Prey capture performance in hatchlings of two sibling Harmonia ladybird species in relation to maternal investment through sibling cannibalism

1. To elucidate the factors responsible for the evolution of host specialisation, prey capture performance in hatchlings of two sibling ladybird species, Harmonia yedoensis and H. axyridis, feeding on four aphid species was examined. Harmonia yedoensis is a specialist predator that preys only on pine aphids in the field, whereas H. axyridis is a generalist predator with a broad prey range. 2. In H. yedoensis, sibling cannibalism in each clutch was intense and predation against pine aphid as well as other aphid species was moderately successful. In contrast, the predation success rate of H. axyridis against pine aphid was quite low. 3. Moreover, it was experimentally shown that increased maternal investment enhanced prey capture performance against pine aphid in H. yedoensis but not in H. axyridis hatchlings, despite their increased body size due to maternal investment. 4. In addition, morphological and behavioural analysis showed that hatchlings of H. yedoensis had longer legs and a larger head capsule size and could walk faster than H. axyridis. 5. In summary, the interactive effects between a large amount of maternal investment and morphological specialisation of the first instars may enable H. yedoensis to capture the pine aphid efficiently, a highly elusive prey for ladybird hatchlings. The ability of H. yedoensis to utilise the three other aphid species in addition to the pine aphid suggests that a trade‐off in prey capture performance is not the main factor in the host specialisation of H. yedoensis.     

Functional convergence and phenotypic divergence in two specialist species of pine-associated ladybirds

Traditionally, convergent evolution has been considered to produce phenotypic similarity in independently evolved species. By contrast, recent studies have detected morphological divergence between species even in similar selective environments when different morphological traits combine to produce a specific functional output. However, it is still unclear whether a complex combination of non-morphological phenotypic traits, such as behavioural and life-history traits, can produce a similar performance in different species. In this study, I examined prey capture performance and related phenotypes in two sympatric ladybird species, Sospita oblongoguttata and Harmonia yedoensis, which specialize on the giant pine aphid, which is known to be elusive for ladybird hatchlings. In particular, I focused on egg size and proportion of trophic eggs in the clutch, since the amount of maternal investment per offspring can contribute to prey capture performance of ladybird hatchlings. Predation success of hatchlings against the giant pine aphid was higher in both S. oblongoguttata and H. yedoensis than in Harmonia axyridis, a generalist ladybird species that feeds on various kinds of aphid species in nature. Sospita oblongoguttata females, however, produced relatively larger eggs and in most clutches provided no trophic eggs, whereas H. yedoensis females produced smaller eggs and provided more trophic eggs per clutch. Moreover, hatchling morphology in H. yedoensis more closely resembled that of its congener, H. axyridis, than that of the more distantly related S. oblongoguttata, although like H. yedoensis, S. oblongoguttata predates on the elusive pine aphid. These results in two pine-associated specialist ladybirds indicate that divergent phenotypes can nonetheless have similar prey capture performance. In conclusion, this work demonstrates that the general ultimate function can be achieved by various mechanisms through convergence that operates at different level of life.     

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

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

     

Habitat generalization of a predatory ladybird,Harmonia yedoensis (Coleoptera: Coccinellidae), in an allopatric area with respect to its sibling species Harmonia axyridis

In central Japan, Harmonia yedoensis is a specialist ladybird that is confined to pine tree habitats, whereas its sibling species Harmonia axyridis is a generalist that feeds on a wide range of aphid species in nature. Interestingly, H. axyridis is not distributed in the Ryukyu Archipelago, southern Japan. We hypothesized that the ecological niche of H. yedoensis should be wider in the Ryukyu Archipelago, where its competitor species in central Japan, H. axyridis, is absent. We undertook fieldwork and a survey of published works to examine habitat utilization by H. yedoensis in the Ryukyu Archipelago. We found that H. yedoensis adults in the Ryukyu Archipelago visited several kinds of deciduous trees, including wild tamarind, Chinese hibiscus, Taiwan cherry and Malayan banyan, as well as pine trees. These observations suggest that habitat generalization has occurred in H. yedoensis in the Ryukyu Archipelago, where it does not compete with H. axyridis.     

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.     

