Abstract: Invasive species are distinguished by their rate of spread and this is thought to be associated with the ability to produce many offspring. However, it is possible that many studies do not succeed in highlighting a positive correlation between invasiveness and reproductive rate because they lack an allometric perspective. Information on the ladybird beetles introduced into North America and data on life-history traits of 30 species of ladybird beetles were used to search for a relationship between ability to invade and traits related to reproduction and dispersal. We analyzed the mechanisms responsible for the rate of spread of invasive species of the aphidophagous species of ladybird introduced into North America that became established and spread. The two largest species extended their range an order of magnitude faster than the other species. The potential reproductive rate and the speed of movement are both positively correlated with body mass, which appears to be a good predictor of the ability to spread and colonize new territory. Further studies of invasive species should therefore include an allometric perspective in order to allow comparisons between species and an assessment of the influence of reproduction and dispersal potential on the rate with which they spread when exploiting highly suitable habitats.
Abstract: The concept of intraguild predation (IGP) appeared in 1987–1989 to
describe trophic interactions within a guild of arthropods inhabiting a
sand dune desert: consumers B prey on consumers A and both of them
prey on a common resource. Theory predicts that the two types of consumers
should only coexist if consumer A is more efficient in the conversion
of the common resource than B. As a consequence, this
resource is more abundant in the presence than in the absence of intraguild
predators. Such a theoretical prediction probably explains the vivid
interest shown by ecologists involved in biological control for IGP. It is
therefore not surprising that many papers report on IGP among natural
enemies of aphids. A close examination of these reported cases indicates
that they rarely fulfil the theoretical requirements for IGP. That is, guilds
of aphidophagous insects are rarely the theatre of IGP but frequently of
interspecific predation. This is confirmed by experimental assessment of
the cost of attacking and eating intraguild prey instead of extraguild in
ladybird beetles.
Abstract: We review the chemical ecology of the ladybird beetle Harmonia axyridis from the perspective of its invasiveness and the deleterious effects it exerts in the regions it has colonised. We outline the nature and quantification of its chemical defence, and discuss the protection this provides against natural enemies, particularly intraguild predators. We consider the role of infochemicals in location of prey, intraspecific communication and intraguild interactions. We also discuss the role of prey allelochemicals in relation to H. axyridis extreme dietary generalism. Harmonia axyridis poses a number of practical problems for human health and well-being, including "ladybug taint" wine contamination and problems resulting from large aggregations overwintering in buildings. We consider chemical insights into these issues and, in particular, how attractants and repellents might help manage H. axyridis populations through a push-pull strategy. We conclude by discussing future perspectives for research.
Abstract: Environmental constraints can be determinant key factors conditioning predator
life history evolution. Prey seems to have conditioned life history evolution in their
ladybird predator, with the predators of aphids apparently presenting faster development,
greater fecundity and shorter longevity than species preying on coccids. However a rigorous
comparison has never been done. We hypothesize that aphids and coccids differ by
their developmental rate, abundance, and distribution in the field, which act as ecological
constraints promoting life history evolution in ladybird predators. Field data reveal that
aphids are ephemeral resources available in the form of large colonies randomly distributed
in the habitat whereas coccids form smaller colonies that tend to be aggregated in space
and available for longer periods. A comparison in laboratory conditions of two predatory
species belonging to the tribe Scymnini (Coleoptera: Coccinellidae) show that the aphidophagous
species lives at a faster pace than the coccidophagous: it develops faster,
matures earlier, is more fecund, has a shorter reproductive life-span and allocate proportionally
more fat in its gonads relative to soma. This indicates that the life histories of
aphidophagous and coccidophagous ladybird predators appear to have evolved in response
to particular patterns of prey availability in time and space. Under the light of these results,
the existence of a slow-fast continuum in ladybirds is briefly addressed.
Abstract: 2. This hypothesis was tested by comparing a generalist and a specialist ladybird species belonging to the same genus. 3. A resorption index was calculated for females of both species subjected to several starvation regimes. This index indicated that over a period of fasting of 3 days, the intensity of resorption was greater in the generalist than the specialist. When food was again supplied, oogenesis resumed and within 1 day was faster in the generalist than in the specialist. 4. As predicted, the resorption of oocytes and replenishment occurred faster in the generalist than in the specialist species. This is the first time, to our knowledge, that the speed and intensity of the ovarian dynamics of a predatory insect have been linked to its way of life.
