Factors affecting orchard colonisation by the black-kneed capsid (Blepharidopterus angulatus (Hemiptera:Miridae)) from alder windbreaks

The colonisation of orchards by Blepharidopterus angulatus (the black-kneed capsid bug) from alder windbreaks was investigated, to determine its use as a biological control agent of orchard pests. The aphid Pterocallis alni provides an abundant and acceptable food for the capsid on alder. The key capsid mortality factor on windbreaks was the loss of adult females through migration. Clipping the windbreak prior to the aphid population peak resulted in male capsids migrating and females remaining, while clipping after the aphid population peak resulted in both sexes migrating to nearby orchards. Guidelines are given for windbreak management as part of a system of integrated orchard pest control.     

Ecology of the parasites of a predatory bug, Blepharidopterus angulatus (Fall.)

Abstract. 1. On lime, Blepharidopterus angulatus is parasitized by a braconid, Peristenus sp., which is attacked by an ichneumonid hyperparasite, Mesochorus sp. The emergence and oviposition behaviour of the adult parasites and the growth of the larvae are described.
2. Parasitized B. angulatus are considerably heavier at maturity than normal, and nymphs parasitized by Peristenus consume, during their fifth instar, 2.1 times more in dry weight of prey (lime aphids). The growth efficiency of Peristenus is 30–37%.
3. An inverse relationship between percentage parasitism and host density on different trees may have been due to differences in synchronization.     

Population regulation in the lime aphid

The results from a long-term field study (10 years) and laboratory experiments have been used to develop a simulation model of lime aphid populations. This has revealed that the numbers of this aphid are regulated by an interaction between predation and aphid flight. These normally pre-empt regulation by aphid induced changes in plant quality causing increased flight and mortality later in the year.     

The influence of population density on the flight behaviour of the lime aphid, Eucallipterus tiliae

The effects of high population density on the flight behaviour of laboratory — reared lime aphid virginoparae are described. The aphids show a heightened flight response to direct crowding and to the effects on the leaves of their host plant of previous high numbers of aphids. Sensitivity to direct crowding occurs at both the nymphal and adult stages, the effects being additive in determining the likelihood of an aphid flying. The nymphs receive information on the state of crowding through the leaf, possibly in the form of salivary substances injected by other aphids and imbibed by the nymphs. The adults respond to the increased tactile stimulation from other aphids brought about by crowding. The significance of this behaviour in the population dynamics of the aphid is discussed.

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Résumé Les effets d'une forte densité de population sur le comportement de vol de virginipares du Puceron du tilleul élevé en laboratoire sont décrits. Les Pucerons montrent une forte réponse de vol en rapport direct avec la surpopulation et en rapport également avec les effets sur les feuilles de la plante-hôte de précédents rassemblements d'un grand nombre d'aphides. La sensibilité directe à la surpopulation se manifeste à la fois chez les stades pré-imaginaux et imaginaux, les effets s'additionnant pour déterminer la probabilité d'un vol d'aphides. Les stades pré-imaginaux sont imformés de l'état de surpeuplement, par l'intermédiaire de la feuille, peut être par des substances salivaires injectées par d'autres aphides et réabsorbées. Les adultes répondent à la stimulation tactile venant des autres individus, stimulation qui s'accroît avec la surpopulation. La signification de ce comportement dans la dynamique des populations de l'aphide du tilleul est ici discutée.

     

Aggregation in the lime aphid (Eucallipterus tiliae L.)

Summary Lime aphids feed on the contents of sieve tubes in the leaf veins. Aphids on the undersides of large leaves tend to select the smallest veins, while those on small leaves tend to select the larger veins. This tendency increases with the size of the aphid. Since only 4% of the total leaf area is covered by the larger veins, crowding is imposed on those aphids feeding from them. In spring, when the leaves are young and small, close spacing of the aphids results due to their tendency to select large veins. In summer, when the leaves are mature and large, wider spacing between aphids occurs due to their tendency to occupy more of the leaf surface.     