Asymmetric reproductive interference between specialist and generalist predatory ladybirds

1.?Closely related species often differ greatly in the quality and breadth of resources exploited, but the actual mechanisms causing these differences are poorly understood. Because in the laboratory specialized species often survive and perform as well or better on host species that are never utilized in nature, negative ecological interactions restricting host range must exist. Here, we focused on reproductive interference, which has been theoretically predicted to drive niche separation between closely related species with overlapping mating signals. 2.?We examined the interspecific sexual interactions in relation to ecological specialization and generalization in two sibling ladybird species, Harmonia yedoensis and Harmonia axyridis. Harmonia yedoensis is a specialist predator that preys only on pine aphids, which are highly elusive prey for ladybird hatchlings, whereas H.?axyridis is a generalist predator with a broad prey and habitat range. 3.?We experimentally showed that conspecific sperm fertilized the vast majority of eggs regardless of mating order (i.e. conspecific sperm precedence) when a female of H.?yedoensis or H.?axyridis mated with both a conspecific and a heterospecific male. Moreover, we demonstrated that mating opportunities of H.?yedoensis females strongly decreased as heterospecific density increased relative to conspecific density. In contrast, in H.?axyridis, female mating success was high regardless of conspecific or heterospecific density. 4.?Our results suggest that the generalist H.?axyridis should be dominant to the specialist H.?yedoensis in terms of reproductive interference. Our results support the hypothesis that asymmetric reproductive interference from the dominant species may force the non-dominant species to become a specialist predator that exclusively utilizes less preferred prey in nature.     

Intraguild predation of the aphid pathogenic fungus Pandora neoaphidis by the invasive coccinellid Harmonia axyridis

Abstract.  1. The ladybird Harmonia axyridis is an invasive alien species in many countries and is predicted to have a negative impact on native biodiversity. However, little is known on the status of this aphidophage as an intraguild predator of natural enemies of aphids such as insect-pathogenic fungi.
2. The study assessed the predation of the aphid-specific pathogenic fungus Pandora neoaphidis by adult and larval H. axyridis collected from the U.K. (an invasive population) and Japan (a native population) relative to that of the ladybird Coccinella septempunctata (native to the U.K.) and the non-U.K. C. septempunctata subspecies brucki that were either starved or unstarved.
3. Overall, predation of uninfected aphids was greater than infected aphids and, when given a choice, a preference for aphids was shown. However, the extent of this preference was dependent on the species and origin of the coccinellid. Harmonia axyridis (U.K.) consumed the greatest quantity of fungal cadavers and showed little preference for uninfected aphids over infected aphids. In contrast, C. septempunctata rarely consumed infected aphids. Life stage had no direct effects on predation but starved coccinellids consumed more uninfected aphids than infected aphids.
4.  Harmonia axyridis (U.K.) is a stronger intraguild predator of P. neoaphidis cadavers than the native species C. septempunctata and, therefore, may have an impact on the occurrence and persistence of P. neoaphidis . The differences in intraguild predation by H. axyridis collected in the U.K. and those from Japan suggests that individuals that invaded the U.K. could have a different genetic profile to those in its native range.     

Nutritional plasticity of the predatory ladybeetle Harmonia axyridis (Coleoptera: Coccinellidae): comparison between natural and substitution prey

The predatory coccinellid Harmonia axyridis is a polyphagous species, efficient at controlling certain aphid species and already commercialized in Europe for that purpose. The complete development of this predator can be accomplished using the aphid Acyrthosiphon pisum or Ephestia kuehniella eggs as substitution prey. Biochemical analyses were conducted on the proteins, lipids, and carbohydrates of these two different prey species. E. kuehniella eggs were 2 times richer in amino acids than A. pisum adults (12% of the fresh weight vs. 6%). E. kuehniella eggs were 3 times richer in lipids than the aphids but, on the contrary, the aphids were 1.5 times richer in glycogen. The impact of these two kinds of food on the body composition of the coccinellid was evaluated to appreciate the degree of nutritional plasticity of the coccinellid. The composition of the coccinellids feeding either on E. kuehniella eggs or on aphids was compared for amino acid, fatty acid and glycogen contents, revealing a good capability of H. axyridis to develop on foods that are very different in their biochemical composition. Nevertheless, when fed on aphids, the crude protein content of the predator was reduced and the lipid content decreased by a factor of two, with a change in amino and fatty acid patterns. Some biological parameters, such as larval mortality, adult weight, and fecundity, were modified according to the food eaten.     