Abstract: Faced with an ephemeral prey, aphidophagous ladybirds rely on the hydrocarbons present in the tracks of their larvae to choose an unoccupied patch for egg laying. Although both conspecific and heterospecific larval tracks might deter females from oviposition, the response to the later is often less striking. Several explanations have been suggested to account for this. In this paper we tested the phylogeny hypothesis, which predicts that the chemical composition of the tracks of closely related species of ladybirds will be more similar to one another than to those of more distantly related species. Qualitative and quantitative information on the chemical nature of the larval tracks and a molecular phylogeny of seven species belonging to three different genera are provided, and the congruence between these two sets of results assessed. The results confirm the phylogeny hypothesis and infer a gradual mode of evolution of these infochemicals.
Abstract: Coccinella magnifica Redtenbacher lives only in close contact with species of the Formica rufa group. Laboratory experiments were set up to determine how this species may be adapted to living with ants by comparing its behaviour with that of the closely related Coccinella septempunctata L. Eggs and larvae of C. magnifica placed on the foraging trails of ants were bitten significantly less often by the ants than those of C. septempunctata. However, the ants responded similarly to the adults of both species. For these two species, the presence of ants resulted in a significant decrease in predation efficiency. However, C. magnifica was more efficient at catching aphids in the presence of ants than C. septempunctata. The behaviour of this myrmecophilous species is discussed by taking into account that it is a generalist in terms of prey specificity.
Abstract: P> Egg cannibalism by larvae is common in Coccinellidae and is known to be advantageous for the cannibals. Furthermore, larvae of aphidophagous ladybirds usually produce an oviposition-deterring pheromone (ODP), which inhibits oviposition by adult females. It has been proposed that the response to ODP has evolved because of the high costs of cannibalism. However, this has never been formally proved. In this paper, we study the theoretical evolution of this system. We first look at the conditions under which cannibalism and the response to ODP can evolve. Subsequently, we examine the occurrence of polymorphism both in the production of larval tracks and in the sensitivity of females to specific pheromones. The models predict that the amount of cannibalism should not depend on prey density and that evolution should lead to a continuous increase in cannibalism, and consequently larvae should always cannibalize eggs when possible. In response to the cost of cannibalism, ODP recognition can evolve, so that females avoid laying eggs in patches of prey already occupied by conspecific larvae. The result is an arms race between larvae and adult females, which favours a diversification of ODP pheromones. Our models show that: (i) females should be able to recognize mixtures of hydrocarbons rather than a single molecule; and (ii) females should be more sensitive to the tracks of their own offspring than those of non-related larvae.
Abstract: Dynamics of ladybird communities (Coleoptera: Coccinellidae) and interactions with their preys on Citrus in the region of Rouiba (oriental Mitidja) Algiers. This paper aims to study the dynamics of communities of ladybirds on Citrus and their interactions with their preys and other predators. 21 species have been identified. A first trophic segregation shows the two main groups of species, some aphidophagous, other coccidiphages, totaling 17 species, representing 85.8 % of the population surveyed. Chilocorus bipunctatus, Pullus subvillosus, Nephus peyerimhoffi and, to a lesser degree, Clitostethus arcuatus and Pharoscymnus setulosus are ubiquitous on Citrus. However, Rodolia cardinalis, Mimopullus mediterraneus and Lindorus lophantae are regularly present but scarce. The years 2003 and 2004 were very favorable to beetles because of good weather and abundance of food: it was favored by fresh exuberant vegetation generated by the practice of intercropping and crop irrigation summer. The opposite has been observed since 2005, when the orchards were phased out. Most of the ladybirds breed aphid expense of the first outbreak of sap from late April to early June. However, P. subvillosus and C. bipunctatus begin to spawn a little earlier, usually around the beginning of April. The density of beetles increases with that of their prey. A variety of natural ennemies share the same food with ladybirds. They are primarily aphidophagous with 12 species belonging to six families: Coccinellidae, Syrphidae, Chrysopidae, Cecidomyiidae, Anthocoridae and Aphelinidae. The Coccinellidae and Anthocoridae are dominant with, respectively, 48.1 % and 31.3 % of the population of natural enemies of aphids, The group of coccidiphagous has 10 species in three families: The Coccinellidae, the Nutilidae and Aphelinidae. Ladybirds, mainly C. bipunctatus, are the most abundant, representing 59.2 % of natural enemies of cochineal.