Heterogeneous landscapes and the role of refuge on the population dynamics of a specialist predator and its prey

How, and where, a prey species survives predation by a specialist predator during low phases of population fluctuations or a cycle, and how the increase phase of prey population is initiated, are much-debated questions in population and theoretical ecology. The persistence of the prey species could be due mainly to habitats that act as refuges from predation and/or due to anti-predatory behaviour of individuals. We present models for the former conjecture in two (and three) habitat systems with a specialist predator and its favoured prey. The model is based on dispersal of prey between habitats with high reproductive output but high risk of predation, and less productive habitats with relatively low risk of predation. We illustrate the predictions of our model using parameters from one of the most intriguing vertebrate predator–prey systems, the multi-annual population cycles of boreal voles and their predators. We suggest that cyclic population dynamics could result from a sequence of extinction and re–colonization events. Field voles (Microtus agrestis), a key vole species in the system, can be hunted to extinction in their preferred meadow habitat, but persist in sub-optimal wet habitats where their main predator, the least weasel (Mustela nivalis nivalis) has a low hunting efficiency. Re–colonization of favourable habitats would occur after the predator population crashes. At the local scale, the model suggests that the periodicity and amplitude of population cycles can be strongly influenced by the relative availability of risky and safe habitats for the prey. Furthermore, factors like intra-guild predation may lead to reduced predation pressure on field voles in sub-optimal habitats, which would act as a refuge for voles during the low phase of their population cycles. Elasticity analysis suggested that our model is quite robust to changes in most parameters but sensitive to changes in the population dynamics of field voles in the optimal grassland habitat, and to the maximum predation rate of weasels.     

Effects of point mutations in the major capsid protein of beet western yellows virus on capsid formation,virus accumulation,and aphid transmission

Point mutations were introduced into the major capsid protein (P3) of cloned infectious cDNA of the polerovirus beet western yellows virus (BWYV) by manipulation of cloned infectious cDNA. Seven mutations targeted sites on the S domain predicted to lie on the capsid surface. An eighth mutation eliminated two arginine residues in the R domain, which is thought to extend into the capsid interior. The effects of the mutations on virus capsid formation, virus accumulation in protoplasts and plants, and aphid transmission were tested. All of the mutants replicated in protoplasts. The S-domain mutant W166R failed to protect viral RNA from RNase attack, suggesting that this particular mutation interfered with stable capsid formation. The R-domain mutant R7A/R8A protected approximately 90% of the viral RNA strand from RNase, suggesting that lower positive-charge density in the mutant capsid interior interfered with stable packaging of the complete strand into virions. Neither of these mutants systemically infected plants. The six remaining mutants properly packaged viral RNA and could invade Nicotiana clevelandii systemically following agroinfection. Mutant Q121E/N122D was poorly transmitted by aphids, implicating one or both targeted residues in virus-vector interactions. Successful transmission of mutant D172N was accompanied either by reversion to the wild type or by appearance of a second-site mutation, N137D. This finding indicates that D172 is also important for transmission but that the D172N transmission defect can be compensated for by a "reverse" substitution at another site. The results have been used to evaluate possible structural models for the BWYV capsid.     

Influence of six aphid prey species on development and reproduction of a ladybird beetle, Coccinella septempunctata