Effect of cannibalism and predation on the larval performance of two ladybird beetles

The relative impact of cannibalism and predation on the development and survival of fourth instar larvae was assessed in two species of aphidophagous ladybird beetles, Coccinella septempunctata and Harmonia axyridis. The effect of eating aphids, conspecific larvae or heterospecific larvae on larval performance differed in the two species: aphids were the best food for C. septempunctata and survival of C. septempunctata larvae was significantly lower when offered heterospecific larvae rather than conspecific larvae or aphids as food, indicating that H. axyridis larvae were not suitable food for C. septempunctata. However, as the different foods did not affect the larval performance of H. axyridis, this species appears to be more polyphagous. Both intraguild predation by the aggressive larvae of H. axyridis and the polyphagous food habit of this species may account for its dominance in ladybird assemblages and its displacing other ladybird beetles in several places in the world.     

Negative dietary effects of Colorado potato beetle eggs for the larvae of native and introduced ladybird beetles

Aphidophagous ladybird beetles (Coleoptera: Coccinellidae) are attracted to and feed heavily on aphids, but many species will also feed opportunistically on other prey that they encounter. In potatoes (Solanum tuberosum L.) in Washington State, USA, coccinellids feed on both green peach aphids (“GPA,” Myzus persicae Sulzer) and eggs of the Colorado potato beetle (“CPB,” Leptinotarsa decemlineata Say). The guild of aphidophagous ladybirds includes two native species, Hippodamia convergens Guérin-Méneville and Coccinella transversoguttata Brown. Recently, an introduced species, Coccinella septempunctata L., has invaded and apparently displaced its native congener. A second exotic, Harmonia axyridis Pallas, has colonized the area and is becoming more abundant. We compared larval development of each species on a monotypic diet of GPA, a monotypic diet of CPB eggs, or a mixed diet of both GPA and CPB eggs. Our goal was to answer two questions: (1) do larvae of the four ladybird species benefit from including CPB eggs in their diet and (2) do the four ladybird species differ in their ability to utilize CPB eggs as prey? No larva of any species completed development on a pure diet of CPB eggs, and survivorship was highest for all species when they fed on a pure diet of GPA. One native species, H. convergens, and one exotic species, H. axyridis, exhibited significantly lower survivorship on a mixed diet of both CPB eggs and GPA, compared to a pure GPA diet; H. axyridis also took longer to develop from egg to adult when both prey were provided. Survivorship of the two Coccinella spp. was not altered by the inclusion of CPB eggs with GPA, although CPB eggs lengthened the development time of C. transversoguttata. Adult size was not consistently affected by diet for any of the coccinellids. Overall, no ladybird species benefited from the inclusion of potato beetle eggs in its diet. The two Coccinella species responded similarly to the inclusion of CPB eggs, and so we would not expect any difference in the success of coccinellid larval development in potato fields following the replacement of C. transversoguttata by C. septempunctata. Hippodamia convergens and H. axyridis, the two species whose survivorship was depressed by combining CPB egg and aphid prey, were also the two species that consumed the greatest number of CPB eggs during successful larval development. A comparison of total egg consumption by each species cohort suggested that displacement of the other species by H. axyridis would not alter CPB biological control, because the higher per capita feeding rate by H. axyridis larvae compensated for individuals’ greater mortality risk on a diet including CPB eggs.     

Increased nitrogen fertilization inhibits the biocontrol activity promoted by the intercropping partner plant

