Water balance in Collembola and its relation to habitat selection; cuticular water loss and water uptake

In the order Collembola a clear relationship was found between overall cuticular water loss and water conditions of the habitat. The different transpiration rates were negatively correlated with the haemolymph osmotic pressure, but there was no clear causal relationship. In two species, Orchesella cincta and Tomocerus minor, which live sympatric but have a different micro-distribution (partly due to small scale heterogeneity in water conditions), important differences exist both in rate of water loss and in speed of water uptake: Orchesella cincta had a significantly lower transpiration and a higher speed of water uptake than Tomocerus minor. The transpiration rates of both species were linearly related to the vapour pressure deficit of the ambient air. Contrary to Orchesella cincta, Tomocerus minor lost water in saturated conditions. Freshly-killed Orchesella cincta had a higher transpiration rate than living individuals, but in Tomocerus minor there was no such difference. It is suggested that the main integumentary resistance against water loss in Orchesella cincta is the epidermal cell and in Tomocerus minor the epicuticle. The important rôle of the ventral vesicles in the water relations of Collembola was confirmed.     

Water balance in Collembola and its relation to habitat selection: Water content,haemolymph osmotic pressure and transpiration during an instar

In the two collembolan species Orchesella cincta and Tomocerus minor the water content, haemolymph osmotic pressure and transpiration rate fluctuate with the feeding rhythm during each instar. The changes in water content, however, are due to changes in dry weight, because the absolute water weight stays constant during the instar.The intake of food is probably the cause of the increase in haemolymph osmotic pressure. Increase of osmotically active substances in the blood and/or blood volume reduction may be responsible for the rise in osmotic pressure. This change in osmotic pressure in turn may affect the responsiveness of the animals to water as well as their feeding behaviour.Changes in the epicuticle and in epidermal cell membranes may cause changes in the rate of transpiration. The high rate observed during ecdysis and during the mid-instar may explain the behaviour of the animals in varied water conditions.Dehydration during the instar causes an equivalent rise in osmotic pressure for both Tomocerus minor and Orchesella cincta. The water loss appears to involve the haemolymph. The physiological state of the animal does not influence the rise in osmotic pressure. There are no signs of any osmoregulation in the two species.     

Interspecific and intraspecific selection by the predator Notiophilus biguttatus F. (Carabidae) concerning two collembolan prey species

Summary Observations on predation by the diurnally active predator Notiophilus biguttatus F., show that locomotory activity of the prey favours capture. Of the two prey species studied, Orchesella cincta and Tomocerus minor, the former is by far the most active one during the day. Since the moulting rhythm causes only part of a group of O. cincta to be active, predation towards this species is selective: active specimens are preferred. Tomocerus minor is almost inactive during the day (but may be activated by disturbance from the predator), which inhibits such a selection. Orchesella cincta also shows, when attacked, a greater escape ability than T. minor. So, inactive O. cincta are captured less easily than T. minor. Thus, locomotory activity and escape ability both cause a variable preference of the predator. When a sufficiently high number of active O. cincta specimens is present, this species will be preferred; when the number of active O. cincta specimens is low, e.g. as a consequence of predation, T. minor might be preferred.     

Pitfall-trapping as a method for studying surface dwelling collembola

Summary Pitfall-traps are used to study the phenology and activity phenomena of four surface dwelling Collembola e. g. Entomobrya nivalis (Linné), Lepidocyrtus cyaneus Tullberg, Orchesella cincta (Linné) and Tomocerus minor (Lubbock).It is concluded that Entomobrya is active during the day, whereas Orchesella and Tomocerus are active during the night. As to Lepidocyrtus no definite conclusion can be drawn.A digging-in effect is demonstrated for Tomocerus minor. A negative effect of the roofs appears during the day for Entomobrya nivalis and Lepidocyrtus cyaneus.Weather conditions exert an influence upon these surface dwelling Collembola.

