bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of temperature and leaf age on growth versus moulting time of a generalist caterpillar fed plantain (Plantago lanceolata)
Authors: STAMP N.E. , BOWERS M.D.
Published: March 2008

Abstract.

The simultaneous effects of daytime temperature (20°C versus 30°C) and leaf age (new versus intermediate‐aged) on a generalist insect herbivore were examined. Fourth‐instar Spilosoma congrua caterpillars were tested on plantain (Plantago lanceolata), one of this lepidopteran species’host plants, for which the major defensive chemicals, iridoid glycosides (aucubin and catalpol), could be quantified.

Cool temperature depressed amount of food eaten, amount of frass, and consumption and growth rates, and increased the proportion of time spent in the non‐feeding period (from head‐capsule slippage to ecdysis).

Average iridoid glycoside concentration was 2.8% dry weight (d.w.) in new leaves and 1.6% d.w. in intermediate‐aged leaves. When fed new leaves, the caterpillars had a higher efficiency of conversion of ingested food to biomass and a higher growth rate than those fed intermediate‐aged leaves. Furthermore, the proportion of time spent in the non‐feeding period was prolonged by a diet of intermediate‐aged leaves.

A second experiment showed that the percentage dry weight of aucubin, catalpol and total iridoid glycosides increased over 24 h in incubated, excised leaves, which meant that the caterpillars in the first experiment experienced somewhat higher iridoid glycoside concentrations than the levels in fresh leaves.

Overall, these results indicate that this generalist should prefer new plantain leaves over older leaves even though new leaves contain higher concentrations of iridoid glycosides.
Time‐lags in insect response to plant productivity: significance for plant‐insect interactions in deserts
Authors: AYAL YORAM
Published: March 2008

Abstract.

The interactions between the univoltine mirid bug Cupsodes infuscatus and its food plant, the geophyte Asphodelus ramosus, were studied in the Negev desert for a 5 year period. The bug feeds mainly on Asphodelus inflorescence meristems, flowers and fruits, and in some years may destroy more than 95% of the plant population expected fruit production.

Asphodelus expected fruit production fluctuated widely during the study period, but was not related to precipitation. Cupsodes density was related to the plant expected fruit production, but with a 1 year time lag. In years of high inflorescence production, a high per‐capita reproduction of the bug resulted in a dense bug population in the following year. This dense population then decimated the plant fruit production, became food limited and had a low per‐capita reproduction.

This kind of time lag is expected to be common among desert insect herbivores that specialize in using ephemeral resources. The rare years of high plant production are in general preceded and followed by years of low plant production. Hence, in years which contribute most to plant reserves (seed, underground storage organs), insect herbivores are relatively rare as a result of food limitation in preceding low production years. But the insect populations which build up during years of high plant production decimate their food resources and become food limited in subsequent years with low plant production.

Thus, herbivorous insects seem to have a limited ability to affect plant population dynamics in desert ecosystems. In contrast, the potential appears to be much greater for herbivorous insects to be regulated by their food plants.
The role of leaf‐cutting ant workers (Hymenoptera: Formicidae) in fungus garden maintenance
Authors: BASS M. , CHERRETT J. M.
Published: March 2008

Abstract.

We studied the role of leaf‐cutting ant workers (Atta sexdens(L.) in fungus garden maintenance, by temporarily excluding workers from the garden. This increased its subsequent attractiveness, as expressed by an increase in the numbers of workers licking it.

The length of free mycelia on areas of the garden from which workers were excluded increased but was reduced again when workers were returned. Workers therefore removed hyphae from the garden surface.

The maximum‘isolation effect’was obtained by preventing ant access for 2–3 days, after which the effect declined. Removing staphylae from portions of garden kept ant‐free for 4 and 6 days restored the effect, as the ants were not distracted by harvesting staphylae. Portions of garden kept ant‐free for longer than this were no more attractive than non‐isolated control garden.

Workers were highly efficient in detecting and removing contaminants from their fungus garden. Samples of garden could be isolated from workers for up to 12 days before major growth of contaminants occurred, and this contrasted with the maximum of 6 days for the isolation effect on licking. The isolation effect was therefore not a response to contaminant growths on the garden.

Workers on the garden surface may remove hyphae for nutritional reasons, or to‘prune’their fungus and stimulate its growth. In either case, the result is a regulation of fungal growth.
Geographic variation in reproductive success of the parasitoid Asobara tabida in larvae of several Drosophila species
Authors: KRAAIJEVELD ALEX R. , VAN DER WEL NICOLE N.
Published: March 2008

Abstract.

Asobara tabida is a parasitoid of Drosophila larvae in fermenting substrates. Because it is a widespread species, it may encounter different biotic and abiotic circumstances in various parts of its range.

The species composition of the host population varies over the parasitoid's range: D.obscura‐group species (especially D.subobscura) are the main hosts for northwestern and central European parasitoids; D.melanogaster is the main host for southern European parasitoids.

D.melanogaster larvae can defend themselves against A.tabida by encapsulating the parasitoid egg, and survival in D.melanogaster is always lower than in D.subobscura.

Parasitoids from southern European populations are much better able to survive in D.melanogaster than their northwestern and central European conspecifics; parasitoids from different populations are equally well able to survive in D.subobscura.