The examination of the compatibility between agricultural practices and biocontrol activities is crucial for establishing an efficient, eco-friendly, and sustainable pest management program. In this study, we examined the population dynamics of two specialist aphids, the English grain aphid (Sitobion avenae) on potted wheat and the pea aphid (Acyrthosiphon pisum) on potted alfalfa, as well as the biocontrol activity of a generalist predator, the harlequin ladybird beetle (Harmonia axyridis). We investigated their responses to the presence of the intercropping partner plant species (alfalfa and wheat, respectively) through plant volatiles or visual cues at three nitrogen fertilizer levels in a greenhouse. In the absence of the predator, the English grain aphid population growth rate increased significantly with increasing nitrogen levels, whereas the pea aphid population increased significantly more slowly in response to high nitrogen levels. The English grain aphid and pea aphid population dynamics were unaffected by the presence of the intercropping partner. However, the presence of the intercropping partner enhanced the control of both aphid populations by the harlequin ladybird beetle. Increasing nitrogen fertilizer levels decreased the predation rates, which were otherwise increased by the intercropping partner. The beneficial effects of the intercropping partner were eventually non-existent at the highest nitrogen level tested. These results imply that the interaction between the presence of intercropping partner and the nitrogen fertilizer application affects the biocontrol activity of the natural enemies of insect pests. Thus, the compatibility between agricultural intensification and biocontrol strategies in integrated pest management programs need to be investigated.     

Weak photoperiodic response facilitates the biological invasion of the harlequin ladybird Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)

Photoperiodic regulation of reproductive diapause in two invasive and two native populations of Harmonia axyridis and in one native population of Harmonia yedoensis was investigated in laboratory at 20°C, five photoperiods (day length of 10, 12, 14, 16 and 18 h) and two diets: (i) eggs of the Angoumois grain moth Sitotroga cerealella and (ii) the green peach aphid, Myzus persicae. Laboratory strains originated from native populations of H. axyridis from Irkutsk province of Siberia and H. yedoensis from South Korea showed a strong photoperiodic response: under short photoperiods (10–14 h and 10–12 h for H. axyridis and H. yedoensis, correspondingly), all females which fed on eggs and most of those fed on aphids did not start to lay eggs during 40 days after emergence, while under long photoperiods, all females fed on aphids and most of those fed on eggs oviposited. The photoperiodic response of H. axyridis from South Korea was less strong: on the both diets, the range of the photoperiodic response (the difference in the proportion of ovipositing females between the treatments with long and short days) was ca 40%. In the European (Czech Republic) and in the Caucasian (Sochi region, Russia) invasive populations of H. axyridis, the photoperiodic response was very weak: the proportion of females that started oviposition (when fed on aphids) or at least reproductive maturation (when fed on eggs) during 40 days after emergence was close to 100%, independently of the photoperiodic conditions. Obviously, instead of a rapid micro‐evolutionary adaptation of the critical day length to a new climate, the invasive populations of the harlequin ladybird decrease their dependence on photoperiod and thus the weak photoperiodic response of SE Asian population of H. axyridis can be considered as a pre‐adaptation further developed during the invasion.     

Effects of a larval antipredator response and larval diet on adult phenotype in an aposematic ladybird beetle

Many ladybird beetles respond to a potential predation event by `reflex bleeding' or secreting a noxious defensive chemical that is similar to hemolymph. Both adults and larvae show this response. Reflex bleeding is known to reduce predator attack rates and increase prey survival after an attack, especially when reflex bleeding is employed in combination with other cues such as odor and warning coloration. In this experiment, we examined how variability in the number of reflex bleeding events and food quality in the larval stage of the aposematic ladybird beetle Harmonia axyridis affected elytral color, development time, and terminal size in adults. Effects of reflex bleeding were subtle and may have been influenced by diet treatments. Adult color did not differ between bleed treatment groups but beetles that reflex bled tended to take longer to develop and grow to smaller sizes than control group beetles. There were clear and strong effects of larval diet on adult phenotype: an ad libitum pollen diet resulted in paler adult coloration, shorter development time, and larger adult size relative to a limited-availability aphid diet. Our results suggest that the best environment for producing bright-red coloration may not be the best environment for favorable expression of life history characters, especially under stressful conditions. Interactions between different life history stages of H. axyridis are also discussed. Received: 20 April 1997 / Accepted: 30 September 1997     

Genetic variation in larval period and pupal mass in an aphidophagous ladybird beetle (Harmonia axyridis) reared in different environments