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Zusammenfassung Die Fallenfangmethode wurde angewandt zum Studium der Phänologie und der Aktivität von vier Collembolen-Arten der Bodenoberfläche, nämlich Entomobrya nivalis (Linné), Lepidocyrtus cyaneus Tullberg, Orchesella cincta (Linné) und Tomocerus minor (Lubbock). Entomobrya erwies sich als tagaktive Art, Orchesella und Tomocerus sind nachtaktive Tiere. Für Lepidocyrtus waren die Resultate nicht eindeutig.Eine Reaktion auf das Eingraben der Fallen wurde festgestellt für Tomocerus minor.Fallendächer haben einen negativen Effekt auf den Fang von Entomobrya nivalis und Lepidocyrtus cyaneus während des Tages.Die Aktivität dieser Collembolen der Oberfläche wird durch Witterungsverhältnisse beeinflußt.

     

Effects of food deprivation and type of prey on predation by Notiophilus biguttatus F. (Carabidae) on springtails (Collembola)

Summary With diurnally active predators like Notiophilus biquttatus F. food deprivation is involved in predation in two ways: as a consequence of food shortage (i.e., low prey density), and as a consequence of the night period. The pattern of food intake after deprivation at night has been studied with respect to two prey species and differently deprived predators. They prey species represent a locomotory active one (Orchesella cincta) and a locomotory inactive one (Tomocerus minor). It appears that the rate of predation after deprivation shows a distinct pattern, initially high and then slowing to a more or less constant value. This pattern is influenced by food deprivation and type of prey. The beetles preying on O. cincta consumed more prey than those preying on T. minor. The more deprived predators compensated for deprivation by a higher daily predation when O. cincta was the prey, but not when T. minor was. Consequences of these findings are discussed with respect to diet composition and functional response.     

Size-specific mortality patterns in two species of forest floor Collembola

Summary Forest floor populations of Orchesella cincta (L) and Tomocerus minor (Lubbock) (Collembola; Entomobryidae) have been sampled over two generations and from length frequency distributions survivorship curves were constructed for each generation. Size-specific mortality rates were computed from size-specific survivorship data. The results reveal an asymmetrically U-shaped mortality pattern, with disproportionally high juvenile mortality. The pattern changes from one generation to the next, in particular the post-hatching mortality. Evidence from behavioural ecological research on a Collembola-specialized ground beetle is cited in favour of the hypothesis that size-specific mortality patterns are moulded by size-specific predation.     

Formation and ecological significance of aggregations in collembola

Summary Spatial distribution in the two collembolan species Tomocerus minor and Orchesella cincta is greatly influenced by the distribution of the environmental factors water and food. T. minor is totally restricted in distribution to water-saturated places, where it forms spaced-out aggregations. O. cincta assembles in water-saturated places during ecdysis and subsequent reproduction. This leads to dense contact-aggregations. Dispersal follows during the feeding period, probably caused by food shortage, presence of other species and/or saturated conditions in the aggregation site. After feeding, orientation toward water-saturated places occurs by means of orthokinetic reactions and the aggregations are reestablished. The effect of this periodical aggregation for the population is discussed.     

A comparative study of winter survival in two temperate Collembola

ABSTRACT.

• 1 We studied winter survival of two temperate collembolan species, Orchesella cincta (L.) and Tomocerus minor (Lubbock), that overwinter in adult and juvenile life stages.
• 2 A significant seasonal variation in cold hardiness, measured as lethal temperature after 24 h exposure, was found for both species. There was no difference between juveniles and adults in cold hardiness. O.cincta was more cold tolerant than T.minor.
• 3 A group of high and a group of low values for lethal temperatures could be distinguished.
• 4 Frost periods induced gut evacuation in O.cincta, but not in T.minor.
• 5 During frost periods no extra winter mortality was found in T.minor. This species moved down the soil profile as a response to a frost period without snow cover.
• 6 The winter mortality of O.cincta was difficult to estimate, since part of the population remained above ground in trees and escaped from sampling. The smallest size classes, which are restricted to the litter, had a lower winter mortality than T.minor.