The lower survival in D.melanogaster may be partly compensated for by the larger size of parasitoids emerging from this host species compared to parasitoids emerging from D.subobscura.

Within population groups, larger A.tabida females have more eggs in their ovarioles. Additionally, southern European females have more eggs and less fat than northern and western/central European females. The relationship between size and longevity is ambiguous.

It is concluded that parasitoids from different populations are adapted to region‐specific circumstances.
Genotype and environment interact to influence acceptability and suitability of white spruce for a specialist herbivore, Zeiraphera canadensis
Authors: QUIRING D. T. , BUTTERWORTH E. W.
Published: March 2008

Abstract.

The independent and interacting effects of plant genotype and site (i.e. environment) on the acceptability of white spruce, Picea gluaca (Moench) Voss, to the spruce bud moth, Zeiraphera canadensis Mut. & Free. and on plant suitability for egg development, were studied at four sites in New Brunswick, Canada.

A greater proportion of shoots on trees in two half‐sib families, previously designated as highly susceptible, were partially eaten by spruce bud moths than shoots on trees in two half‐sib families with low susceptibility.

At the site with the highest bud moth population, oviposition was highest on trees in susceptible families and on branches damaged by bud moth larvae. Oviposition was not higher on trees in susceptible families at the other three sites, resulting in a strong tree genotype × site interaction for oviposition.

Although there was a significant tree genotype × site interaction for egg predation, egg survival was higher on trees in susceptible families at all sites, due to lower levels of egg parasitism and predation.

Egg densities were positively but weakly correlated to shoot length and diameter. There were no consistent relationships between shoot length, shoot diameter, needle length or needle density and per cent egg survival, parasitism or predation.

Because egg survival was higher on trees in susceptible families at all sites but egg densities were only higher on trees in susceptible families at one site, host plant acceptability and suitability were positively related at only one site. We speculate that Z.canadensis does not distinguish between hosts of different suitability until trees are heavily damaged.
The superiority of bumblebees to honeybees as pollinators: insect visits to raspberry flowers
Authors: WILLMER P. G. , BATAW A. A. M. , HUGHES J. P.
Published: March 2008

Abstract.

The behaviour and activity patterns of Apis mellifera and of five species of Bombus were analysed in relation to climatic variables and nectar quality on three varieties of unsprayed cultivated raspberry (Rubus idaeus) in eastern Scotland.

Stages of floral morphology and reward were similar for the three varieties: young flowers offered both nectar and pollen, but medium and old flowers offered nectar only, in diminishing quantities.

A wide range of insects visited raspberry flowers, but bees were dominant, bumblebees being responsible for about 60% of all visits and honeybees making up most of the remaining percentage. All bees had substantial pollen deposited on their bodies during visits, though few specifically collected it.

Bombus spp. were found to favour young (receptive) flowers strongly, especially early in the morning when pollen was most abundant: whilst Apis visited unselectively. Bumblebees also foraged over substantially longer periods of the day, and in poorer weather, some being present at most times of observation; and they foraged more quickly in terms of flower visits per minute.

Bombus carried more pollen on their bodies than Apis, and also deposited more pollen on raspberry stigmas, with B.lapidarius and B.terrestris being particularly effective and also being the most abundant species. All bumblebees also foraged over a longer range, moving between canes and rows more frequently than did honeybees.

Bumblebees are therefore likely to be substantially more important as pollinators of raspberries than are honeybees, especially as raspberries though moderately self‐fertile may exhibit metaxenia. Reasons why Bombus may be the preferred pollinator in most sites of raspberry cultivation are discussed, together with implications for present and future growers.
Persistent size variation in the anthophorine bee Centris pallida (Apidae) despite a large male mating advantage
Authors: ALCOCK JOHN
Published: March 2008

Abstract.

Despite apparent directional sexual selection in favour of large body size, males of the anthophorine bee Centris pallida remain highly variable in body size.

One possible cause of persistent size variation among males is geographic variation in the extent of the large male mating advantage. However, a study of a population in an area not previously investigated revealed that the large male mating advantage was as strong here as it has been elsewhere in other years.

Although the reproductive benefits of being large were consistent in populations separated spatially and temporally, the intensity of bird predation on mate‐searching males varied greatly between locations.

The bee‐killing birds focused exclusively on bees which were digging down to meet emerging females or fighting on the ground, never on flying males. Males which were collected on the ground by hand (to simulate avian predation) were significantly larger on average than flying males collected by sweep netting.

Therefore, in some location in some years, sexual selection in favour of large body size may be opposed by natural selection exerted by predators, perhaps contributing to the maintenance of size variation in this bee.
Direct and indirect effects of plant genetic variation on enemy impact
Authors: FRITZ ROBERT S.
Published: March 2008

Abstract.

The Tritrophic and Enemy Impact concepts predict that natural enemy impact varies: (a) among plant genotypes and (b) may depend on the abundance of heterospecific herbivores, respectively. I tested these predictions using three herbivore species on potted, cloned genotypes of Salik sericea Marshall in a common garden experiment.