Abstract Genetic trade‐offs for host plant use are hypothesized to facilitate the diversification of insect populations through specialization to their host plants. Previous studies mainly estimated the architecture of genetic variances and covariances in herbivorous species with discrete and limited types of host species. In contrast to herbivores, the relative abundance of resources for predatory species fluctuates in time and space, causing a more unpredictable encounter with prey species. The ecological characteristics of resource use might result in a differential mode of selection for herbivorous and predatory species, which could be reflected in a differential genetic architecture of developmental traits such as the duration of larval stage (henceforth referred to as larval period) and size of pupa (measured as pupal weight). This paper presents results from a study on the genetic architecture of larval period and pupal mass of an aphidophagous ladybird beetle, Harmonia axyridis Pallas, in different resource environments. Beetles reared on Acyrthosiphon pisum (Harris) showed a shorter developmental period and a heavier pupal mass than their siblings on Aphis craccivora Koch or on artificial diet, while the average larval period and pupal mass on A. craccivora and the artificial diet were similar. Further analyses of the genetic architecture suggest that the developmental traits on the two aphid species are genetically correlated, while there are only weak or no genetic correlations between these two traits on the two aphid preys and the artificial diet. Thus, the results suggest that the patterns of genotypic relationships between developmental traits differ from the phenotypic ones. The effects of past selection on the genetic architecture and the possible cause of the genetic correlation are discussed, as well as consequences for mass rearing for biological control.     

Weak responses to dietary enrichment in a specialized aphid predator

Some ladybeetles are specialist predators of aphids, coccids or other prey, although they often eat a variety of species from their focal prey taxon. In addition, the diet is often supplemented with alternative prey. How larvae of the aphidophagous Coccinella septempunctata L. utilize a non‐aphid alternative prey (fruit‐fly larvae Drosophila melonogaster Meigen) is compared with adequate (i.e. high‐quality) aphid prey provided alone (monotypic diet) or in mixed diets. The alternative prey are presented either nutrient‐enriched (i.e. raised on dog food supplemented medium) or not (raised on pure medium). Ladybird performance (survival, growth and development) is poor on the pure fly larvae diets, and also reduced when given mixed diets compared with the pure aphid diet. Nutrient enrichment of the fly larvae has no positive effects. The physiological background for the differences in food value, as indicated by performance in life‐history parameters, is a strong pre‐ingestive effect (i.e. reduced consumption of fly larvae compared with aphids) and a post‐ingestive effect (i.e. reduced utilization of assimilated larval fly tissue), whereas the assimilation efficiency of the consumed fly larvae is as high as that of aphids. The results show a physiological trade‐off resulting from prey specialization that reduces the possibility of utilizing alternative prey when the availability of aphids is scarce. Connected with this is a high robustness against variation in prey nutrient diversity and composition; the ladybird shows little positive response to dietary mixing (i.e. neither mixing of adequate aphids, nor of aphids and alternative prey) or to nutrient enrichment of prey. This contrasts with the results from generalist predators (spiders), where similar treatments lead to strong effects on life‐history parameters.     

Has the Attraction of Predatory Coccinellids to Cornicle Droplets Constrained Aphid Alarm Signaling Behavior?

When attacked by a predator, aphids of many species secrete cornicle droplets, containing an alarm pheromone, that results in the dispersal of nearby conspecifics. As females are parthenogenetic, alarm signaling functions to enhance the survival of clone-mates. Enigmatically, however, aphids are physically able to, but usually do not emit alarm pheromone when initially detecting a predator, but rather signal only when captured by a predator. We hypothesized that cornicle droplets may be attractive to natural enemies and result in an increased risk of predation for the signaler, thereby selecting for prudent alarm signalers. We tested this hypothesis by investigating the olfactory cues that the multicolored Asian ladybird beetle, Harmonia axyridis Pallas, uses to locate pea aphids, Acyrthosiphon pisum. In choice tests, H. axyridis were attracted to odors from pea aphid colonies, whether feeding or not feeding on a host plant leaf, but were not attracted to cornicle droplets containing alarm pheromone. Further, individual pea aphids emitting cornicle droplets were not located more often or in a shorter period of time by beetles than aphids not emitting cornicle droplets. Thus, the cost of emitting early alarm signals is not prohibitively high in regards to the attraction of predators such as H. axyridis.     