     

Rhinanthus minor population genetic structure and subspecies: Potential seed sources of a keystone species in grassland restoration projects

In the last few decades unimproved semi-natural grasslands have been affected by intensification of land use and habitat fragmentation. Because of their biodiversity these species-rich grasslands are of high conservation importance and efforts are under way to restore such habitats. Detailed knowledge of within species diversity will aid deciding on the optimal seed source for such restoration projects, e.g. local genotypes or ecotypes. Rhinanthus minor is a species that is typically found in semi-natural grasslands and is commonly used in grassland restoration projects. This is because R. minor is a hemiparasitic plant that takes minerals and nutrients from its host, which in turn decreases the host's biomass and leads to opportunities for less competitive species in the vegetation. Here, we investigate genetic diversity within and between R. minor populations. This allowed us to test whether the six different subspecies of R. minor that have been described in the UK, based on their morphology, flowering time, and habitat, can be differentiated using molecular markers. We identified moderate levels of genetic differentiation between R. minor populations within the UK. In addition, R. minor individuals from the UK appear to be distinct from R. minor and Rhinanthus angustifolius individuals from other European countries based on microsatellite genotyping and DNA sequencing of cpDNA and rDNA ITS. The molecular markers used in the current study did not separate populations of R. minor based on either their subspecies or habitat. The implication for the use of R. minor in grassland restoration projects seems to be that it is not necessary to use local seeds or seeds from the same subspecies.     

Identification of the Aggregation Pheromone of the Melon Thrips,Thrips palmi

The objective of this study was to identify the aggregation pheromone of the melon thrips Thrips palmi, a major pest of vegetable and ornamental plants around the world. The species causes damage both through feeding activities and as a vector of tospoviruses, and is a threat to world trade and European horticulture. Improved methods of detecting and controlling this species are needed and the identification of an aggregation pheromone will contribute to this requirement. Bioassays with a Y-tube olfactometer showed that virgin female T. palmi were attracted to the odour of live males, but not to that of live females, and that mixed-age adults of both sexes were attracted to the odour of live males, indicating the presence of a male-produced aggregation pheromone. Examination of the headspace volatiles of adult male T. palmi revealed only one compound that was not found in adult females. It was identified by comparison of its mass spectrum and chromatographic details with those of similar compounds. This compound had a structure like that of the previously identified male-produced aggregation pheromone of the western flower thrips Frankliniella occidentalis. The compound was synthesised and tested in eggplant crops infested with T. palmi in Japan. Significantly greater numbers of both males and females were attracted to traps baited with the putative aggregation pheromone compared to unbaited traps. The aggregation pheromone of T. palmi is thus identified as (R)-lavandulyl 3-methyl-3-butenoate by spectroscopic, chromatographic and behavioural analysis.     

A peculiar cave species of Tomocerus (Collembola,Tomoceridae, Tomocerinae) from Vietnam,with a discussion of the postantennal organ and prelabral chaetae in Tomocerinae

The first Tomocerus species with a postantennal organ (PAO) in the adult stage is described from Vietnam. Tomocerus postantennalis sp. n. differs from the other PAO-possessing tomocerid, Tomolonus reductus Mills, 1948, mainly in the morphology of PAO, the number of ocelli, the number of chaetae in trochantero-femoral organ and several features of the furca. The new species is placed in Tomocerus because of the presence of a toothlet on the outer basal mucronal tooth and the absence of the diagnostic character states of Plutomurus Yosii, 1956 and Aphaenomurus Yosii, 1956. Besides the presence of PAO, the new species is peculiar in having six prelabral chaetae, instead of four as in other Tomocerus species. The new species is similar to Tomocerus folsomi Denis, 1929 and Tomocerus ocreatus Denis, 1948 in the type of dental spines but different from them in the body colour, the relative length of antennae to body, the number of unguis inner teeth and the number of mucronal intermediate teeth.     

