Influence of aphid–host plant pairs on the survivorship and development of the multicolored Asian ladybird beetle: implications for the management of vegetation in rural landscapes

Although the value of noncrop vegetation for biological control has been extensively studied in agricultural landscapes, there are few reports on how it functions mechanistically. When focusing on the pest control function provided by noncrop vegetation, tritrophic interactions among a predatory natural enemy, its prey, and the prey’s host plant need to be examined. In Japan, the multicolored Asian ladybird beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), an aphidophage, serves as a natural pest control agent in agricultural production, although the species’ introduction into Europe and North America for pest control has had a negative impact on native ecosystems. In the present study, 33 aphid–plant pairs from an agricultural landscape in the eastern Kanto region of Japan were examined experimentally for initial larval survivorship and development of H. axyridis. Significant differences were found among plant–aphid pairs with regard to these parameters. In addition, the larval survivorship of H. axyridis was not consistently determined by host plant or aphid species alone but was context-dependently influenced by the aphid–plant combination. Some alien host plants showed positive effects on the ladybird beetle. Others, however, served as hosts for unsuitable prey species, such as the competitive alien plants Solidago canadensis L. and Robinia pseudoacacia L., which are the host plants of Uroleucon nigrotuberculatum (Olive) and Aphis craccivora Koch, respectively. These findings suggest that various noncrop plants could be managed to promote ladybird beetle populations in rural landscapes.     

Importance of early arrival of adult <Emphasis Type="Italic">Harmonia axyridis</Emphasis> for control of <Emphasis Type="Italic">Aphis spiraecola</Emphasis> on apple

The biological control of aphid populations may only be possible when natural enemies arrive soon after aphid colonization. This study was done to identify how quickly adult Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) need to arrive at newly established spirea aphid [Aphis spiraecola Patch (Homoptera: Aphididae)] colonies on apple (Malus domestica Borkh.) to provide population control. A total of 100 newly established spirea aphid colonies were caged in an experimental apple orchard in West Virginia, USA. A single adult H. axyridis was added to each of ten caged colonies at day 0, 5, 10, 15 and 20 days after caging. An additional ten caged colonies were opened for exposure to natural levels of predation at each of the treatment intervals as a control. The single H. axyridis eliminated the aphid colonies significantly more quickly than natural predation for up to ten days after colony establishment. The probability of an aphid colony producing alates was significantly lower in the presence of a single H. axyridis adult than when exposed to natural predation for the first ten days. Adult H. axyridis beetles are capable of completely controlling individual spirea aphid colonies on apple only if they are abundant enough to find colonies within one week of colony establishment.     

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

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

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.     

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.     

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.     

Alterations in foraging behavior of Coccinella septempunctata and Propylea japonica mediated by a novel defended prey affect their predatory potential

Generalist aphidophagous coccinellids have to cope with novel prey aphids in environments that are changing rapidly because of anthropogenic activity. The goldenrod aphid, Uroleucon nigrotuberculatum (Olive) (Hemiptera: Aphididae), is a noxious prey, which was recently introduced into Japan. It is a major prey for the native Japanese predators Coccinella septempunctata bruckii Mulsant and Propylea japonica (Thunberg) (both Coleoptera: Coccinellidae) in early summer on patches of solidago, Solidago altissima L. (Asteraceae). Prey preference of these coccinellids between this aphid and a native suitable prey aphid, Megoura crassicauda Mordvilko (Hemiptera: Aphididae), as well as their foraging behavior were studied for a better understanding of the negative impacts of the noxious novel aphid. Coccinella septempunctata initially preferred the novel prey, but later switched to the native prey, M. crassicauda; P. japonica had no preference for either prey. Feeding time of the first instars of C. septempunctata on U. nigrotuberculatum was significantly longer than that of P. japonica. The foraging bouts of fourth instars of C. septempunctata were significantly longer on U. nigrotuberculatum than on M. crassicauda, whereas only the feeding time of fourth instars of P. japonica on U. nigrotuberculatum was significantly longer than on M. crassicauda. Both coccinellids consumed less of U. nigrotuberculatum than of M. crassicauda. Thus, solidago patches infested by U. nigrotuberculatum may present an ecological trap, especially for C. septempunctata.     