Pre-imaginal development, immaturesurvival, and reproduction of a ladybird, Coccinella septempunctata Linnaeus, werestudied in response to six aphid species, Aphiscraccivora Koch, Aphis gossypii Glover,Aphis nerii Boyer de Fonscolombe,Lipaphis erysimi (Kaltenbach), Myzuspersicae (Sulzer) and Uroleuconcompositae (Theobald) to quantify theirrelative suitability as prey. Pre-adultdevelopment was shortest (13.93 ± 0.12 days)when fed on L. erysimi and longest(22.85 ± 0.10 days) on A. nerii. Immaturesurvival, adult emergence, growth index,relative growth rate, development rate, maleand female longevity, oviposition period,fecundity and hatching percent were maximal, i.e. 73.47 ± 0.89%, 90.07 ± 1.43%,8.62 ± 0.23, 1.52 ± 0.02, 0.07,81.10 ± 1.26 days, 85.70 ± 1.45 days,69.80 ± 1.32 days, 1764.10 ± 8.46,and 87.88 ± 1.05, respectively when C.septempunctata were fed on L. erysimi.The same parameters were minimal, i.e.43.86 ± 1.33%, 71.65 ± 2.75%,2.02 ± 0.08, 0.49 ± 0.02, 0.04,44.40 ± 1.39 days, 53.50 ± 1.00 days,16.40 ± 0.60 days, 203.20 ± 11.83, and48.68 ± 2.06, respectively on A. nerii. Theweights of different ladybird life stages weremaximal after feeding on L. erysimi and minimalon A. nerii. Regression analyses of thedata revealed linear relationships betweendevelopment rate and weight of adult; dailyprey consumption and relative growth rate; logweight of adult male and female; and longevityand fecundity of female. On the basis of thesefindings, the order of suitability of aphidspecies for C. septempunctata is L. erysimi >M. persicae > A. craccivora > A. gossypii >U. compositae > A. nerii. Thus, the presentinformation can be utilized for the massrearing of C. septempunctata by supplyingthe best food and can also help in theprediction of the relative abundance of theladybird on different aphid infestations in thefields.     

Factors influencing aggregation between nymphs of the lime aphid, Eucallipterus tiliae (L.)

Abstract. 1. Aggregation in the lime aphid is influenced by the newly-born nymphs staying close to their mother.
2. The aggregations are brought about by gregariousness between the first instar nymphs and their reluctance to move far from their birthplace.
3. As the nymphs mature they become more wide-ranging and leave the aggregation. Dispersal is also promoted by a lack of gregariousness between different instars.
4. Such aggregations remain intact only as long as the adult continues to reproduce the relatively sedentary first instars.
5. The significance of this behaviour in the spacing of the lime aphid is discussed.     

The effect of aphid prey quality on searching behaviour of Adalia bipunctata and its susceptibility to insecticides

After consumption of one individual of a suitable prey, such as Phorodon humuli (Schrank) (Aphididae), Adalia bipunctata L. (Coleoptera, Coccinellidae) adults changed from extensive to intensive searching behaviour. However, after the consumption of one individual of three other aphid species: Aphis fabae Scop., Aphis craccivora Koch or Aphis spiraephaga Müller, which are unsuitable prey, this coccinellid remained immobile for 12–76 min and did not switch to intensive search after moving off. Adult A. bipunctata fed an unsuitable prey, A. fabae, for 2 weeks were 2–4 times more susceptible to pyrethroid insecticides (permethrin, deltamethrin, fenpropathrin, esfenvalerate, alfa-cypermethrin and bioresmethrin) and insect growth regulators (diflubenzuron, triflumuron, fenoxycarb, flufenoxuron, teflubenzuron) than those fed a suitable prey, P. humuli.The searching behaviour of coccinellids could thus be another criterion for determining the suitability of aphids as prey. The fact that the nutritional quality of aphids can affect the susceptibility of predatory coccinellids to insecticides should be borne in mind in integrated pest management programs.     

Metabolic acclimatization to seasonal changes in temperature in the sycamore aphid,Drepanosiphum platanoides (Schr.), and lime aphid,Eucallipterus tiliae L.

Summary Both sycamore and lime aphids live on the leaves of their respective host trees. The sycamore aphid unlike the lime aphid has the ability to adapt metabolically to changes in temperature. The difference in ability of these two tree-dwelling aphids to adapt metabolically to changes in temperature can be related to their mode of life. The sycamore aphid lives on sycamore which is native to the mountainous areas of southern and central Europe where conditions are cool. Sycamore also has a longer growth period than lime as its buds burst earlier and it sheds its leaves later. Sycamore aphids are therefore naturally exposed to a wider range of temperatures than lime aphids.     

The control of seasonal changes in the pigmentation of lime aphid nymphs, Eucallipterus tiliae

Lime aphid nymphs may be found with or without bands of black pigment on the dorsal surfaces of the head, thorax and abdomen. The proportion of pigmented nymphs in a population varies during a season, although first generation nymphs are always unpigmented. The appearance of the black pigment is found to be induced by both crowding and changes in the leaves associated with leaf maturity. Since the crowding stimulus is also found to be transmitted via the leaf, this suggests that pigmentation may be ultimately controlled by a single plant-borne factor, possibly the nutritional quality of the leaves. The possible significance of this response in the life of the aphid is discussed.