Pheromone production in bark beetles

The first aggregation pheromone components from bark beetles were identified in 1966 as a mixture of ipsdienol, ipsenol and verbenol. Since then, a number of additional components have been identified as both aggregation and anti-aggregation pheromones, with many of them being monoterpenoids or derived from monoterpenoids. The structural similarity between the major pheromone components of bark beetles and the monoterpenes found in the host trees, along with the association of monoterpenoid production with plant tissue, led to the paradigm that most if not all bark beetle pheromone components were derived from host tree precursors, often with a simple hydroxylation producing the pheromone. In the 1990s there was a paradigm shift as evidence for de novo biosynthesis of pheromone components began to accumulate, and it is now recognized that most bark beetle monoterpenoid aggregation pheromone components are biosynthesized de novo. The bark beetle aggregation pheromones are released from the frass, which is consistent with the isoprenoid aggregation pheromones, including ipsdienol, ipsenol and frontalin, being produced in midgut tissue. It appears that exo-brevocomin is produced de novo in fat body tissue, and that verbenol, verbenone and verbenene are produced from dietary α-pinene in fat body tissue. Combined biochemical, molecular and functional genomics studies in Ips pini yielded the discovery and characterization of the enzymes that convert mevalonate pathway intermediates to pheromone components, including a novel bifunctional geranyl diphosphate synthase/myrcene synthase, a cytochrome P450 that hydroxylates myrcene to ipsdienol, and an oxidoreductase that interconverts ipsdienol and ipsdienone to achieve the appropriate stereochemistry of ipsdienol for pheromonal activity. Furthermore, the regulation of these genes and their corresponding enzymes proved complex and diverse in different species. Mevalonate pathway genes in pheromone producing male I. pini have much higher basal levels than in females, and feeding induces their expression. In I. duplicatus and I. pini, juvenile hormone III (JH III) induces pheromone production in the absence of feeding, whereas in I. paraconfusus and I. confusus, topically applied JH III does not induce pheromone production. In all four species, feeding induces pheromone production. While many of the details of pheromone production, including the site of synthesis, pathways and knowledge of the enzymes involved are known for Ips, less is known about pheromone production in Dendroctonus. Functional genomics studies are under way in D. ponderosae, which should rapidly increase our understanding of pheromone production in this genus. This chapter presents a historical development of what is known about pheromone production in bark beetles, emphasizes the genomic and post-genomic work in I. pini and points out areas where research is needed to obtain a more complete understanding of pheromone production.     

Physiological absorption of liquid water by Collembola: Absorption by the ventral tube at different salinities

The ability to absorb solutions has been examined in the coxal vesicles of the ventral tube in two sympatric surface dwelling Collembola (Tomocerus sp. and Orchesella villosa) from a beech forest. The net influx of distilled water and different sodium chloride solutions was measured, followed by examination of the effective surface of the vesicles which contacts the medium. The transport rate decreased with increasing salinity of the medium. Orchesella always showed higher absorption rates than Tomocerus, if the values were related to unit surface area. However, considering that the effective surface area of the vesicles of Tomocerus is larger, the total absorption rate by the ventral tube of Tomocerus exceeded that of Orchesella. Calculating the increase in the total water content. Orchesella compensated for its deficit faster than Tomocerus, because Orchesella is smaller in total weight and water content. In most cases the efficiency of the absorptive epithelium decreased during an absorption cycle; this also occurred before moulting. Some hours after moulting, the absorption rates increased to their former level. Comparing the rates of transpiration, absorption by the ventral-tube vesicles, and drinking, confirmed the dominant role of the ventral tube in the water balance of Collembola. It is an important factor in the strategy of adaptation from the hypogaic to the epigaic life.     

Le grégarisme chez Blaberus craniifer: Isolement et identification de la phéromone

In the gregarious cockroach, Blaberus craniifer, an aggregation pheromone is produced by all individuals (larvae and adults) except at ecdysis. The pheromone, secreted by the mandibular glands, was analysed by thin-layer and gas chromatography and by mass spectrometry. The mandibular glands secrete three major volatile products: undecane, tetradecane, and ethyl-caproate. The last component is of unknown significance, but a mixture of undecane and tetradecane ($\text{1}\text{1}$) reproduces all the effects of the natural pheromone. The distance of perception is short: 40 cm for the adults and old larvae and 10 cm for the first instar larvae. The threshold is about 0·2 ng for the adults and 0·4 ng for the first instar larvae. The mixture undecane and tetradecane is specific: it is not attractive for other gregarious cockroaches (many of which are devoid of mandibular glands), and other straight-chain saturated hydrocarbons are not attractive for B. craniifer.     