Densities of the leaf miner (Phyllonorycter salicifoliella (Chambers)) and two leaf galling sawflies (Phyllocolpa nigrita (Marlatt) and Phyllocolpa eleanorae Smith and Fritz) varied significantly among willow clones, indicating genetic variation in resistance.

Survival and natural enemy impact caused by egg and larval parasitoids and/or unknown predators differed significantly among willow clones for each of the three herbivore species, indicating genetic variation in survival and enemy impact.

Survival of Phyllonorycter was negatively density‐dependent among clones.

Survival of Phyllonorycter and Phyllocolpa eleanorae were positively correlated with densities of heterospecific herbivores among clones and parasitism of these species were negatively correlated with densities of the same heterospecific herbivores among clones.

At least for Phyllonorycter this positive correlation may suggest either facilitation of survival between herbivore species, which do not share natural enemies, or an apparent interaction caused by host plant genetic variation.

Among clones, egg parasitism of Phyllocolpa eleanorae was weakly positively correlated with density of Phyllocolpa nigrita. Since these species share the same Trichogramma egg parasitoid, this interaction could support the hypothesis of apparent competition.
Squash beetle trenching behaviour: avoidance of cucurbitacin induction or mucilaginous plant sap?
Authors: McCLOUD E. S. , TALLAMY D. W. , HALAWEISH F. T.
Published: March 2008

Abstract.

Foraging patterns of the squash beetle, Epilachna borealis Fabricius (Coleoptera: Coccinellidae), in field cages are not consistent with the hypothesis that this beetle avoids leaves in which its feeding damage has caused the induction of cucurbitacins.

E.borealis feeding does not induce accumulation of cucurbitacins inside or outside of feeding trenches.

Cucurbitacins do not reduce the survival or growth rate of E. borealis larvae.

High concentrations of cucurbitacins fail to deter E.borealis feeding; rather, cucurbitacins are feeding stimulants for squash beetles.

Trenching behaviour in E.borealis is facultative and correlates with leaf turgor and the degree to which sticky phloem sap oozes from damaged leaves.

Mucilaginous phloem sap in many curcurbit species inhibits feeding by E.borealis when it is applied to beetle mouthparts.
Population suppression for control of the blowfly Lucilia sericata and sheep blowfly strike
Authors: WALL R. , FRENCH N. P. , MORGAN K. L.
Published: March 2008

Abstract.

The control of ovine myiasis by suppression of populations of the blowfly Lucifia sericata was investigated experimentally on three farms in the south‐west of England in 1992 and 1993.

In blind trials, sheep on one farm (control) were given two doses of placebo, on a second two doses of the larvicide cyromazine (Vetrazin®, CibaGeigy), and on a third cyromazine and a subsequent dose of placebo.

The first treatment was given shortly before the predicted spring emergence of L.sericata and the second shortly before the predicted emergence of the second generation. Previous simulation analysis had identified strategic early‐season treatment as the optimum for blowfly population suppression.

On both treatment farms significantly smaller L.sericata populations were recorded throughout 1992 and the incidence of strike was significantly lower than on the control farm. The results show that appropriate early‐season timing of sheep treatment can suppress populations of L.sericata and could be used by farmers to reduce the incidence of blowfly strike.

The results suggest, however, that the effectiveness of population suppression and strike incidence may have been influenced by immigration into the control areas and by adverse weather, the latter changing the susceptibility of sheep to strike and resulting in rising strike incidence even when L.sericata population densities were low. In practice, therefore, blowfly population suppression should be employed as a component of an integrated strike management programme.
A new inexpensive suction apparatus for sampling arthropods in grassland
Authors: STEWART ALAN J. A. , WRIGHT ANN F.
Published: March 2008

Abstract.

We describe a new technique for sampling arthropods from grassland and other vegetation, using a modified petrol‐driven suction apparatus called a‘Blow & Vac’.

The new apparatus was tested by comparing its efficiency in extracting arthropods from vegetation with that of a conventional Dietrick, or‘D‐Vac’, suction sampler.

Unimpeded air velocity inside the suction tube was approximately 4 times that of the D‐Vac.

In field trials on semi‐natural grasslands, the Blow & Vac caught more individuals of most spider and certain beetle species compared to the D‐Vac and approximately equal numbers of Auchenorrhyncha.

We conclude that the‘Blow & Vac’has considerable potential for sampling arthropod populations. Its low cost and weight make it a suitable alternative to the conventional D‐Vac apparatus.
The biology of the phonotactic parasitoid, Homotrixa sp. (Diptera: Tachinidae), and its impact on the survival of male Sciarasaga quadrata (Orthoptera: Tettigoniidae) in the field
Authors: ALLEN GEOFF R.
Published: March 2008

Abstract.

Unlike most parasitoids, tachinid flies of the tribe Ormiini use sound to locate their hosts. Although thought to exert selection pressure on their host's calling behaviour, little is known about the biology of ormiines. Accordingly, this study reports the biology and impact of the ormiine Hornotrixa sp. upon calling males of the univoltine bushcricket Sciarasaga quadrata Rentz in south‐western Australia.

Populations of adult S.quadrata were monitored in the field over two successive calling seasons. Females, which do not call, were not parasitized by Hornotrixa sp., but the risk of parasitism for males increased as the 3‐month calling season progressed. Parasitism did not commence until c. 2 weeks into the calling season, but by the end of the season up to 87% of surviving males were parasitized.