Abstract: Intraspecific and interspecific predation of eggs is a well documented phenomenon amongst aphidophagous coccinellids. The invasive species Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is known to be a top intraguild predator and reported to attack the eggs of many coccinellid species both in a laboratory setting and in the wild. A previous laboratory study highlighted that while many species' eggs were highly palatable to H. axyridis, the eggs of Calvia quatuordecimguttata (Linnaeus) (Coleoptera: Coccinellidae) appeared to be extremely well protected from attack. Here we present the results of behavioural experiments testing the hypothesis that substances on the egg surface are responsible for this protection, and report preliminary results of GC-MS analysis of these compounds. When the coatings of C. quatuordecimguttata eggs were removed using hexane, they became significantly more susceptible to predation by neonate H. axyridis larvae. However, their overall palatability was not affected, in that complete consumption was never or rarely observed. This suggests that the surface compounds are a true indicator of unpalatability in this species. The effect of hexane-washing on already palatable conspecific eggs was also analysed but had no significant effect on the susceptibility of eggs to cannibalism. We conclude that the eggs of at least one European species are effectively protected by surface deterrents from intraguild predation by H. axyridis. This effect might be due to both the diversity and abundance of hydrocarbons present within the egg coating, the presence of alkenes and/or the presence of patches of a red substance on the eggs' surface, which is thought to belong to the acid group. In conjunction with data on the susceptibility of other immature stages of C. quatuordecimguttata, this finding may indicate a decreased risk of the species falling victim to invasive H. axyridis, despite their coincident habitat ranges.
Abstract: Aphids are essential for aphidophagous ladybird beetle reproduction in natural conditions. The different species of aphids vary in quality and abundance from year to year. As a consequence, females may be forced to oviposit in suboptimal colonies of prey. The relationship between the choice of oviposition sites by adults and larval performances is poorly studied in predators. To determine the performance of larvae reared oil optimal and suboptimal prey, two clutches of eggs from each of eight females of the two spot ladybird beetle, Adalia bipunctata, were used. The larvae hatching from each clutch of eggs were assigned in equal numbers to one of two groups. The larvae of one group were fed throughout their development on pea aphids (Acyrthosiphon pisum), which is a high quality prey, and the other group on cowpea aphids (Aphis craccivora), which is considered a suboptimal prey. Our results confirm that A. craccivora is a suboptimal prey for this ladybird as the adults developing from the larvae fed this aphid were lighter and had fewer ovarioles, and overall had a lower fitness than individuals reared on pea aphid. When offered a choice naive first instar larvae more frequently attacked cowpea than pea aphids. Fourth instar larvae attacked equally the two species of prey irrespective of the aphids they were previously fed. This study indicates that larvae do not show a preference for feeding on high quality aphids even though larvae that feed and complete their development on low quality prey are less fit than those that feed on high quality prey.
Abstract: Aphidophagous and coccidophagous coccinellids come into conflict with homopteran-tending ants for access to food. Antagonistic interactions between coccinellids and ants may be competitive or non-competitive. Competitive interactions occur when coccinellids attack aphids or coccids that are being tended by ants for honeydew. Non-competitive interactions include all interactions away from ant-tended homopteran colonies. We here review observations and studies of such interactions. We note that most competitive interactions occur at times when untended aphids/coccids are scarce. We describe the chemical and physical defences that coccinellids use against ant aggression and consider whether these have evolved as general anti-predator deterrents or specifically in response to ants. Myrmecophilous coccinellids are then considered, with particular focus on the two most studied species, Coccinella magnifica and Platynaspis luteorubra. We note that the myrmecophily of the two species has the same adaptive rationale-to enable the ladybirds to prey on ant-tended aphids at times of aphid scarcity-but that it is based on different traits to facilitate life with ants. Finally, we consider the role of ants in the evolution of habitat specialisation in some coccinellids.
Abstract: Aphid colonies can reach high levels of abundance but last for short periods of time. The larvae of aphidophagous ladybirds (Coleoptera: Coccinellidae) that feed on these colonies might therefore suffer from starvation, which favours the occurrence of cannibalism and intraguild predation. Thus, the assessment of patch quality becomes crucial and it has been shown that female ladybirds refrain from laying eggs in the presence of an oviposition deterring semiochemical deposited by their larvae. Adalia bipunctata (L.), Adalia decempunctata (L.) and Coccinella septempunctata L. are 3 sympatric species of ladybirds, which can co-occur in aphid colonies. As a consequence, their eggs and larvae are under threat, not only from cannibalism but also intraguild predation. Females should, therefore, also use the tracks deposited by heterospecific larvae to assess the quality of aphid colonies as oviposition sites. The expectation is that: 1- the strength of the reaction to each other's larval tracks should be correlated with percentage habitat overlap and that 2- the reaction to conspecific larval tracks should be stronger than to heterospecific tracks. In order to test these hypotheses, females' oviposition behaviour was analysed and a chemical analysis of the tracks of their larvae undertaken. The results show that oviposition behaviour is not related to habitat overlap. Both species of Adalia react to tracks of their own larvae and those of C. septempunctata, but A. decempunctata reacted more strongly than A. bipunctata. C. septempunctata reacted very slightly to its own tracks but not to those of either species of Adalia. The larval tracks are mainly composed of alkanes. Those of the two species of Adalia are qualitatively 100% similar and 60% so when the quantitative results are compared. They are, however, only 24-29% similar to those of Coccinella septempunctata.