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zusammenfassung Bei der Lindenblattlaus können Larven mit und ohne schwarz pigmentierten Bändern auf der Rückenseite des Kopfs, des Thorax und des Abdomens gefunden werden. Der Anteil pigmentierter Larven in einer Population schwankt während einer Saison, indessen sind die Larven der ersten Generation nie pigmentiert. Das schwarze Pigment wird induziert durch Crowding und durch Veränderungen im Blatt, welche mit der Blattreifung zusammenhängen. Da auch der Crowdingstimulus durch das Blatt übertragen wird, dürfte die Pigmentierung letztlich durch einen einzigen in der Pflanze befindlichen Faktor, möglicherweise die Nahrungsqualität der Blätter, gesteuert werden. Die mögliche Bedeutung dieses Zusammenhangs im Leben der Blattlaus wird diskutiert.

     

Predator functional response and prey survival: direct and indirect interactions affecting a marked prey population

1. Predation plays an integral role in many community interactions, with the number of predators and the rate at which they consume prey (i.e. their functional response) determining interaction strengths. Owing to the difficulty of directly observing predation events, attempts to determine the functional response of predators in natural systems are limited. Determining the forms that predator functional responses take in complex systems is important in advancing understanding of community interactions. 2. Prey survival has a direct relationship to the functional response of their predators. We employed this relationship to estimate the functional response for bald eagle Haliaeetus leucocepalus predation of Canada goose Branta canadensis nests. We compared models that incorporated eagle abundance, nest abundance and alternative prey presence to determine the form of the functional response that best predicted intra-annual variation in survival of goose nests. 3. Eagle abundance, nest abundance and the availability of alternative prey were all related to predation rates of goose nests by eagles. There was a sigmoidal relationship between predation rate and prey abundance and prey switching occurred when alternative prey was present. In addition, predation by individual eagles increased as eagle abundance increased. 4. A complex set of interactions among the three species examined in this study determined survival rates of goose nests. Results show that eagle predation had both prey- and predator-dependent components with no support for ratio dependence. In addition, indirect interactions resulting from the availability of alternative prey had an important role in mediating the rate at which eagles depredated nests. As a result, much of the within-season variation in nest survival was due to changing availability of alternative prey consumed by eagles. 5. Empirical relationships drawn from ecological theory can be directly integrated into the estimation process to determine the mechanisms responsible for variation in observed survival rates. The relationship between predator functional response and prey survival offers a flexible and robust method to advance our understanding of predator-prey interactions in many complex natural systems where prey populations are marked and regularly visited.     

Interaction of Heliothis armigera nuclear polyhedrosis viral capsid protein with its host actin

In order to find the cellular interaction factors of the Heliothis armigera nuclear polyhedrosis virus capsid protein VP39, a Heliothis armigera cell cDNA library was constructed. Then VP39 was used as bait. The host actin gene was isolated from the cDNA library with the yeast two-hybrid system. This demonstrated that VP39 could interact with its host actin in yeast. In order to corroborate this interaction in vivo, the vp39 gene was fused with the green fluorescent protein gene in plasmid pEGFP39. The fusion protein was expressed in the Hz-AM1 cells under the control of the Autographa californica multiple nucleopolyhedrovirus immediate early gene promoter. The host actin was labeled specifically by the red fluorescence substance, tetramethy rhodamine isothicyanete-phalloidin. Observation under a fluorescence microscopy showed that VP39, which was indicated by green fluorescence, began to appear in the cells 6 h after being transfected with pEGFP39. Red actin cables were also formed in the cytoplasm at the same time. Actin was aggregated in the nucleus 9 h after the transfection. The green and red fluorescence always appeared in the same location of the cells, which demonstrated that VP39 could combine with the host actin. Such a combination would result in the actin skeleton rearrangement.     

The role of intra-specific mechanisms and predation in regulating the numbers of the lime aphid,Eucallipterus tiliae L.

