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There is a lot of information on the factors limiting the distributions of species in their native areas, but much less on those limiting potential changes in distributions of species that are currently spreading outside their present range, especially invasive species. However, this information is often quite essential, as it enables the prediction of future spatial distributions and local abundances of invasive species and the potential effect they may have on people and crops. Arising from glasshouse escapes in North America and the Netherlands, the invasive ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), originally from the east Palearctic, has now spread across the whole of North America and most of Europe, both of which caused serious concern. Recent observations show that the spread of H. axyridis towards the equator is limited. For example, it is quite rare in the Mediterranean area and its northward spread in South America is also quite slow, as if there was something limiting its spread towards the equator. European literature indicates it is neither climate, nor the distance of the Mediterranean from the original release location in the Netherlands. Therefore, we hypothesized that it may be biotic factors. In particular, the duration of colonies of prey (colony is the set of individuals in one patch, usually on one plant) that becomes shorter as one approaches the equator. This may lower the fitness of the predator and subsequently lead to low population densities. We test here, whether the duration of aphid colonies is shorter in the Mediterranean area than in Central Europe. Unfortunately, our data does not support this hypothesis. Therefore, the question of what limits the distribution of H. axyridis towards the equator remains to be resolved.

In Central Europe, the most abundant aphid infesting the leaves of small grain cereals is Metopolophium dirhodum (Walker) (Homoptera: Aphididae). Annual variation in its seasonal dynamics was evaluated using a 25-yr series of standardized weekly censuses of winter wheat plots. M. dirhodum made up >50 % of the aphids on the foliage. Date of immigration (8 May-3 July), length of period of population increase (0-9 wk), and date of attaining maximum abundance (28 May-22 July) varied greatly. For the prediction, we regressed maximum numbers/tiller on numbers recorded in the first week after heading. The regression of maximum abundance on nonzero aphid counts revealed a critical number of ≥1.50 aphids/tiller, which if exceeded resulted in a harmful maximum abundance of ≥10 aphids/tiller at the peak. Zero aphid counts resulted in 10% of cases with a harmful maximum abundance. Using this regression for prediction will result in 18% of the recorded cases being false negatives and 9% false positives. Parallel annual variation in the average maximum numbers of M. dirhodum, Sitobion avenae (Fabricius) (Homoptera: Aphididae), and Rhopalosiphum padi (Linné) (Homoptera: Aphididae) indicated the following factors that affected their abundance: temperature in winter and host plant quality. The predictions apply only in areas where M. dirhodum is holocyclic and aphids do not overwinter in wheat stands., (© The Author(s) 2018. Published by Oxford University Press on behalf of Entomological Society of America.)

The numbers per tiller (abundance) and per unit area of ground (population density) of the dominant cereal aphids in winter wheat crops, Sitobion avenae (Fabricius) and Metopolophium dirhodum (Walker) (Hemiptera: Aphididae) were recorded from 2000–2015. The results were used to test the hypothesis that at the population peak and 4 weeks previously, the population density of aphids in winter wheat crops (Triticum aestivum L., Poaceae) is uniformly distributed with respect to surface area and, as a result, their abundance is high in sparse stands (SPA) where the colonizing aphids are scattered among a small number of tillers (ca. 80 m−2), and low in dense stands (DEN) where they are scattered among a larger number of tillers (ca. 440 m−2). This prediction was verified for S. avenae, the population density of which did not significantly differ between SPA and DEN stands throughout this period. This species feeds mainly on the ears, whose nutritional quality for aphids varies little with crop density and during the course of ripening. In contrast and contrary to our prediction, the population density of M. dirhodum increased throughout this period more rapidly in SPA than in DEN stands. This species lives on leaves whose quality is better and remain present for longer during the course of ripening of the crop in SPA than DEN stands. The abundance of both species was higher in SPA than in DEN stands. Greater direct damage to cereal crops can be expected when using technologies and cultivars of winter wheat that need to be planted sparsely. [ABSTRACT FROM AUTHOR]