Abstract: Life history parameters tend to differ between aphidophagous and coccidophagous ladybird beetles. It seems that the nature of prey, in particular the abundance, number and size of the colonies and their spatial distribution, may have been selected for the evolution of the life histories in these two groups of coccinellids, leading the aphidophagous ladybird beetles to develop at a fast pace and the coccidophagous beetles at a slower pace. To study the abundance, number and size of the colonies and the spatial distribution of aphid and coccid species, 100 sampling plots regularly spaced along four parallel transects were surveyed in the summer of 2004. At each sampling plot, species abundance, and the number and size of colonies of aphid and coccid species were recorded. Iwao's patchiness regression was used to assess the spatial distribution of aphids and coccids. From this study, it was found that coccids are much rarer than aphids but formed more colonies. Whereas aphids display a stonger tendency to crowding, aphid colonies are randomly distributed in space while coccid groups are aggregated. So, it seems that the abundance and spatial distribution of prey may be factors selecting for the evolution of different life histories among aphidophagous and coccidophagous ladybird beetles.
Abstract: As is the case for other insects ovipositing on or in resources that are limited in time and/or space, the two-spot ladybird beetle, Adalia bipunctata (L.) produces an oviposition-deterring pheromone (ODP), which is produced by the larval stages. Foraging larvae touch the substrate with their tarsi and the anal disk on the tenth abdominal segment. The aim of this paper was to determine whether the ODP produced by larvae was deposited by the tarsi or the anal disk. Fourth instar larvae either had their anal disk and tarsi, or anal disk, or tarsi coated with a water-soluble mounting medium. Larvae so treated were allowed to walk on filter paper that was subsequently presented to gravid females. The tracks of larvae that had both their tarsi and anal disk masked did not inhibit oviposition. However, the tracks of larvae that had only their tarsi masked significantly inhibited oviposition but those of larvae that had only their anal disk masked did not. It is concluded that the ODP is deposited on the substrate by the anal disk on the tenth abdominal segment of larvae.
Abstract: Life history parameters tend to differ between aphidophagous and coccidophagous ladybird beetles. It seems that the nature of prey, in particular the abundance, number and size of the colonies and their spatial distribution, may have been selected for the evolution of the life histories in these two groups of coccinellids, leading the aphidophagous ladybird-beetles to develop at a fast pace and the coccidophagous beetles at a slower pace. To study the abundance, number and size of the colonies and the spatial distribution of aphid and coccid species, 100 sampling plots regularly spaced along four parallel transects were surveyed in the summer of 2004. At each sampling plot, species abundance, and the number and size of colonies of aphid and coccid species were recorded. Iwao's patchiness regression was used to assess the spatial distribution of aphids and coccids. From this study, it was found that coccids are much rarer than aphids but formed more colonies. Whereas aphids display a stonger tendency to crowding, aphid colonies are randomly distributed in space while coccid groups are aggregated. So, it seems that the abundance and spatial distribution of prey distribution may be factors selecting for the evolution of different life histories among aphidophagous and coccidophagous ladybird beetles.
Abstract: 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: Episyrphus balteatus (DeGeer) (Diptera: Syrphidae), Adalia bipunctata (L.) (Coleoptera: Coccinellidae) and Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae) are the three most abundant natural enemies of Dysaphis plantaginea Passerini (Homoptera: Aphididae) in Asturian (NW Spain) apple orchards. They attack this aphid in sequence: E. balteatus arrived first, followed by A. bipunctata and then by A. aphidimyza. The cecidomyiids arrived too late to have a regulating effect. The syrphids laid an average of 2.3 +/- 1.7 eggs per aphid colony and the coccinellids 18.4 +/- 9.9 regardless of the degree of the infestation rates of the apple shoots. This value corresponds to the size of an egg batch laid by one female. Therefore, these aphid predators did not respond numerically to the abundance of the pest. The results of this study indicate that natural populations of syrphids and ladybird beetles are unable to control D. plantaginea, and therefore a more complex strategy than waiting for natural enemies is required.
Abstract: 1. Dynamic models of optimal foraging predict that an animal's decision to accept or reject a patch depends not only on the environment and patch quality, but also on its internal state. Previous experiments have shown that the two-spot ladybird beetle, Adalia bipunctata (L.), is reluctant to lay eggs in a patch of prey contaminated by the oviposition-deterring pheromone produced by conspecific larvae. 2. An experiment was conducted to test whether the internal state of an A. bipunctata female affects its oviposition response to oviposition-deterring pheromone. Firstly, the oviposition response to oviposition-deterring pheromone of young and old females was compared. Secondly, the oviposition response to oviposition-deterring pheromone of females previously exposed continuously to oviposition-deterring pheromone was compared with that of females of the same age but with no previous experience of oviposition-deterring pheromone. 3. Old females and females with previous experience of oviposition-deterring pheromone were less reluctant to lay eggs in the presence of oviposition-deterring pheromone than young and naive females. These results are consistent with the predictions of optimal foraging theory.