Impact of plant architecture and extraguild prey density on intraguild predation in an agroecosystem

Several models and experimental studies conducted in confined environments have shown that intraguild predation (IGP) can modulate population abundances and structure communities. A number of ecological and abiotic factors determine the nature and frequency of IGP. This study examined the effect of plant architecture and extraguild prey density, and their interactions, on the occurrence of IGP between two species of ladybird, Harmonia axyridis (Pallas) and Propylea quatuordecimpunctata L. (both Coleoptera: Coccinellidae). Theoretical concepts predict that IGP levels would increase with a decrease of both extraguild prey density and plant structural complexity. We conducted a factorial experiment in an open soybean field into which coccinellid larvae were introduced in experimental plots for a period of 5 days. We tested two levels of soybean aphid [Aphis glycines Matsumara (Hemiptera: Aphididae)] density, low and high (100 and 1 000 aphids per plot, respectively), and two levels of plant complexity, low (by removing half of the branches from the soybean plants) and high (by leaving plants intact). We used species‐specific molecular markers to detect the presence of P. quatuordecimpunctata in the digestive tract of H. axyridis. Molecular gut‐content analysis of H. axyridis revealed that rates of IGP were higher (20%) at low aphid density than at high aphid density (<6%). Decreased plant complexity did not impact the frequency of IGP. In accordance with existing literature, this study demonstrates that IGP is amplified at low extraguild prey density. We conclude that considering environmental factors, such as extraguild prey density, is crucial to improve our ability to predict the impact of intraguild predation on community structure and, from an applied perspective, biological control.     

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.     

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.     

Consumption patterns of the multicolored Asian ladybird Harmonia axyridis on the broad bean aphid Aphis craccivora

The multicolored Asian ladybird Harmonia axyridis Pallas is often used as a biological control agent against Aphis craccivora Koch, a key pest aphid of broad bean. Understanding consumption characteristics of biological control agents is critical for developing effective biological control programs. Here, under laboratory conditions we studied consumption patterns of H. axyridis on A. craccivora including functional response and intraspecific competition. All larvae (1st-, 2nd-, 3rd-, 4th-instar) and adults (male and female) of H. axyridis exhibited a Type II functional response to A. craccivora. We found H. axyridis females were superior to individuals of other developmental stages, based on three key parameters in functional response model, i.e. attack rate (a = 90.0%), handling time (T_h = 2.7 min), and consumption threshold (N_max = 526.7 individuals). Results from our analysis of intraspecific competition showed that when attacking A. craccivora, 4th-instar larvae of H. axyridis suffered from the greatest intraspecific competition (coefficient of mutual interference, m = 0.48). Our results show that 4th-instar larvae and adults of H. axyridis are most effective in controlling A. craccivora, and proper density of H. axyridis released will reduce intraspecific competition. This analysis reveals both prey-predator and predator-predator interactions, and highlights the value of biological control in reducing pesticide use and protecting ecological environments.     

Suppression of aphids by augmentative release of larvae of flightless Harmonia axyridis

The release of the larvae of flightless ladybird beetles could extend the duration of effective control because of the longer presence of adult stages, and the per individual production cost for juvenile stages is lower than that for adult stages. A preliminary release experiment was conducted to assess the effectiveness in controlling two aphid species, Aphis gossypii and Aulacorthum solani, using second instars of a flightless strain of Harmonia axyridis. The number of A. gossypii was suppressed in greenhouses that contained the flightless strain compared with greenhouses that contained the wild‐type strain. In one of two replicates, more flightless adults were observed on the plants for longer than wild‐type adults. However, it was not clear whether the extension of the residence period contributed to the effectiveness in controlling aphids directly, because the population of ladybirds in the greenhouses consisted of both larvae and adults during parts of the experimental period. In flightless H. axyridis, the release of larvae was more effective in suppressing A. solani than the release of adults. These results suggest that it may be more effective to release larvae of flightless H. axyridis than wild‐type larvae or flightless adults.     

Possible coexistence of Harmonia axyridis Pallas (Coleoptera: Coccinellidae) and Diaeretiella rapae M'Intosh (Hymenoptera: Braconidae) in the biological control of Lipaphis erysimi (Homoptera: Aphididae)

To study the interactions between the aphidophagous predator Harmonia axyridis Pallas (Coleoptera: Coccinellidae) and the specialist aphid parasitoid Diaeretiella rapae M'Intosh (Hymenoptera: Braconidae) in the biological control of mustard aphid, Lipaphis erysimi (Homoptera: Aphididae), the prey discrimination by H. axyridis among unparasitized, non-mummified parasitized and mummified aphids was examined under laboratory conditions. Prey/host selections were also tested by offering L. erysimi at various developmental stages to assess the possibility of coexistence between the two species, so the prey preference of H. axyridis when D. rapae parasitize aphids, and the host preference of D. rapae when H. axyridis interfered with the parasitization were detected. We found that H. axyridis could discriminate against mummies rather than non-mummified parasitized aphids. The ladybug showed a significantly positive preference for adult prey when D. rapae turned aphids into mummies, while D. rapae tended to parasitize younger nymphal aphids when H. axyridis was introduced. The present study suggests the prey discrimination against mummies by H. axyridis, and indicates that H. axyridis and D. rapae can avoid resource competition by attacking different and non-overlapping developmental stages of aphid. Thus, H. axyridis and D. rapae can potentially coexist and establish a stable ecosystem in the biological control of L. erysimi.     