The balance between risk and benefit of exploiting resources drives life‐history evolution in organisms. Predators are naturally recognized as major drivers of the life‐history evolution of their prey. Although prey may also influence the life‐history evolution of their predators in the context of an evolutionary arms race, there is far more evidence of the role of predators than of prey.The goal of this study was to investigate the role of prey in life‐history evolution of predators using ladybird beetle predators of aphids and coccids. These particular ladybirds and their prey were chosen because literature shows that the pace of life of aphids is faster than that of coccids and this difference is reflected in the life histories of the ladybirds that specialize on feeding on aphids or coccids.Thirty‐four species of ladybird predators of aphids and eight of coccids belonging to five different tribes were collected and reared in the laboratory. The females were weighed as well as their eggs, and their reproductive investment estimated as the number of ovarioles. Phylogenetic relatedness was controlled for in the statistical analyses.Controlling for female mass revealed that ladybird predators of aphids lay bigger eggs than ladybird predators of coccids. This difference is not influenced by phylogenetic relatedness but only by the type of prey eaten. We suggest that ladybird predators of coccids lay smaller eggs because neonate larvae do not have to search, catch, and subdue prey. Both types of ladybirds have a similar reproductive investment relative to their body mass when phylogeny is controlled for.Recognizing the influence of prey on the life‐history evolution of predators is important for understanding food web dynamics. From an applied perspective, this fine evolutionary tuning of prey–predator relationships should be used to guide and increase the efficiency of biological control programs. [ABSTRACT FROM AUTHOR]

Population dynamics of a predator-prey system is usually simulated by the classical Lotka-Volterra models, which were successfully applied to the population dynamics of snowshoe hare and lynx and many other predator-prey systems. Attempts were made to apply them also to insect predator-prey systems, but in terms of biological control, they did not reveal the features of the predators that control the abundance of their prey. The most conspicuous example of failure of Lotka-Volterra models applied to insect predator-prey systems are ladybird-aphid systems, in which these models usually fail to fit empirical data. Because of their practical importance and because they are very well studied, we have chosen aphid-ladybird systems as a model. We summarize the results published on various aspects of the population dynamics of aphid-ladybird systems and present them in the context of empirical data. Using new data, we more closely specify the existing metapopulation model of aphid-ladybird interactions. Based on the arguments presented here, we conclude that the ladybird-aphid case can be generalized to insect (and maybe even other) predator-prey systems, where the ratio of the generation times of the predator to that of the prey (GTR) is large. In such systems, the main selection pressure on predators is choosing the best strategy to maximize survival of their offspring, rather than on maximization of the amount of prey eaten. Thus voracity, which is the main determinant of population dynamics in Lotka-Volterra models, loses its role and is replaced by optimization of the choice of oviposition sites in systems with large GTRs. [ABSTRACT FROM AUTHOR]

3 Brown, P.M.J. & Roy, H.E. (2017) Native ladybird decline caused by the invasive harlequin ladybird Harmonia axyridis: evidence from a long-term field study. Thus, I decline in percentage abundance does not necessarily indicate a negative effect of the invader on the abundance of the native species i , as is often claimed (Alyokhin & Sewell, 2004; Grez I et al i ., 2016; Brown & Roy, 2017, etc.). It is seductive to say that an invader in reducing the abundance of native predators lowers the biocontrol potential of the whole guild (Soares I et al i ., 2008; Brown I et al i ., 2011; Roy I et al i ., 2012). [Extracted from the article]

Modelling of empirical data on the abundance of host-specific, tree-dwelling aphids indicates that their abundance is determined by the effect of the abundance of their host plants on the realised annual population growth rate ( I R i ) of the aphids (Dixon & Kindlmann, [7]). Viewed in this way it is not just the abundance of the host plant of aphids that determines the abundance of aphids (Dixon & Kindlmann, [7]) but also their potential annual population growth rate ( I r i SB p sb ) and subsequently their realised population growth rate ( I R i ). The most striking and consistent feature of rare aphid species is that the period suitable for their development and reproduction is shorter than for the common species and, consequently, the potential yearly rate of increase of these rare species is lower. [Extracted from the article]

In this study we analyzed data in the literature on the rates of development of parasitoids that parasitize aphids and coccids. The objective was to determine whether their rates of development, as is well documented for ladybirds, are also dependent on that of their prey. The analysis revealed that, like ladybirds, parasitoids that parasitize aphids develop faster than those that parasitize coccids. Parasitoids and ladybird predators show the same pattern in their rates of development: those attacking aphids develop faster than those attacking coccids. This is strong evidence that we are dealing with a general response rather than one specific to ladybirds. It also lends support to the concept that the development rates of these natural enemies are evolutionarily conserved rather than phylogenetically constrained. [ABSTRACT FROM AUTHOR]