Abstract: Dysaphis plantaginea is one of the major pests of apple trees in Western Europe. It is usually recommended that apple trees be sprayed with insecticide as soon as the first aphid is recorded. Thus, orchards are sprayed with insecticide almost every year although aphids rarely remain abundant for several successive growing seasons. Consequently signs of resistance to pesticides in the aphid have already been recorded. Therefore, fruit growers are willing to become less dependent on insecticides and to adopt an integrated pest management approach. One of our aims is to understand the population dynamics of D. plantaginea in order to develop a forecasting model. The factors associated with seasonal increases in aphid abundance are known for several pest species and have been used to develop such models. As the catches of aphids by suction traps are well correlated with aphid abundance on adjacent crops, data from the Agraphid network have been used to search for patterns in the population dynamics of D. plantaginea. Analysis of the yearly variations in D. plantaginea numbers indicates density dependence.
Abstract: Mills (1982) formulated the satiation hypothesis in order to explain why ladybirds are generally more effective in the biological control of coccids than of aphids: aphidophagous ladybirds are supposedly less efficient because they become more rapidly satiated than coccidophagous ladybirds. If this is true, the former should spend less time eating than the latter. This hypothesis is tested in this study using the coccidophagous Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) and the aphidophagous Adalia bipunctata (L.) (Coleoptera: Coccinellidae). Contrary to Mills' (1982) prediction the coccidophagous ladybird did not feed continuously and even spent less time feeding than the aphidophagous ladybird. Furthermore, the gut capacity of C. montrouzieri is smaller than that of A. bipunctata.
Abstract: The size distribution of the species of a wide range of plants, herbivores, and carnivores are similar in form, i.e.. right skewed when size is plotted logarithmically. In addition to differential extinction and speciation rates, it is argued that allometric constraints determine the efficiency with which resources are converted into offspring, which in turn determines the frequency of species of different body sizes. In looking for a general explanation for the size distribution shown by all organisms, theorists currently tend to favor explanations based on physiological rather than ecological constraints. Of the body size distributions of predatory ladybird beetles in the Palearctic. Nearctic, Ethiopian, and Australian regions, only that for the Nearctic is significantly right skewed. Even within the Palearctic, the form of the distribution differs among countries, with that for Japan significantly right skewed and that for Central Europe significantly left skewed. An analysis of the prey of ladybirds indicates that increasing ladybird size is associated with increase in size and/or mobility of their prey. The smallest species feed on mites, and the largest on caterpillars and beetle larvae. In addition, the ratio of the numbers of species of aphidophagous to coccidophagous ladybirds in the Nearctic and Palearctic regions reflects the ratio of the numbers of species of aphids to coccids in these two regions. The relationships between egg and adult volumes for 61 species, and egg and adult masses for 26 species both indicate that large species lay larger eggs than small species. In particular, the predators of large and/or active prey lay larger eggs than the predators of small and/or slow moving prey. The relevance of these findings to our understanding of the factors that have shaped body size frequency distributions is discussed. In the case of predatory ladybirds it is concluded that the shape of their body size distribution curves is determined by the nature and the relative abundance of their prey, that is., by ecological rather than physiological constraints.
Abstract: After emergence from pupae males and females of Adalia bipunctata reared under the same constant conditions showed similar refractory periods in their mating behavior. The statistically significant slight protogyny might indicate that it is advantageous for females to accept mating and stove sperm for a short period prior to becoming sexually mature, whereas males need to become sexually mature in order to mate. As the two-spot ladybird has overlapping generations, theory predicts that the most effective strategy for both sexes is to have similar sexual maturation periods. The results of this study support this prediction, The actual lengths of the maturation periods, however, will depend largely on the prevailing temperatures and the quality and quantity of food available to the beetle.
Abstract: Aphidophagous ladybirds are reluctant to oviposit in patches of prey where conspecific larvae are present. This is adaptive as larval cannibalism is a major threat to egg survival. Ladybirds avoid laying eggs in such patches by responding to a species specific oviposition deterring pheromone present in the tracks of larvae. This study revealed that the oviposition deterring pheromone consists of a mixture of alkanes of which n-pentacosane is the major component (15.1%). These alkanes are likely to spread easily on the hydrophobic cuticle of plants and so leave a large signal. In addition, they are not quickly oxidized and therefore provide a long lasting signal. The latter was confirmed by the observation that 10 day old tracks still deterred oviposition.
