ecosystem services.

Spatial and temporal changes in the abundance and compostion of ladybird (Coleoptera: Coccinellidae) communities

Because of their services to agriculture most ladybirds (Coleoptera: Coccinellidae) are intensively studied predators of mainly phytophagous pests. The study of the long-term variation in the composition of their communities was stimulated by recent dramatic changes in the abundance of some species. We review and evaluate possible effects of the main causes cited in the literature. Agricultural and habitat changes (particularly urbanization) affect coccinellid abundance, both negatively and positively. In the temperate zone dominant species occur most frequently associated with abundant prey populations on crops, weeds and planted stands of trees resulting from human activity. Invasive non-native species of coccinellids may endanger native species through intraguild predation or competition for resources, but their supposed serious negative effects on native species can differ considerably. Climatic change may influence coccinellid species in several ways, including indirect effects through lower trophic levels and desynchronisation of the phenologies of host plants, prey and coccinellid populations. In the near future we do not expect climate warming to have important effects on ladybird diversity globally, but local changes in the composition of coccinellid communities and abundance of particular species could occur.

Ecoinformatics (Big Data) for Agricultural Entomology: Pitfalls, Progress, and Promise

Ecoinformatics, as defined in this review, is the use of preexisting data sets to address questions in ecology. We provide the first review of ecoinformatics methods in agricultural entomology. Ecoinformatics methods have been used to address the full range of questions studied by agricultural entomologists, enabled by the special opportunities associated with data sets, nearly all of which have been observational, that are larger and more diverse and that embrace larger spatial and temporal scales than most experimental studies do. We argue that ecoinformatics research methods and traditional, experimental research methods have strengths and weaknesses that are largely complementary. We address the important interpretational challenges associated with observational data sets, highlight common pitfalls, and propose some best practices for researchers using these methods. Ecoinformatics methods hold great promise as a vehicle for capitalizing on the explosion of data emanating from farmers, researchers, and the public, as novel sampling and sensing techniques are developed and digital data sharing becomes more widespread.

Shifts in dynamic regime of an invasive lady beetle are linked to the invasion and insecticidal management of its prey

The spread and impact of invasive species may vary over time in relation to changes in the species itself, the biological community of which it is part, or external controls on the system. We investigate whether there have been changes in dynamic regimes over the last 20 years of two invasive species in the midwestern United States, the multicolored Asian lady beetle Harmonia axyridis and the soybean aphid Aphis glycines. We show by model selection that after its 1993 invasion into the American Midwest, the year-to-year population dynamics of H. axyridis were initially governed by a logistic rule supporting gradual rise to a stable carrying capacity. After invasion of the soybean aphid in 2000, food resources at the landscape level became abundant, supporting a higher year-to-year growth rate and a higher but unstable carrying capacity, with two-year cycles in both aphid and lady beetle abundance as a consequence. During 2005-2007, farmers in the Midwest progressively increased their use of insecticides for managing A. glycines, combining prophylactic seed treatment with curative spraying based on thresholds. This human intervention dramatically reduced the soybean aphid as a major food resource for H. axyridis at landscape level and corresponded to a reverse shift towards the original logistic rule for year-to-year dynamics. Thus, we document a short episode of major predator-prey fluctuations in an important agricultural system resulting from two biological invasions that were apparently damped by widespread insecticide use. Recent advances in development of plant resistance to A. glycines in soybeans may mitigate the need for pesticidal control and achieve the same stabilization of pest and predator populations at lower cost and environmental burden.