Parasitized males lived for 14 days and were found singing until their penultimate evening before death in the field. Unparasitized males lived on average 69 days and a maximum of 119 days.

Multiparasitism of hosts was common, with up to sixteen fly larvae found within parasitized males. The number of fly larvae within hosts significantly increased at the end of the season. However, successful emergence of fly larvae from hosts, as well as pupal size, significantly decreased as more than one fly larva developed within the host.

Hornotrixa sp. has a long pupal duration of 30–31 days at 20°C. As a consequence, only one complete fly generation, which overwinters in the pupal stage, is likely within each host generation.

No evidence for differential (size‐bias) mortality by Hornotrixa sp. on male S.quadrata was found. The size of parasitized and unparasitized males collected in the field was not significantly different.

It is concluded that Hornotrixa sp. is a significant mortality factor acting on the survival of adult male S.quadrata.
Body size distribution in aphids: relative surface area of specific plant structures
Authors: DIXON A. F. G. , KINDLMANN P. , JAROŠIK V.
Published: March 2008

Abstract.

The distribution of the body sizes of British aphids is right‐skewed on a logarithmic axis, as in other taxa. Over the size range 2–5 mm there is a marked decrease in numbers of species with increase in size, which on a log log scale has an exponent of ‐3, The exponent for the right‐hand side of the size distribution of British plants is ‐0.7.

The sizes of sixty‐eight species of the genusAphisare weakly correlated with the size of their respective host plants.

An aphid's size is strongly correlated with the length of its proboscis, which indicates the depth to which it has to probe plant tissues in order to feed.

On average, trees host more species of aphids than either shrubs or herbaceous plants, which appears to be associated with the relative surface area of specific plant structures. The surface area of plants is mainly made of leaves and most species of aphids are leaf feeders. The largest and least numerous species of aphids feed on the branches and trunks of trees, the proportional cover of which is less than that of leaves.

Taking into account all the above observations, a functional explanation in terms of the relative surface area of specific plant structures is offered to account for the size diversity curve of aphids.
Philopatry in the alpine grasshopper, Podisma pedestris: a novel experimental and analytical method
Authors: MASON P. L. , NICHOLS R. A. , HEWITT G. M.
Published: March 2008

Abstract.

Local dispersal and philopatric behaviour of the alpine grasshopper, Podisma pedestris, were studied at two sites in the Alpes Maritimes using a new mark—release—resight technique featuring marking in situ, and multiple resighting without handling. The time‐consuming nature of the design was justified by the quantity and quality of the data yielded.

Philopatry is defined independently of any concept of home range as a phenomenon by which movements over longer periods are less than would be expected by extrapolation of measures over shorter periods.

By this definition, the grasshoppers are shown to exhibit philopatry. Nymphs comprise two heterogenous classes of those which move little and those which move considerable distances.

Daily dispersal estimates were obtained from movements of 1055 nymphs and adults at one site, and of 593 adults at another.

Differences are demonstrated in daily dispersal distances for age, sex and site combinations.

Some differences in microhabitat preference were observed.

The findings are compared with previous measurements of dispersal in this species, and the merits of the new technique are discussed.
Variable chemical defence in the checkerspot butterfly Euphydryas gillettii (Lepidoptera: NymphaIidae)
Authors: BOWERS M. DEANE , WILLIAMS ERNEST H.
Published: March 2008

Abstract.

Like other checkerspots, Euphydryas gillettii butterflies may contain the defensive chemicals, iridoid glycosides, which are sequestered from their hostplants during larval feeding.

We analysed the iridoid glycoside content of E.gillettii adults from two different populations, Warm Lake, Idaho, and Granite Creek, Wyoming, that have different patterns of hostplant use.

Gas chromatographic analysis of thirty butterflies from the Wyoming population showed that they contained a mean of 1.27 (±0.19 SE) % dry weight iridoid glycosides. Notably, 20% of these butterflies contained no detectable iridoid glycosides.

In contrast, nineteen butterflies from the Idaho population contained a mean of 3.89 (±0.38 SE) % dry weight iridoid glycosides, and all butterflies contained iridoid glycosides.

These results illustrate how the chemical defence of herbivorous insects varies according to differential use of potential hostplants.
Impacts of defoliation by tussock moths (Orgyia vetusta) on the growth and reproduction of bush lupine (Lupinus arboreus)
Authors: HARRISON SUSAN , MARON JOHN L.
Published: March 2008

Abstract.

Outbreaks of tussock moths (Orygia verusta Bdv.) on bush lupines (Lupinus arboreus Sims) may be very intense, although spatially localized, and may last >10 years. To understand better how such outbreaks may persist, we defoliated lupine bushes using variable realistic numbers of tussock moth larvae, and measured the immediate and delayed impacts of defoliation on the growth and seed production of lupine bushes.

Immediate effects of defoliation included the production of new leaves that were significantly smaller in diameter and biomass, and lower in water content, than the new leaves of undamaged bushes. Also, seed output was reduced by up to 80% on heavily damaged bushes.