Abstract: Coccinella septempunctata was approximately 20% more reluctant to eat the eggs of Adalia bipunctata than the reverse. In addition, fourth instar larvae of C. septempunctata failed to complete their development on a diet of A. bipunctata eggs and only 30% of those of A. bipunctata completed their development on a diet of C. septempunctata eggs, and the survivors took nearly 2 times as long as those fed aphids. This is an indication that the costs of intraguild predation might outweigh the benefits.
Abstract: Adults of the Syrphinae subfamily display no strong flower preferences but exploit pollen and nectar produced by native plants having large inflorescences and flat corollae (e.g. Apiaceae, Asteraceae, Ranunculaceae and Rosaceae). Seven foraging guilds are defined according to the dietary patterns of hoverflies, reflecting mainly a sequential exploitation of flowers at different times of the year and in different habitats. The majority of species live in forests where they form highly diversified communities. Few Syrphinae colonize successfully open and anthropogenic habitats, such as field margins and fallow areas. Episyrphus balteatus. Melanostoma mellinum, Eupeodes corollae. Sphaerophoria scripta and Plutycheirus spp. are dominant in the communities of Syrphinae from open habitats, all over western Europe. These species are highly polyphagous and characterized by elongated mouthparts as well as a long and slender body. They have access to pollen and nectar in flowers with small and tubular corollae. It is suggested that their polyphagy is an important asset for colonizing open and ephemeral habitats.
Abstract: Certain alkanes or their mixture present on the surface of ladybird elytra is important in the recognition of potential mates. Similar chemicals are present in the tracks of larvae, which deter conspecific female ladybirds from laying eggs in aphid colonies already being attacked by larvae. Finally, the shell of ladybird eggs is covered with alkanes that deter other species of ladybirds from eating the eggs. In each case the alkanes are similar although they fulfil different functions. There are, therefore, indications that ladybirds exploit their natural product with parsimonious versatility.
Abstract: The eggs of some ladybirds are known to be toxic to intraguild ladybird predators. However, this defence is of little value if the eggs are killed before their toxicity becomes apparent. The results presented in this paper indicate that chemicals on the surface of the eggs of two species of ladybirds signal the relative risk of cannibalism and intraguild predation. In Adalia bipunctata and Coccinella septempunctata, 87% of the chemicals are alkanes. Each species of ladybird is less reluctant to eat their own eggs than those of the other species. This asymmetry is to be expected because there is a greater risk to ladybirds from intraguild predation than cannibalism. Similar alkanes to those on the sur face of the eggs of A. bipunctata are present in tracks left by larvae and on the elytra of the adults of this species. Those in the larval tracks deter females from ovipositing in patches of prey already being attacked by their larvae and those on the elytra are used in mate recognition. That different context dependent messages could be signalled by similar chemicals is an example of semiochemical parsimony.
Abstract: Young larvae of Adalia bipunctata search an area more intensively when exposed to the odour from other larvae feeding on aphids than when exposed only to the odour of aphids. In an olfactometer young larvae were significantly attracted either to the odour of crushed aphids or larvae feeding on aphids, but not to that of aphids, larvae, larvae plus aphids or larvae feeding on an artificial diet. That is, the change in searching behaviour appears in response to a volatile released by aphids when attacked. The odour released by crushed aphids is made up entirely of aphid alarm pheromone, beta -farnesene. It is likely that the adaptive significance of this response is that it increases the ability of larvae to locate larvae that have already caught prey. By sharing the aphid kill of another larva it is likely that a first instar ladybird larva greatly increases its probability of surviving to the next instar. It is suggested that this social feeding is facilitated by egg clustering, which also may additionally account for why aphidophagous ladybirds lay their eggs in clusters.
Abstract: Foraging theory indicates that aphid predators should lay their eggs early in the development of an aphid colony. Hoverflies appear to respond to cues associated with the age of an aphid colony in assessing its quality for oviposition. However, in the study reported here, ovipositing two-spot ladybirds did not respond differentially to two cues, in various combinations, associated with the age of aphid colonies on herbaceous plants: (a) age structure of the aphid colony and (b) the age of the plant. Thus, this aphid predator appears to be mainly using cues associated with the presence of conspecific larvae rather than those associated with aphids and/or plants when assessing patch quality.
Abstract: Episyrphus balteatus only matures eggs after emergence. Ovaries develop in 4 stages. In the absence of oviposition sites, females refrain from ovipositing and their ovaries progressively fill the abdomen and then egg resorption occurs. The potential fecundity, which is expressed by the ovariole number, the reproductive biomass and the abdomen volume, scales isometrically with the size of females. Egg size is much less variable and does not rise proportionally to body size. In laboratory conditions, females of E. balteatus might lay between 2,000 and 4,500 eggs during their life-time at a rate of 1 to 2 eggs per ovariole per day. Both lifetime fecundity and rate of egg production are directly related to the size of females. The potential and realized fecundities are likely to be limited by the availability of food resources during larval and adult life, respectively.