The hypothesis that small species of aphidophagous coccinellids need lower aphid population densities for reproduction than large species (Dixon, 2007) was tested in the field. In 2006 we compared seasonal changes in the oviposition behaviour of two coccinellid species regularly found in cereal stands in central Europe, the large Coccinella septempunctata L. and the small Propylea quatuordecimpunctata (L.). Adults of both species were collected at 2-3 day intervals from stands of winter wheat and spring barley, females were allowed to deposit eggs for 24 h following collection and the percentage that laid eggs and the number of eggs were recorded. Both species colonized the cereal crop simultaneously in the middle of May. After colonization of the crop, while the aphid density was still low, few females of C. septempunctata oviposited and laid only a few eggs. Oviposition increased up to a maximum c. 1 month later and was closely associated with prey abundance. Of the females of P. quatuordecimpunctata, whose mass is about one quarter of that of the former species, the percentage ovipositing and number of eggs laid varied less in time and was less associated with prey abundance than in C. septempunctata. As predicted by theory, the small P. quatuordecimpunctata was more effective at exploiting the lower prey densities as it produced proportionally more of its eggs during the early stages of the aphid infestation than the larger C. septempunctata. [ABSTRACT FROM AUTHOR]

To test the predictions of allometric analyses of laboratory data on aphidophagous ladybirds, a study was carried out on a small [ Propylea quatuordecimpunctata (L.); dry female body mass 3.7 mg] and large species ( Coccinella septempunctata L.; 15.4 mg) (both Coleoptera: Coccinellidae) of predatory ladybird, which regularly exploit cereal aphids. In 2003–2006, females of C. septempunctata and in 2006 P. quatuordecimpunctata were collected at 2- to 5-day intervals during the 30-day period around the peak in cereal aphid abundance, and the number of eggs they laid in the following 24 h in the laboratory was recorded. In addition to the number of eggs laid, clutch mass, live weight, and scutum width of ovipositing females and the sizes of the clutches laid in the field were recorded. As predicted, the reproductive allocation in both species was similar. The weight of the eggs of C. septempunctata (0.20 mg) and P. quatuordecimpunctata (0.18 mg) differed little, and the proportion of body mass allocated to daily reproduction (ca. 12%) was identical in both species. In addition, the maximum number of eggs laid per day in the field by the large species was, as predicted, greater than by the small species. Interestingly, the size of the egg clutches laid by C. septempunctata in the field was similar to the daily oviposition of field-collected adults recorded in the laboratory, whereas for P. quatuordecimpunctata it was significantly smaller. The role of morphology and physiology of ladybirds in structuring aphidophagous ladybird guilds is discussed. [ABSTRACT FROM AUTHOR]

Co-extinction is the extinction of a species following the extinction of another species that it used as a resource, such as a food plant in the case of insect herbivores. The magnitude of the global co-extinction threat to two herbivorous insect taxa (aphids and scale insects) was estimated by compiling a list of species in these groups that are dependent on globally threatened trees. Eleven species of aphid (0.69%) and thirteen scale insects (1.15%) have a threatened tree as their sole host. This measure is comparable to recent estimates for insect herbivores, but far less than the published overall estimates of extinction risk for invertebrates, and highlights the dependence of insect herbivores on a wide range of habitat features. [ABSTRACT FROM AUTHOR]

The quality of different species of aphids as food for aphidiphagous ladybird beetles varies greatly. The optimal oviposition theory predicts that a female should lay eggs preferentially in patches of suitable prey and should be reluctant to oviposit in patches of less suitable prey. A no-choice experiment was used to test whether aphids (Homoptera: Aphididae) of different suitability influence the oviposition behaviour of the two-spot ladybird beetle, Adalia bipunctata (L.) (Coleoptera: Coccinellidae). The results indicate that A. bipunctata females are not more reluctant to lay eggs in the presence of moderately suitable compared to highly suitable aphids. However, females laid fewer eggs in the presence of toxic aphids. [ABSTRACT FROM AUTHOR]

Aphids and ants are two abundant and highly successful insect groups, which often live in the same habitat and therefore are likely to interact with one another. Whether the outcome of such an interaction is a predator-prey or mutualistic one is dependent on what each partner has to offer relative to the needs of the other. Consequently, understanding why some aphids enter mutualistic interactions with ants is dependent on understanding the physiological, ecological, and evolutionary traits of both partners. This includes an appreciation of the spatial, temporal, and taxonomic context in which mutualistic interactions developed. In this review, we use aphid-ant interactions to illustrate the whole range of interactions from antagonistic to mutualistic as well as to identify the processes affecting the degree of association and in particular the context within which such interactions evolved. The constraints of establishing and maintaining beneficial interactions between aphids and ants is addressed from a cost-benefit perspective. Prospects for future research are identified to further the understanding of the patterns and processes associated with aphid-ant relationships. [ABSTRACT FROM AUTHOR]