In the longer term, surviving bushes recovered remarkably well, despite having received the full range of possible (survivable) insect densities. After 1 or 2 years’rapid growth, surviving bushes were not affected in terms of height, basal stem diameter or volume by their previous defoliation. However, there was a significant tendency for juvenile bushes to produce more seeds the more heavily they had been attacked the previous year.

The ability of the host plant to recover, in terms of its biomass, helps to explain the sustained nature of the insect outbreak.
Effects of temperature on phenological synchrony and altitudinal distribution of jumping plant lice (Hemiptera: Psylloidea) on dwarf willow (Salix lapponum) in Norway
Authors: HILL JANE K. , HODKINSON IAN D.
Published: March 2008

Summary.

The geographical distributions of three species of jumping plant lice (psyllids) along an altitudinal transect (988–1300 m a.s.l.) in southern Norway were restricted within the range of their host plant Salix lapponum. One species, Cacopsylla propinqua, occurred at all sampling locations between 988 and 1222 m, whereas C.palmeni was confined to higher altitudes (1153–1222 m) and C.brunneipennis was more abundant at lower altitudes (988–1101 m).

C.brunneipennis and C.palmeni developed only on female catkins. Development times of catkins and psyllids were similar (approximately 50 days) and successful psyllid development depended on close phenological synchrony with catkins.

Thermal requirements for development of female catkins were greater at low altitude (988 m) compared with higher altitude (1222 m), showing local adaptation of S.lapponum to altitude. In general, thermal requirements of psyllids were less than those of catkins at the same location. C.brunneipennis had higher thermal requirements than C.palmeni.

Field experiments, using polythene enclosures to elevate temperatures at two sites at different altitudes (by 0.6–1.4 deg. C), showed that insects had an enhanced relative rate of development under elevated temperatures compared with their host plants.

Indices of phenological synchrony were calculated from thermal requirements of psyllids and catkins. Under elevated temperatures, phenological synchrony decreased at both sites. This resulted in the subsequent development of smaller adult insects at low altitude, although at higher altitude, insects developing under elevated temperatures were larger and had a higher survival rate compared with controls.

Effects of temperature on phenological synchrony may explain the limits to the geographical range of psyllids. The consequences of climate change on psyllid populations will depend on the effects of decreased phenological synchrony on insect development and this may differ within the insect's geographical range.
Colony founding in the primitively eusocial wasp,Ropalidia marginata(Hymenoptera: Vespidae)
Authors: SHAKARAD MALLIKARJUN , GADAGKAR RAGHAVENDRA
Published: March 2008

Abstract.

In a 16‐month study in Bangalore, India, about 35% of the newly founded colonies ofRopalidia marginatawere single foundress colonies and the remainder were multiple foundress colonies with two to twenty‐two individuals.

Larger colonies did not have a significantly higher per capita productivity, did not produce significantly heavier progeny and did not produce them significantly faster than smaller colonies did.

Predation by the hornetVespa tropicaappeared to be independent of group size.

Single foundress colonies failed more often but not often enough to make them have a lower average per capita productivity, compared to multiple foundress colonies.

Some of the advantages of multiple foundress associations came from the greater predictability of their attaining the mean per capita productivity, the relatively lower rates of usurpation experienced by them compared to single foundress colonies, and the opportunities provided by queen turnovers for workers to become replacement queens and gain direct individual fitness.
Direct and indirect effects of a predatory backswimmer (Notonecta maculata) on community structure of desert temporary pools
Authors: BLAUSTEIN LEON , KOTLER BURT P. , WARD DAVID
Published: March 2008

Abstract.

We assessed experimentally the effects of the predatory backswimmer, Notonecta maculata, on naturally colonizing mosquito populations in artificial outdoor pools in the Negev Desert, Israel. A single Notonecta adult per pool (8–15 litres water) had a very large negative impact on populations of Culiseta longiareolata, the most common species found in natural local pools. Notonecta caused large reductions of Culiseta egg rafts and early‐instar larvae (instars I and II) and virtually 100% reductions of late‐instar Culiseta larvae (instars III and IV) and pupae.

Notonecta also caused a trophic cascade in the experimental pools; by preying on periphyton‐feeding Culiseta larvae, Notonecta indirectly caused significantly higher densities of diatoms, the major component of the periphyton.

Surveys of nearby natural pools taken between March and May supported the experimental results: a strong negative association between Notonecta and Culiseta among pools occurred as Notonecta increased in numbers and became more widely distributed. Anopheles (occurring only in May) and Culex mosquito immatures were not negatively associated with Notonecta. Culiseta was not associated with surface vegetation whereas both Culex and Anopheles showed strong positive associations with surface vegetation both among and within pools. We attribute the negative association between the predator and Culiseta to local prey extinctions caused by Notonecta in individual pools. Culiseta, being an open water species, is apparently more prone to predation by Notonecta than the vegetation‐dwelling Culex and Anopheles.
Potential rates of Increase of solitarious and gregarious phases of the African armyworm Spodoptera exempta (Lepidoptera: Noctuidae)
Authors: CHEKE ROBERT A.
Published: March 2008

Abstract.