Effect of different diets on the growth and development of Harmonia axyridis (Pallas)

Harmonia axyridis (Pallas) is an important natural enemy of crop pests. Feeding H. axyridis through artificial diets (ADs) is an important means to achieve large-scale production. In this study, the effects of different diets on the growth, development and reproduction of H. axyridis were comprehensively evaluated, and the reasons for the reduced reproductive capacity of H. axyridis fed ADs were preliminarily explored. Artificial diets were prepared using pig liver and pork as the main ingredients. Larval duration, larval survival rate, egg production and other traits were comprehensively evaluated. Harmonia axyridis fed ADs during both the larval and adult periods completed growth and development from larva to adult but had a prolonged development duration (6.13-day extension) and reduced survival rate (15.3% reduction) in the larval stage. In addition, adults could not lay eggs. Next, individuals of H. axyridis were fed Megoura japonica (Matsumura) in the larval stage and an AD, adequate aphids (AA) or an artificial diet plus 5 (AD5), 10 (AD10) or 25 (AD25) aphids in the adult stage. The adults in the AD group produced a small number of eggs (103.3 eggs). When aphids were added to the diet, egg production gradually increased with the number of aphids added. The AD25 group exhibited no significant difference in egg production compared with that in the AA group (983.8 eggs and 1,158.3 eggs, respectively). Anatomical observations of the H. axyridis adults in these five groups revealed that ovary development was slowest in the AD group. In addition, we found that the levels of vitellogenin and juvenile hormone were significantly lower in the AD group than in the AA group. These results provide a foundation for formulating ADs for H. axyridis and improving the large-scale reproduction of this species.     

Direct and indirect effect of cannibalism and intraguild predation in the two sibling Harmonia ladybird beetles

In this study, we focused on the direct (i.e., predation) and indirect (i.e., potential threat from coexisting with a larger individual) effects of cannibalism and intraguild predation (IGP) during larval stages of two sibling ladybird beetles. These effects play an important role in the coexistence of the generalist–common Harmonia axyridis and specialist–rare H. yedoensis (Coleoptera: Coccinellidae). Direct predation effect of cannibalism and IGP was asymmetric in the two sibling ladybird beetles; the fourth instar larvae of H. axyridis were better intraguild predators than cannibals, while the reverse was true in the larvae of H. yedoensis. Neither cannibalism nor IGP significantly affected female body weight in either species. Larval H. axyridis surviving exposure to cannibalism or IGP had a reduced number of ovarioles as adults, whereas adult H. yedoensis ovarioles were not affected. For the indirect effects, longer developmental times in males and females and a lower total number of ovarioles in females were detected in H. axyridis. In H. yedoensis, shorter developmental time of males, lighter adult weight and fewer total ovarioles in females were observed. Olfactometer choice experiments clarified that the fourth instar larvae of H. axyridis avoided the first instar conspecific larvae, while those of H. yedoensis were attracted to the odors from H. axyridis and conspecifics. Thus, H. axyridis has an avoidance mechanism only for cannibalism but not for IGP, whereas H. yedoensis does not have any avoidance mechanism. These different behaviors in the direct and indirect effects of cannibalism and IGP observed in the laboratory may play important roles in the coexistence of generalist–common H. axyridis and specialist–rare H. yedoensis in natural conditions, compensating for the large handicap of H. yedoensis at reproductive interference from H. axyridis.     

Pea aphid dropping behavior diminishes foraging efficiency of a predatory ladybeetle

Antipredator defensive behaviors are a well‐studied and often crucial part of prey life histories, but little has been done to quantify how such behaviors affect natural enemies, their foraging, and their effectiveness as biological control agents. We explored how the generalist predatory coccinellid Harmonia axyridis Pallas (Coleoptera: Coccinellidae) affects the dropping behavior of the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), and in turn, how that defensive behavior affects the foraging efficiency of the predator. Experimental arenas that allowed or prevented pea aphid dropping were compared to determine how dropping influences the foraging of multiple life stages of H. axyridis: second instars, fourth instars, and adults. Dropping reduced predation on aphids by all ladybeetle life stages. Despite older predators inducing more dropping, aphid dropping reduced predation by approximately 40% across all ladybeetle life stages. Aphid dropping and predator consumption of aphids were both correlated with how much the predator moved, which also increased with predator life stage. We suggest that the high rates of dropping induced by H. axyridis and the subsequent decrease in H. axyridis foraging efficiency may partially explain why H. axyridis is less effective at controlling pea aphids than it is at controlling other aphid species that do not drop.     