Toxicity of the aphid Aulacorthum magnoliae to the predator Harmonia axyridis (Coleoptera: Coccinellidae) and genetic variance in the assimilation of the toxic aphids in H. axyridis larvae

Larvae of the ladybird Harmonia axyridis are reported to suffer high mortality when they are fed with the aphid Aulacorthum magnoliae associated with the elder Sambucus sieboldiana. In the present study we first examined whether aphid toxicity to H. axyridis was altered when the aphids were reared on different host plants, and second whether some ladybird families could adapt specially to the toxic aphids. Ladybird larvae from each egg batch were divided into two groups; one group was fed with A. magnoliae reared on potato, and the other group was fed with A. magnoliae reared on elder. The ladybird larvae fed with elder aphids suffered significantly higher mortality and grew more slowly than did larvae fed with potato aphids. This result indicates that A. magnoliae aphids absorbed toxic substances or their precursors from S. sieboldiana. We suggest that host association of A. magnoliae with the primary host plant S. sieboldiana has been maintained because of the advantage of deterring predation. Significant and positive correlation was detected across H. axyridis sib families between the mean weight of larvae fed with elder aphids and the mean weight of larvae fed with potato aphids. The hypothesis that some ladybird families adapt specially to the toxic aphids was not supported. However, the available evidence showed that a large amount of genetic variance in performance is maintained in a wild population of the ladybird H. axyridis.     

Influence of aphid honeydew on the foraging behaviour of Hippodamia convergens larvae

1. Environmental cues associated with prey are known to increase predator foraging efficiency. Ladybird larvae are major predators of aphids. The sugary excretion of aphids (honeydew) has been proposed to serve as a prey‐associated cue for ladybird larvae. 2. Ladybird larvae are regularly found on the ground moving between plants or after falling off plants. The use of prey‐associated cues would be particularly beneficial for ladybird larvae on the ground in that such cues would help them to decide which plants to climb because aphids are patchily distributed within as well as amongst plants and, as a result, many plants are either not infested with aphids or do not host an aphid species of high nutritional value for ladybird larvae. 3. Laboratory experiments with larvae of Hippodamia convergens Guérin‐Méneville (Coleoptera: Coccinellidae) were carried out to explore whether honeydew accumulated on the ground is used as a foraging cue. The study also investigated whether, if honeydew is a foraging cue, larvae show differential responses to honeydew of high‐quality prey Acyrthosiphon pisum Harris compared with that of low‐quality prey Aphis fabae Scopoli (both: Homoptera: Aphididae). 4. Hippodamia convergens larvae stayed longer in areas containing honeydew but did not engage in longer bouts of searching. Furthermore, larvae did not distinguish between honeydew from high‐ and low‐quality aphid prey.     

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.     

Nitrogen fertiliser affects the functional response and prey consumption of Harmonia axyridis (Coleoptera: Coccinellidae) feeding on cereal aphids

Predator–prey interactions are influenced by nitrogen availability. Wheat (Triticum aestivum cv. Solstice) plants were provided with four levels of nitrogen and examined the responses of coccinellid predator, Harmonia axyridis to cereal aphids, Rhopalosiphum padi and Sitobion avenae. Increased nitrogen application improved nitrogen contents of the plants and also the body weight of cereal aphids feeding on them. In no‐choice feeding trials, H. axyridis consumed more aphids on low fertilised plants, suggesting a compensatory consumption to overcome reduced biomass (lower aphid size). Total biomass devoured by H. axyridis on all nitrogen fertiliser treatments was not statistically different. Logistic regression analysis of the proportion of prey consumed demonstrated that all developmental stages (larval and adult) of H. axyridis exhibited the type II functional response on all nitrogen fertiliser treatments. The rate of successful search (a′) of third and fourth instars and adults were the same across all fertiliser treatments suggesting that nitrogen fertilisation did not affect a′. Maximum handling time for the first instars of H. axyridis on R. padi (3.81 h^?1) and S. avenae (4.59 h^?1) was on the highest nitrogen treatment while minimum handling time was for the adults of H. axyridis on R. padi (0.20 h^?1) and S. avenae (0.20 h^?1) on the lowest nitrogen treatment. Handling time varied at varying fertiliser treatments within all instars and affected the predator's efficiency. The functional response curve, rate of successful search and handling time provide the information needed to understand the predator–prey interaction between H. axyridis and these cereals aphids. This could lead to the development of a better strategy for the biological control of R. padi and S. avenae at any particular level of nitrogen fertiliser regime in the field crops.