The African armyworm Spodoptera exempta exhibits a phase polyphenism with insects capable of transforming from one‘phase’to another, which involves both physiological and behavioural changes. Amongst these changes, evidence from the laboratory and the field suggest that, given equivalent conditions of temperature and food, solitary phase insects take longer to complete their life cycles than gregarious phase insects, and the latter's generations are more synchronized. There is also some evidence that females of the solitary form sometimes lay more eggs.

Using data from field and laboratory studies, estimates of the rates of increase of each form were calculated from Leslie matrix models. Assuming equivalent mortality rates for both phases, asynchronous development for the solitaries and synchronous development for the gregarious forms, with the latter having lower fecundities than the solitaries, the models suggest that the gregarious forms have higher values of their intrinsic rates of increase (r) than solitarious populations. These results are explored using a range of parameter values including variation in the percentage of solitaries with delayed development.

The possible ecological and evolutionary significance of variations in rates of increase of gregarious and solitary populations are briefly discussed.
Interspecific host discrimination and competition inApoanagyrus (Epidinocarsis) lopeziandA.(E.)diversicornis, parasitoids of the cassava mealybugPhenacoccus manihoti
Authors: PIJLS JANINE W. A. M. , HOFKER KEES D. , STAALDUINEN MARTIN J. VAN , ALPHEN JACQUES J. M. VAN
Published: March 2008

Abstract.

Choice experiments on interspecific host discrimination inA.lopeziandA. diversicorniswere carried out on discs of cassava leaf containing four hosts (P.manihoti) that had been parasitized by the other species and four unparasitized hosts.

A.lopeziaccepted both host types equally for oviposition, whereasA.diversicornisaccepted fewer hosts that had been parasitized byA.lopezithan unparasitized ones.A.diversicornisis therefore capable of interspecific host discrimination, but such a capability was not demonstrated forA.lopezi.

Survival probability in singly parasitized hosts was 0.85 for both parasitoid species. When the time interval between ovipositions was 2 h or less, survival in multiparasitized hosts was 0.68 forA.lopeziand 0.17 forA.diversicornis, irrespective of priority. IncreasingA.lopezipriority to 24±2h did not increaseA.lopezisurvival.A.diversicornissurvival, however, increased to 0.43 whenA.diversicorniswas given 24 ± 2 h priority.A.diversicorniseggs took 19 h longer thanA.lopezieggs to hatch. This could explain the difference in competitive abilities in multiparasitized hosts.

The observed difference in host selection behaviour betweenA.lopeziandA.diversicornisis in accordance with the different benefits of multiparasitism:A.lopezigains more thanA.diversicornisbecause of its superior within‐host competitive abilities.

Neither species avoided multiparasitism completely. The low survival probability ofA.diversicornisin multiparasitized hosts may partly explain its failure to establish when introduced into Africa as part of a biological control programme ofP.manihoti.
Diapause, migration and pyrethroid‐resistance dynamics in the cotton bollworm, HeIicoverpa armigera (Lepidoptera: Noctuidae)
Authors: SOUZA KENNETH DE , HOLT JOHNSON , COLVIN JOHN
Published: March 2008

Abstract.

A diapause induction and duration experiment was conducted in the laboratory on Indian Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) where 79% of individuals had extended pupal periods. At 22°C and 26°C respectively, 57% and 100% of the pupae had emerged 145 days after pupation.

A mathematical model was developed to investigate the interactions between diapause, migration and pyrethroid resistance frequency development in both eastern Australia and Andhra Pradesh, India.

The effect of diapause was different in the Australian and Indian cases, providing a mechanism to conserve resistance and susceptibility respectively.

For Australia, the model simulated discriminating dose data reasonably well and showed that resistance frequencies could rise prior to the pyrethroid window without invoking cross‐resistance to non‐pyrethroid insecticides applied to cotton.

The saw‐toothed seasonal cycle of resistance development could be simulated in the Indian case without hypothesizing the existence of susceptible migrants.

The implications of‘refugia’populations for H.armigera insecticide resistance management programmes are discussed.
Structural refuges in two stem‐boring weevils onRumex crispus
Authors: FREESE GUNTER
Published: March 2008

Abstract.

Differences in feeding positions, parasitoid complexes and parasitization rates of the two dominant insect species in stems ofRumex crispuswere investigated.Apion miniatum(inhabiting the lower 10% of the stem) andApion violaceum(occurring all along the stem) exploited distinctly different feeding positions, partly due to differences in time of oviposition.

A.miniatumsuffered less parasitization thanA.violaceum, measured both by number of parasitoid species and parasitization rates. Its feeding position constitutes a refuge.

Parasitization ofA.violaceumwas least in individuals feeding in basal, thick parts of the stem. There is a trend that the developed refuge increases with increasing stem diameter.

The refuge ofA.violaceumin basal positions only affected idiobiont ectoparasitoids, because koinobiont endoparasitoids attack the weevils before they enter the stem. Moreover, the koinobiont did benefit from the refuge itself by avoiding hyperparasitism.

Densities ofA.violaceumincreased with plant size, whereas percentage parasitism did not differ. Its three most abundant parasitoid species showed small‐scale density‐independent patterns of attack over all plants. Therefore a constant proportion of weevil larvae mine within the refuge independent of its potential size.