Summary Analysis of changes in numbers of the lime aphid, Eucallipterus tiliae L., reveals that there is an overcompensated density dependent factor acting within years, and an inverse density dependent factor acting between years. Because of its effect on the aphid's rate of development and reproduction the variation in temperature from year to year acts as a density disturbing factor.There is no evidence from laboratory experiments to suggest that the quality of its food influences the numbers of the lime aphid. However, qualitative changes in the aphid following period of aphid abundance are shown to be important in the overcompensated density dependent response. The more prevalent insect predators influence the regulating process as they eat most of the aphids that remain after an aphid population has declined from a very high level of abundance. Their action results in a more overcompensated response than would occur in their absence.     

The polerovirus minor capsid protein determines vector specificity and intestinal tropism in the aphid

Aphid transmission of poleroviruses is highly specific, but the viral determinants governing this specificity are unknown. We used a gene exchange strategy between two poleroviruses with different vectors, Beet western yellows virus (BWYV) and Cucurbit aphid-borne yellows virus (CABYV), to analyze the role of the major and minor capsid proteins in vector specificity. Virus recombinants obtained by exchanging the sequence of the readthrough domain (RTD) between the two viruses replicated in plant protoplasts and in whole plants. The hybrid readthrough protein of chimeric viruses was incorporated into virions. Aphid transmission experiments using infected plants or purified virions revealed that vector specificity is driven by the nature of the RTD. BWYV and CABYV have specific intestinal sites in the vectors for endocytosis: the midgut for BWYV and both midgut and hindgut for CABYV. Localization of hybrid virions in aphids by transmission electron microscopy revealed that gut tropism is also determined by the viral origin of the RTD.     

Relationship between prey availability and population dynamics of the Eurasian lynx and its diet in northern Belarus

The diet and population dynamics of the Eurasian lynxLynx lynx Linnaeus, 1758 as well as an index of its main prey abundance were studied in transitional mixed forests of northern Belarus in 1985-2004. Monitoring of the lynx population and its main potential prey (the mountain hareLepus timidus, and the roe deerCapreolus capreolus) was done by snow-tracking. Also, abundance of tetraonids (Tetraonidae) was monitored by sight count. Hare numbers were fairly stable during the study period, whereas density of the roe deer population markedly increased, and tetraonids decreased. Composition of the lynx diet was stable seasonally. Lynx fed mostly on hares, roe deer and birds (usually tetraonids) year-round. However, the share of roe deer in lynx diet increased significantly during the period of its higher abundance and the share of tetraonids decreased with their decreasing numbers. There was also a remarkable increase of lynx population, which followed that of the roe deer, despite the pronounced decline of tetraonids. The results of the study emphasised the importance of roe deer as a prey of the Eurasian lynx.     

Tracking the role of alternative prey in soybean aphid predation by Orius insidiosus: a molecular approach

The soybean aphid, Aphis glycines (Hemiptera: Aphididae), is a pest of soybeans in Asia, and in recent years has caused extensive damage to soybeans in North America. Within these agroecosystems, generalist predators form an important component of the assemblage of natural enemies, and can exert significant pressure on prey populations. These food webs are complex and molecular gut-content analyses offer nondisruptive approaches for examining trophic linkages in the field. We describe the development of a molecular detection system to examine the feeding behaviour of Orius insidiosus (Hemiptera: Anthocoridae) upon soybean aphids, an alternative prey item, Neohydatothrips variabilis (Thysanoptera: Thripidae), and an intraguild prey species, Harmonia axyridis (Coleoptera: Coccinellidae). Specific primer pairs were designed to target prey and were used to examine key trophic connections within this soybean food web. In total, 32% of O. insidiosus were found to have preyed upon A. glycines, but disproportionately high consumption occurred early in the season, when aphid densities were low. The intensity of early season predation indicates that O. insidiosus are important biological control agents of A. glycines, although data suggest that N. variabilis constitute a significant proportion of the diet of these generalist predators. No Orius were found to contain DNA of H. axyridis, suggesting intraguild predation upon these important late-season predators during 2005 was low. In their entirety, these results implicate O. insidiosus as a valuable natural enemy of A. glycines in this soybean agroecosystem.