Abstract. 1. The incidence and timing of emigration, cannibalism, and intraguild predation of larvae of three aphidophagous ladybirds (Coleoptera: Coccinellidae), Harmonia axyridis Pallas, Coccinella septempunctata brucki Mulsant, and Propylea japonica Mulsant, relative to the presence of prey was determined in the laboratory in single- and mixed-species populations. 2. In single-species populations, 80% of the larvae of C. s. brucki emigrated prior to the extinction of the aphid population and no larvae were lost due to cannibalism; however > 80% of the larvae of the other two species were still present when the aphid became extinct and the losses due to cannibalism for H. axyridis and P. japonica were 25% and 14% respectively. Finally, 28% of the P. japonica larvae completed their development, whereas no larvae of the other two species became adult. 3. In mixed-species populations, mortality of P. japonica attributable to cannibalism or intraguild predation increased greatly to 60%, whereas that of the other two species remained about the same. Consequently, survival of H. axyridis larvae improved and survival of P. japonica worsened; however the survival of C. s. brucki larvae was not affected by the other two species. Early emigration by C. s. brucki larvae may have enabled them to escape intraguild predation by H. axyridis in this system. [ABSTRACT FROM AUTHOR]

Abstract. 1. The population growth of three aphid species, Metopolophium dirhodum (Walker), Rhopalosiphum padi (L.), and Sitobion avenae (F.), on winter wheat, was analysed by regression. The calculations were based on censuses of aphids made in 268 plots at 3- or 7-day intervals for 10 years on leaves and 6 years on ears. The calculations were made separately for each plot each year, then repeated on the pooled data from all plots monitored in a year. 2. At the level of individual plots, no population growth was detected at very low densities. At high densities, the populations grew exponentially and the growth rates did not decrease with increasing aphid density. 3. Significant growth was always detected in the pooled data. These growth rates decreased significantly at the highest densities. Field estimates of the intrinsic rate of increase derived from these data ranged from 0.010 to 0.026 for M. dirhodum , 0.0071–0.011 for R. padi , and 0.00078–0.0061 and 0.0015–0.13 for S. avenae , on leaves and ears respectively . 4. The apparent lack of growth in the individual plots at low densities is attributable to small sample size. It is concluded that the natural enemy ravine in the population dynamics of cereal aphids, identified by Southwood and Comins (1976), is a consequence of low population densities at which population increase is undetectable unless very large samples are taken. [ABSTRACT FROM AUTHOR]

Suggests alternative reasons for the reported relationship between tree leaf color and aphid species richness. W.D. Hamilton's theory explaining the adaptive significance of autumnal leaf colors; Basic biochemistry underlying autumn lead coloration.

Describes the theory of aerodynamics and a model of optimum partitioning of energy in aphids used to account for the relative body size of winged or unwinged aphids. Structural similarity among aphids in terms of wing area, wing beat frequency and in the relative size of thorax; Prediction that the developmental time for migrants should be longer than for nonmigrants.

1. The birch (Betula)-feeding aphid, Monaphis antennata, is always found at low densities on individual hosts and has low local abundance, but another birch-feeding aphid, Euceraphis betulae, is often found at high densities on individual hosts and has high local abundance. 2. This work attempts to establish whether the interaction between M. antennata and its host or the behaviour of individuals limits its densities. 3. Both species were reared on saplings, and population sizes were monitored for 6 weeks. Two levels of host quality were used and feeding space was kept constant throughout the experiment. Adults were prevented from leaving the saplings by clipping their wings, and predators were excluded. 4. On plants of similar host quality, both species achieved similar population sizes. 5. It is concluded that resource availability or the interactions between individuals are unlikely to be important causes of rarity. [ABSTRACT FROM AUTHOR]

To determine the causes of the variation in the seasonal dynamics of Harmonia axyridis (Pallas) in Central Europe, numbers of adults and larvae of this invasive species were recorded on trees (Acer, Betula, Tilia) throughout the growing seasons from 2011 to 2016. Each year beetles were collected every two weeks, using a standardized sweeping method. The seasonal dynamics was expressed as plots of abundance (number of individuals per 100 sweeps) against time (Julian day) and these plots (seasonal profiles) were compared in terms of their size (area under the seasonal profile curve), range, timing and height of the mode (maximum abundance). Timing and size of seasonal profiles varied among hostplants, years and sites. Abundance of larvae paralleled aphid occurrence and peak abundance of adults followed that of larvae 10 to 20 days later. Population dynamics before and after the peak were determined by dispersal. Adults arrived at sites before the start of aphid population growth and persisted there long after aphid populations collapsed. The abundance of H. axyridis decreased from 2011 to 2013 and then increased, achieving the previous levels recorded in 2015 and 2016. The variation in seasonal profiles revealed that H. axyridis, in terms of its response to environmental conditions, is a plastic species and this fl exibility is an important factor in its invasive success. [ABSTRACT FROM AUTHOR]