Synchronization between weevils and plants, as well as between parasitoids and hosts, appears to be the dominant factor for the spatial community structure of the stem borersof Rumex crispusand their enemies.
The influence of diet on growth and secretion behaviour of myrmecophilous Polyommatus icarus caterpillars (Lepidoptera: Lycaenidae)
Authors: BURGHARDT FRANK , FIEDLER KONRAD
Published: March 2008

Abstract.

Caterpillars of the facultatively myrmecophilous butterfly Polyommatus icarus were reared on inflorescences, or foliage, of four natural hostplant species and on an artificial diet to study dietary effects on larval growth and secretory capacity.

Caterpillars achieved highest weights and relative growth rates when fed flowers of Medicago sativa, Lotus corniculatus or Melilotus officinalis. Larvae reared on Coroniüa varia (flowers and leaves), foliage of M.sativa and on the artificial diet pupated at lower weights and achieved lower growth rates.

In standardized experiments with the ant species Lasius flavus, secretion rates from the dorsal nectar organ (DNO) were 2 times higher among flower‐fed caterpillars than among foliage‐fed siblings or caterpillars on the artificial diet. Larvae reared on C.varia flowers were superior to all other food treatments with respect to secretion rates.

High water content of larval diet, as in flowers, appears to be important for lycaenid caterpillars to achieve high secretion rates, whereas the correlation between myrmecophily and nutrient availability, as evidenced by growth rates, was less pronounced.

Using experimental data on larval growth and secretion rates, the lifetime volume of secretions from the DNO is estimated to range from 2 to 5 μl in most food treatments. Only on C.varia flowers (5.5–8.7 μl) and on M.sativa leaves (0.9–1.1 μl) did the caterpillars deviate in their absolute investment in myrmecophily.

The estimated lifetime investment accounted for 1.6–5.5% of prepupal fresh weight in all food treatments except on C.varia flowers (7.8–12.3%).
Carabid life‐cycle strategies and climate change: a study on an altitude transect
Authors: BUTTERFIELD J.
Published: March 2008

Abstract.

There was little overlap in the species composition of carabid beetle assemblages sampled below 450 m and above 800 m on an altitude transect and the first axis of a DECORANA ordination was closely correlated with altitude (r11= 0.93, P < 0.001), probably reflecting the differing temperature requirements of different species.

Life‐cycle strategies of two low‐altitude species, found predominantly below 600 m, and two species caught above 600 m a.s.l., have been determined, using mandible wear to identify whether the females breed in the calendar year that they emerge as adults or in the year following.

Nebria salina has an annual cycle at 630 m. Pterostichus madidus and Calathus fuscipes were both biennial at altitudes above 300 m although predominantly annual at low altitude. N.gyllenhali was biennial above 600 m and it is not known whether it is able to switch to an annual cycle at low altitude.

Both N.salina and N.gyllenhali ceased activity soon after emergence, an adaptation which preserves their mandibles from wear.

At altitudes of 305 m and 430 m, P.madidus and C.fuscipes entered the breeding season with 33% and 56% reduction in mandible tip length, possibly reducing their reproductive output.

The necessity for relatively sharp mandibles on entry into the breeding season may restrict the capacity of carabids to respond to a temperature change by switching from annual to biennial cycles, and vice versa, adding support to the suggestion that carabids are more likely to respond to climate change by shifting distributions than by physiological adaptation.
Temporal changes in host adaptation in the pea aphid, Acyrthosiphon pisum
Authors: SANDSTRÖM JONAS
Published: March 2008

Abstract.

Temporal changes in host adaptation were followed in a local population of the pea aphid, Acyrthosiphon pisum. Aphid clones were collected in one alfalfa and one clover field at three different times. In the spring, first‐generation females were collected. Later, in the autumn, females belonging to the last parthenogenetic generation were collected. Lastly, sexual females were collected after mating in autumn and allowed to produce eggs which were hatched. The performance was evaluated on alfalfa and clover. The spring‐collected individuals were also assessed on peas.

On the overwintering hosts clover and alfalfa, the clones performed best on the plant of origin, i.e. negative correlations in performance. Correlations between performance on the temporary summer host, pea, and that on clover/alfalfa were weak or nonsignificant.

Significant variation in host performance was found within both host fields at spring, which is a prerequisite for changes in clone composition due to selection/migration.

The clones from alfalfa showed an increase in mean performance on alfalfa between spring and autumn, whereas no changes among the clones from the clover field were observed. This difference in seasonal response between the two fields could have been the result of larger variation in performance among the alfalfa clones and/or a differential tendency to migrate among clones in both fields.

After sexual recombination in the autumn, mean performance in the alfalfa field returned to the spring level, probably as a result of emergence of new genetic combinations. In the clover field, mean performance did not change significantly over time.
The window of vulnerability and its effect on relative parasitoid abundance
Authors: BRIGGS CHERYL J. , LATTO JOHN
Published: March 2008

Summary.1. The length of time that a gall‐forming midge,Rhopalomyia califomica, was vulnerable to attack by four parasitoid species was measured in the field at two locations.

2. The midge had a restricted window of vulnerability to each of the parasitoid species, but similar windows of vulnerability were found at the two sites.