Interactions of the Hemiparasitic Species Rhinanthus minor with its Host Plant Community at Two Nutrient Levels

For root hemiparasites, host plants are both the source of water and nutrients below-ground, but competitors for light above-ground. Hemiparasites can reduce host biomass, and in this way considerably affect the whole plant community. To investigate these effects, we carried out two experiments in an oligotrophic meadow with a native population of Rhinanthus minor. In the first experiment, removal of R. minor was combined with fertilization in a factorial design, and in the second one, we manipulated R. minor density by thinning. The presence of R. minor decreased the biomass of its host community, mostly by suppressing grasses. In this way, the species was able to counterbalance the effect of fertilization, which increased community biomass and in particular that of grasses. Neither the presence of R. minor nor fertilization affected the total number of species or the Shannon-Wiener diversity index (H’) of the host community. However, H’ of grasses was higher and H’ of forbs (non-leguminous dicots) was lower in the presence of R. minor. Reduction of grasses by R. minor favored mainly the dominant forb Plantago lanceolata, which partly acquired the role of a competitive dominant. Effects of R. minor on community diversity seem to be highly dependent on the relative sensitivities of dominant and subordinate species. Fertilization increased the mortality of seedlings, resulting in a lower number of flowering plants. However, surviving individuals on average produced more flowers. Thinning resulted in lower mortality of R. minor plants. This indicates that intraspecific competition in R. minor populations results in negative density dependence.     

Analysis of orientation behaviour of Tribolium castaneum and T. confusum to synthetic aggregation pheromone

Adult male T. castaneum (Herbst) and T. confusum (du Val) secretes an aggregation pheromone that is attractive to both sexes. Orientation behaviour of the two Tribolium species responding to different concentrations of synthetic aggregation pheromone in still and moving air was studied in an 2.5 m×0.4 m olfactometer. Analysis of Tribolium tracks indicated that the aggregation pheromone stimulated the beetles to walk faster at higher concentrations to increase the frequency and magnitude of turning and to decrease track reversal distances and distances between turns. The mean walking speed of both species was lowest at the highest air speed. The behavioural responses of the beetles to the pheromone in still and moving air were similar, indicating chemotaxis as the major orientation mechanism used by both species to locate an odour source. The beetles showed greater orientation efficiency within a discrete pheromone plume than a diffuse plume.     

The role of the hemiparasitic annual Rhinanthus minor in determining grassland community structure

Summary Rhinanthus minor (yellow-rattle) is a widespread hemiparasitic plant of grassland habitats throughout Great Britain. It is usually considered to be indicative of species-rich grassland, but in a survey of 14 habitats throughout Britain it was found that R. minor at the time of flowering normally occupied relatively low-diversity patches within areas of high diversity as determined by the number of species, Simpson's Index and the Shannon-Wiener Index. Following the death of adult plants of R. minor in the summer it was shown that the pattern of species diversity changed such that by the time R. minor germinated in the following spring the differences between the areas containing and not containing R. minor were much less distinct. A perturbation experiment in which R. minor was removed from four sites indicated that the effect of the removal of R. minor on the development of community structure over the next year was to increase species diversity on three of the sites and decrease it on the fourth. Those species which responded to the removal of R. minor by an increase in abundance were shown to be preferred hosts. All three lines of evidence point to the fact R. minor has a significant effect on the species diversity of the communities in which it grows by selectively parasitizing components of the flora and modifying the competitive relationships between plants. However, as the communities generally responded to the removal of R. minor by an increase in diversity and as the general survey indicated that R. minor is generally associated with areas of low diversity it would appear that the plants which are selectively parasitized are generally not the competitive dominants in the community.     