Abstract: The impact of augmentative releases of larvae and eggs of the indigenous ladybird beetle Adalia bipunctata (L.) (Coleoptera: Coccinellidae) against the rosy apple aphid Dysaphis plantaginea Pass. (Homoptera: Aphididae), a major pest insect on apple trees, was assessed in field experiments in Switzerland, during 1997. In a first experiment, eggs and larvae were released on 3-year old apple trees infested with five aphids at four different predator-prey ratios (0:5, 1:5, 1:1, 5:1). In a second experiment, eggs and larvae were released at a predator-prey ratio of 5:1 on branches of apple trees naturally infested with aphids. In both experiments, the interaction with ants was taken into account and the releases were done at two different times in spring. The results showed that an augmentative release of larvae significantly prevented the build-up of colonies of D. plantaginea. Significant reductions in aphid numbers were recorded at the two highest predator-prey ratios, 1:1 and 5:1. Larvae were efficient just before flowering of apple trees at a time when growers normally have to spray their trees. On trees where ants were present the larvae of A. bipunctata were significantly less efficient. Effects of eggs of A. bipunctata, however, were less reliable. At the first date of release (5 April), they did not hatch, probably as a consequence of bad weather conditions.
Abstract: On encountering a mature female, a male of the two-spot ladybird, Adalia bipunctata (L.), first palpated her elytra with his maxillary palps, then mounted her, extruded his penis and mated. Copulation never occurred between active males but males copulated with dummies bearing male elytra as frequently as with dummies with female elytra of their own species. Similarly, males attempted mating with immobilised conspecifics of both sexes. However elytra washed in chloroform failed to stimulate mating. Analysis of the chloroform extracts of the elytra revealed that male and female ladybirds are coated by the same blend of hydrocarbons among which 9- and 7-methyl tricosane are dominant. Our results are consistent with a role of these cuticulars hydrocarbons in species recognition and show that behaviour, in particular movement, is necessary for discrimination between males and females. (C) 1998 Elsevier Science Ltd. All rights reserved.
Abstract: Gravid females of the two-spot ladybird, Adalia bipunctata (L.), were deterred from ovipositing when kept in petri dishes that had previously contained conspecific larvae but not conspecific adults, or the larvae of another two species of ladybird, Adalia decempunctata (L.) and Coccinella septempunctata L. The deterrent effect was density dependent and mediated via a chloroform-soluble contact pheromone present in the larval tracks. Similarly, gravid females of C. septempunctata were deterred from ovipositing by conspecific larval tracks and chloroform extracts of these tracks, but not by the tracks or extracts of tracks of A. bipunctata larvae. That is, in ladybirds the larvae produce a species-specific oviposition-deterring pheromone. In the field, the incidence of egg cannibalism in ladybirds increases very rapidly with the density of conspecific eggs or larvae per unit area. Thus, in responding to the species specific oviposition deterring pheromone female ladybirds reduce the risk of their eggs being eaten and spread their offspring more equally between patches.
Abstract: Cannibalism occurred frequently in a laboratory population of Episyrphus balteatus. The third instar larva was the most voracious cannibal and ate mainly eggs. Pupae were never eaten. Egg cannibalism was inversely dependent on aphid density, but even occurred when prey was present in excess. Syrphid larvae can complete their development on conspecific eggs.
Abstract: Aphidophagous ladybirds tend to lay eggs close to their prey and their voracious larvae forage in a way that results in them remaining in or close to aphid colonies. Although ladybird beetles have frequently been used to control aphids, they are rarely effective in reducing aphid abundance. Aphids have very high rates of increase and are very sensitive to changes in the quality of their host plants. On average, aphid colonies rarely last for more than a month. That is, they are a very unstable food resource for predators. In addition, the developmental time of ladybirds is about a month. As a consequence ladybirds face two risks. If they lay their eggs too late in the development of an aphid colony, the larvae will not mature before prey becomes scarce. If they lay too many eggs their larvae will severely restrict the rate of increase of the aphids and cause an earlier collapse of the colony. In order to survive the larvae will then have to resort to cannibalism. Theory indicates that the best strategy for optimizing fitness is for ladybirds to lay a few eggs at the beginning of the development of aphids colonies. Both experimental and field data indicate that is what ladybirds do, i.e., they behave as if they are 'prudent predators'. This accounts for why aphidophagous ladybirds have been very ineffective biological control agents.
Abstract: Aphidophagous species of ladybirds have generally proved ineffective biocontrol agents, whereas many coccidophagous species have proved very effective, especially Rodolia cardinalis (Caltagirone & Doutt, 1989). Two hypotheses have been proposed to account for this pattern: the optimum food utilization/satiation hypothesis (Mills, 1982) and the generation time ratio hypothesis (Kindlmann & Dixon, 1996). In this paper the extensive literature on ladybirds is used to test these hypotheses.