3. A stage‐structured model was used to illustrate that the length of the vulnerable window should have no effect on the fraction parasitized by a single parasitoid species if that species is the only parasitoid attacking the host in a coupled host‐parasitoid interaction. However, the length of the window of vulnerability can have a positive effect on the fraction parasitized by a species in competition with other parasitoid species.

4. The length of the window of vulnerability can help explain the relative field abundance of four of the common parasitoid species ofR.californica.
Movement of an insect parasitoid in simple and diverse plant assemblages
Authors: COLL MOSHE , BOTTRELL DALE G.
Published: March 2008

Abstract. 1. It has been proposed that herbivore populations are lower in diverse than in simple plant habitats because of greater abundance and/or higher efficiency of natural enemies in mixed plant stands. However, higher enemy colonization is expected in monorather than multispecific vegetation if the response of specialist natural enemies to habitat diversification is similar to that of monophagous herbivores.

2. We used release‐recapture experiments to determine how the presence of maize (non‐host plant) influences the movement of the parasitoid Pediobius foveolatus in the absence of hosts. We then assessed how vegetation diversity affects wasp reproduction (parasitism) and subsequent density in the presence of its hosts, Mexican bean beetle larvae.

3. Fewer female wasps immigrated into and more emigrated out of a bean‐tall maize intercrop than bean monocultures. Bean plant density and the presence of maize per se did not significantly affect parasitoid immigration. Instead, maize height was the primary factor contributing to lower female immigration into the bean‐tall maize plots. However, tall maize plants did not impede the wasps' within‐habitat movement.

4. When wasps were released outside the plots, higher parasitism was recorded in monocultures, irrespective of host density. In contrast, when wasps were released within the plots, significantly higher parasitism rates were found in the bean‐tall maize habitat.

5. Results suggest that female wasps accumulate in the bean‐tall maize habitat in response to resources other than hosts and, ultimately, wasp density may be determined primarily by differential emigration rather than by immigration rates.
Impact of a natural enemy overwintering refuge and its interaction with the surrounding landscape
Authors: CORBETT ANDREW , ROSENHEIM JAY A.
Published: March 2008

1. Egg parasitoids in the genus Anagrus (Hymenoptera: Mymaridae) are important mortality factors for grape leafhoppers (Erythroneura elegantula; Homoptera: Cicadellidae) in California vineyards, yet must overwinter in habitats external to these vineyards. Existing evidence suggests that French prune trees, which harbour the overwintering host Edwardsiana prunicola, planted adjacent to vineyards may enhance early‐season abundance of Anagrus.

2. Anagrus overwintering in French prune tree refuges were labelled with the trace element rubidium in four separate experiments. Rubidium‐labelled Anagrus were captured in adjacent vineyards in two of the experiments, confirming that French prune trees contribute to early‐season Anagrus populations. Anagrus from refuges were captured at the most distant sampling positions, 100 m from refuges.

3. Use of rare element labelling has, for the first time, enabled the relative contribution of different sources to early‐season colonization by this parasitoid to be quantified. Refuges contributed 1% and 34% of Anagrus colonizing two of the experimental vineyards, respectively. The remainder originated from overwintering habitats external to the French prune/vineyard system.

4. The spatial patterns of Anagrus originating from external overwintering habitats suggest that the French prune trees are generating a ‘windbreak effect’. Anagrus dispersing within the windstream colonized vineyards at a higher‐than‐average rate immediately downwind of refuges.

5. The amount of colonization by Anagrus from external overwintering habitats was apparently related to the distance to presumed overwintering habitats. These findings demonstrate that both the number of natural enemies emerging from a refuge and the composition of the surrounding landscape are important in determining the impact of local, small‐scale habitat manipulations.
Post‐emergence migration of stoneflies (Plecoptera) into the nearby forest
Authors: KUUSELA KALEVI , HUUSKO ARI
Published: March 2008

Abstract. 1. The post‐emergence lateral migration of both sexes of eight stonefly species was examined in a dystrophic, fourth‐order forest river in eastern Finland.

2. For this purpose, 7351 stonefly adults were collected with eighteen trunk funnels positioned in rows of six at distances of approximately 1, 15 and 60 m from the river. A further 1880 adults were also caught from the vegetation of the bank zone by sweep netting and with slit traps.

3. The species could be grouped into two types with respect to migration distance: Isoperla difformis, I.grammatica and Leuctra fusca tended to stay in the bank area, whereas Nemoura flexuosa, N.avicularis, Amphinemura borealis, L.hippopus and N.cinerea tended to disperse into the forest, so that the majority were found some distance away from the shore.

4. The males of the leuctrids, N.flexuosa and N.cinerea migrated farther than the females.

5. The sex ratio was significantly biased in all species except N.flexuosa. The isoperlids, leuctrids and A.borealis showed a significant predominance of females in the trunk funnel catches, but males were significantly dominant in N.avicularis and N.cinerea. The material caught by other methods reversed the ratio for I.difformis and N.avicularis. Comparison of the sex ratios of the species with other reports revealed marked variation and deviation from unity, much of which could be attributed to bias introduced by the sampling methods.

6. Lateral migration seems to be the first phase in the colonization cycle, although the latter as such was not studied here. Adults of Euholognatha species migrate farther than those of Systellognatha, a difference of which may be due to their ability to feed as adults.