Relationship between saturation deficit and the survival and locomotory activity of surface dwelling Collembola

The springtails Tomocerus minor, Orchesella cincta and Isotoma viridis survive only in air with a saturation deficit near zero. Their survival time is inversely related to saturation deficit and not simply to the relative humidity. The different species show different reactions to the same saturation deficit values, which agree with the humidity preferences of the species in their natural habitats.Drought stimulates Collembola to start locomotory activity which may lead them to aggregate in optimal humidity conditions. Thus this reaction may play a part in increasing the survival rate of these animals.

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Zusammenfassung Die Beziehung zwischen Sättigungsdefizit (S.D.) und Überlebenszeit und zwischen S.D. und lokomotorischer Aktivität wurde an drei epedaphischen Collembolen-Arten untersucht. Die Überlebensdauer verhält sich umgekehrt proportional zum S.D., und steht in keinem direkten Verhältnis zur relativen Luftfeuchte. Die verschiedenen Arten weisen unterschiedliche Reaktionen zu den gleichen S.D.-Werten auf. Diese Reaktionen stimmen mit den Feuchte-Präferenzen der drei Arten in ihren natürlichen Habitats überein. Hohe S.D.-Werte führen zu lokomotorischer Aktivität, mittels welcher die Tiere optimale Feuchtigkeitsverhältnisse erreichen können.Diese Ergebnisse weisen auf einen ökologischen Überlebensmechanismus hin.

     

Questions of molecular evolution of pheromone communication in caddisflies and lower moths (Insecta: Trichoptera,Lepidoptera)

Recent GS-MS and GC-EAD studies of pheromone production and perception in caddisflies and lower moths have shown that these insects use a rather limited selection of volatiles as attractants. Most of them are alcohols and ketones, although the diversity of chemicals produced by sternal glands of abdominal segment V is much wider, especially in the lower Trichoptera. Sternal pheromone glands produce only short-chain polymers in all Amphiesmenoptera. These glands are part of the ground-plan for the related orders, Trichoptera and Lepidoptera, occurring in both sexes and producing similar but not identical sets of components in males and females. The presence of pheromone volatiles is shown to be restricted to the gland segments (Fig. 1), although some other shortchain polymers do occur in the head of females of Molanna angustata (Molannidae). The pheromone blends of lower Trichoptera (Glossosomatidae, Rhyacophilidae, and Philopotamidae) are multi-component and resemble plant volatiles in composition. A hypothesis of the origin of pheromone communication is proposed postulating basic resemblance of early pheromones and plant volatiles in variety and chemical composition. These pheromones were detected by non-specialized receptors of the amphiesmenopteran ancestor and served as guides for insect aggregation on plants as well as on shores of reservoirs, marking the places suitable for a wide variety of species. The primary aggregation function of pheromones was changed in more advanced communication systems to the species-specific signaling with sex-related asymmetry of signals, although the aggregation significance persisted in some species. Pheromone communication has disappeared in some most advanced lineages (e.g., Leptoceridae) with parallel reduction of glands, secretion, and antennal receptors. The pheromone composition does not show gradual divergent evolution in related species; instead, abrupt transformation of pheromone blends with persistence of major components in remote families seems to be the typical case.     

The aggregation-attachment pheromone of the tropical bont tick Amblyomma variegatum Fabricius (Acari,Ixodidae): Isolation,identification and action of its components

Combining a new in vitro bioassay with the analytical method capillary gas chromatography-mass spectrometry, the aggregation-attachment pheromone produced by fed males of the tropical bont tick Amblyomma variegatum was shown to consist of o-nitrophenol, methyl salicylate and pelargonic acid in the approximate amounts of 2/1/8 × 10^?6 g/tick. A synthetic pheromone blend composed of those three volatile compounds evoked an aggregation response in unfed males and females in a bioassay comparable to the response to a natural pheromone source. Of the individual components. only o-nitrophenol induced a significant, although not complete aggregation response. Methyl salicylate and pelargonic acid contribute to complete pheromone activity, but induce no aggregation response at all, when offered separately.