Abstract: Adalinine (2), a new piperidine alkaloid, has been isolated from the European two-spotted ladybird beetle Adalia bipunctata, and its structure has been determined by spectroscopic methods. This alkaloid was also shown to be present in all the life cycle stages of Adalia bipunctata as well as in the adults of a related species, A. decempunctata.
Abstract: 1. Adult males of the two-spot ladybird beetle, Adalia bipunctata, did not show a functional response to increase in aphid abundance and consumed markedly fewer aphids than do the females. 2. At high densities of prey, females spent more time in area-restricted search than when prey was scarce. Males were always less active than females and they did not respond to an increase in prey abundance by a change in searching behaviour. 3. After a brief encounter with a female, a male showed area-restricted searching behaviour. This behaviour occurred in response to encountering a female's elytra and in particular to a chloroform-soluble component (sex pheromone) present on or in the elytra. 4. Males needed to encounter a female in order to respond to her presence, which indicated the pheromone is a contact pheromone. 5. The searching behaviour of males appeared to be mainly directed towards locating females; that of females towards locating aphids. This difference between the sexes should be taken into account when quantifying the predatory response of ladybirds to aphid abundance in the field.
Abstract: Coccinellids and syrphids that feed on aphids and coccids face the same problem: an unstable food supply. Their eggs and larvae face cannibalism and/or starvation if the aphid colony they attack declines in abundance before they mature. Optimal foraging theory predicts that such predators should lay a few eggs early in the development of an aphid colony. Studies on two species of coccinellid and one species of syrphid revealed that they do respond to the quality as well as the abundance of their prey. By refraining from laying eggs in aphid colonies already exploited by predators and those that are shortly to decline in abundance when the aphids disperse, these predators are able to forage in a way that is consistent with the predictions of optimal foraging theory.
Abstract: An esterase polymorphism in Tribolium castaneum has been detected and studied during ontogenesis. The presence of a biochemical marker throughout development offers many possibilities to follow the development of pest infestations in storage systems and to analyze flow of genes conferring resistance to insecticides into this closed ecosystem.
Abstract: Temporal changes in aphid abundance pose a considerable challenge to ovipositing aphidophagous ladybirds, as in order to maximize their fitness they need to synchronize their reproduction with the early development of aphid populations. Field census data and laboratory experiments were used to determine how ovipositing females of the two-spot ladybird, Adalia bipunctata (L.), assess whether an aphid population is suitable for exploitation. In the field, two-spot ladybirds usually laid eggs well before aphid populations peaked in abundance. In the laboratory they showed a marked reduction in their reproductive numerical response in the presence of larvae of their own species but not of other aphidophagous ladybirds. At the highest aphid density this was not a consequence of competition for food between larvae and ovipositing females. In the presence of conspecific larvae gravid females were very active and as a consequence more likely to leave an area, and when confined with other conspecific females or larvae laid fewer eggs and later than females kept on their own. The extent of the inhibition of egg laying is negatively correlated with the rate of encounter with larvae. Thus it is proposed that gravid females appear mainly to use the presence of conspecific larvae to assess the potential of an aphid colony for supporting the development of their offspring.
Abstract: Ladybird species of different sizes make a proportionally similar investment in reproduction in terms of biomas of gonads and reproductive rate. In particular egg size multiplied by egg number is proportional to adult weight. Thus egg size is a function of adult weight and ovariole number. Species with few ovarioles lay larger eggs than similar-sized species with many ovarioles. Development time is a function of the ratio of adult to egg weight such that species with proportionally small eggs take longer to complete their development than do species with proportionally large eggs. Egg size is probably constrained by the minimum size at which first instar larvae can capture active prey and complete their development before prey becomes scarce.
Abstract: In females of Adalia bipunctata (LINNAEUS, 1758), there are exocrine glands associated with the coxites that form part of the genitalia. The coxites are extended anteriorly in the form of a gutter with the concavity orientated towards the vagina. The edges are continuous with a shiny membrane that forms a coxal reservoir. The concave side of this gutter-like extension is lined by a layer of glandular cells. Their ultrastructure is typical of the type 1 insect epidermal cells of NOIROT and QUENNEDEY (1974). The coxal cells undergo a three stage activity cycle that is synchronised with the ovarial activity and correlated with ladybrid age. The huge development of the smooth endoplasmic reticulum in the third stage of the activity cycle indicates that terpenoid substances are produced. On the basis of behavioural observations we suggest that these exocrine glands have a role in the sexual behaviour of A. bipunctata although we cannot exclude a role in the chemical protection of eggs.