Cannibalism and interspecific predation in two predatory ladybirds in relation to prey abundance in the field

Life tables for two predatory ladybirds,Coccinella septempunctata andHarmonia axyridis, were constructed in two years in which prey abundance differed. The prey aphid,Aphis gossypii, was abundant on its primary host from late May to late June. Females ofH. axyridis andC. septempumctata laid their eggs during the increase and peak in aphid abundance. The oviposition period ofC. septempunctata started before and was shorter than that ofH. axyridis. In both species, intraguild predation and/or cannibalism of the egg and fourth instar stages, but rarely of other developmental stages, were observed. Fourth instar larvae ofH. axyridis had to complete their development when aphids were scarce more frequently than those ofC. septempunctata. The highest frequency of intra- and interspecific predation was of fourth instarH. axyridis larvae. In terms of intraguild predation, the larvae ofH. axyridis preyed on larvae ofC. septempunctata, but the reverse was not observed. Percentage survival from egg to adult inH. axyridis was higher than inC. septempunctata in both years, and least in both species in the year of low aphid abundance. These results suggest that prey abundance influenced the frequency of cannibalism and intraguild predation, which were important in structuring this guild of ladybirds.     

Interaction between Podisus maculiventris and Harmonia axyridis two predators used in augmentative biological control in greenhouse crops

Intraguild predation (IGP) betweenthe pentatomid Podisus maculiventris(Say) and the coccinellid Harmoniaaxyridis (Pallas) in the absence or presenceof the extraguild prey Spodopteralittoralis (Boisduval) and Myzuspersicae (Sulzer) was studied in thelaboratory. Interactions were asymmetric infavor of the pentatomid. Podisusmaculiventris readily fed upon eggs and larvaeof H. axyridis, but adult beetles wererarely attacked. Success of attacks by P.maculiventris was stage dependent, fourthinstars and adults being more successful inkilling ladybeetle larvae than second instars.Attacks by H. axyridis on the pentatomidwere rare and none of them were successful. Theeffect of introducing extraguild prey on thelevel of IGP was tested both in petri dishesand on caged sweet pepper plants. Whensufficient numbers of S. littoralislarvae were present to satiate the pentatomid,predation on H. axyridis larvae decreasedsignificantly, indicating that the coccinellidis a less preferred or less vulnerable prey.When the aphid M. persicae was presentedas extraguild prey, levels of IGP were notaltered. Nymphs of P. maculiventrissuccessfully completed development whenexclusively fed on larvae of H. axyridis,but developmental time was longer than onlepidopteran prey. No pentatomid nymphs reachedadulthood on aphids alone. IGP by P.maculiventris on H. axyridis may be ofsome importance in greenhouse crops, where bothpredators are being used increasingly inaugmentative biological control programs.Nonetheless, it is expected that in practicelarger larvae and adults of H. axyridiswill escape most attacks by the pentatomid.     

Pollen as an alternative food for Harmonia axyridis

The current study examines the potential of the multicoloured Asian lady beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) to use pollen as a food to sustain development and reproduction in the absence of insect prey. Three populations of H. axyridis were used in this study: a long-term laboratory population (since 1998) and a melanic and non-melanic population originating from field collected individuals in Belgium. The insects were allowed to develop and reproduce on frozen eggs of Ephestia kuehniella Zeller (Lepidoptera: Phycitidae), frozen moist bee pollen or an even mixture of the two. Females of the field population offered the mixed diet initiated oviposition sooner than those fed only E. kuehniella eggs, but other developmental and reproductive traits were similar on these diets. A diet of pollen alone allowed 35–48% of the larvae of the field population of H. axyridis to successfully reach adulthood. However, developmental time for these individuals was prolonged by 31–49% and adult body weight was reduced by 37–68%, compared to individuals offered the diets containing E. kuehniella eggs. When fed exclusively on pollen in their larval and adult life, about 40% of the adult females of either field population were able to produce a small number of viable eggs. The laboratory and field strains differed in their response to diet for a number of developmental and reproductive traits. The exploitation of pollen and other plant foods at times when insect prey is scarce, may offer a further competitive advantage to the non-indigenous coccinellid H. axyridis over native European predatory lady beetles that share the same niche and are less capable of using pollen as an alternative food.     

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.