Parasitism of the common earwigForficula auricularia [Dermaptera: Forficulidae] by tachinid flies in an apple orchard

Earwigs (Forficula auricularia L.) were collected from an untreated apple orchard every 2 weeks from June to October 1979. Percentage parasitism at the times of collection was calculated from the numbers of parasitoids that emerged. Two tachinidsRhacodineura pallipes Fallen andDigonochaeta spinipennis Meigen parasitised earwigs, starting between 21 June and 5 July and continuing through July. Parasitism byR. pallipes reached a peak of 16 % in late July; fewer earwigs were parasitised byD. spinipennis. Both tachinids had one generation per year;D. spinipennis overwintered as puparia, andR. pallipes as larvae in earwig hosts or as adults. In the orchard, puparia of both tachinid species were hyperparasitised byDibrachys cavus (Walker) (Pteromalidae) andPhygadeuon vexator (Thunberg) (Ichneumonidae).     

Host selection and larval interactions among three primary parasitoids ofPlathypena scabra (Lep.: noctuidae)

Three hymenopteran parasitoids that attackPlathypena scabra (F.) larvae often oviposit into consecutive instars of the host. We investigated host discrimination by adults and competitive interactions among larvae of these three parasitoid species. Avoidance of superparasitism byCotesia marginiventris (Cresson) andDiolcogaster facetosa Ashmead was tested. Females of each species were presented either withP. scabra parasitized by a different female of the same species 6 h earlier or unparasitizedP. scabra. Under these conditions,C. marginiventris attacked similar numbers of parasitized and unparasitized hosts.D. facetosa attacked 31% fewer parasitized than unparasitizedP. scabra. The avoidance of multiple parasitism byD. facetosa was studied in a similar bioassay. AlthoughD. facetosa females parasitized fewerP. scabra that had been attacked byC. marginiventris 6 h previously, the reduction in parasitism was only about 23%. In competition studies, immatureD. facetosa were better competitors than immatureC. marginiventris. Aleiodes (=Rogas) nolophanae (Ashmead) was an inferior competitor against bothC. marginiventris andD. facetosa when the duration between parasitism events was 1 h, but their competitive ability increased when they multiply parasitized hosts at least 32 h after the initial oviposition.     

Response patterns of net photosynthesis to moisture of mosses in xeric habitats

The response patterns of net photosynthesis to moisture level of mosses in xeric habitats were compared with those in mesic habitats, in order to determine whether the former species are better adapted to the xeric condition with regard to carbon gain. Moss species examined wereRhacomitrium lanuginosum andR. barbuloides in xeric open habitats andDicranum japonicum, Hypnum plicatulum, Ptilium crista-castrensis, Pleurozium schreberi andHylocomium splendens in mesic habitats on the coniferous forest floor in the upper subalpine zone of Mt. Fuji. Three additional xerophytic species collected at other localities,Ptychomitrium polyphylloides, Grimmia pilifera andHedwigia ciliata, were also examined. Five species in the xeric habitats showed an optimum range of moisture level for net photosynthesis, 2 to 3g·g⁻¹. On the other hand, species in the forest showed a wider optimum range, 3 to 8g·g⁻¹. Net photosynthetic rate at the moisture level of 0.5g·g⁻¹ was positive in xerophytic mosses, but negative in most forest mosses. Moisture levels where external capillary water disappeared and drop of water potential began was determined by blotting water-saturated shoots with membrane filters. These moisture levels were low in the xerophytic mosses and high in the forest mosses, although there were some exceptions. It was concluded that mosses in xeric habitats are better adapted for the efficient use of water for photosynthesis than those in mesic habitats.     

Differences in visual signal design and detectability between allopatric populations of anolis lizards

We tested the prediction of the sensory drive hypothesis using four allopatric populations of the lizard Anolis cristatellus from two distinct environments (i.e., mesic and xeric conditions). For each population, we measured habitat light characteristics and quantified signal design by measuring the spectral and total reflectance and transmittance of the dewlap. We used these data to calculate dewlap detectability using an empirically based model of signal detection probability. We found that populations from mesic and xeric conditions occupy two distinct habitats with respect to light intensity and spectral quality and that dewlap design has diverged between populations in a way that increases signal detectability in each habitat. The major difference in dewlap design was in total reflectance and transmittance, making dewlaps from xeric habitats darker and dewlaps from mesic habitats brighter. Furthermore, dewlap detection decreased significantly when a dewlap from a xeric habitat is detected under the spectral conditions of a mesic habitat. The converse is true for a dewlap from a mesic habitat. We propose that sensory drive has promoted divergence in dewlap design in distinct habitat light conditions, and we discuss the possibility that selection might promote early stages of reproductive isolation as a by-product of selection on dewlap design to distinct habitat light conditions.     

Tests of the contribution of acclimation to geographic variation in water loss rates of the West Indian lizard <Emphasis Type="Italic">Anolis cristatellus</Emphasis>

Phenotypic plasticity can contribute to the process of adaptive radiation by facilitating population persistence in novel environments. West Indian Anolis lizards provide a classic example of an adaptive radiation, in which divergence has occurred along two primary ecological axes: structural microhabitat and climate. Adaptive plasticity in limb morphology is hypothesized to have facilitated divergence along the structural niche axis in Anolis, but very little work has explored plasticity in physiological traits. Here, we experimentally ask whether Puerto Rican Anolis cristatellus from mesic and xeric habitats differ in desiccation rates, and whether these lizards exhibit an acclimation response to changes in relative humidity. We first present microclimatic data collected at lizard perch sites that demonstrate that abiotic conditions experienced by lizards differ between mesic and xeric habitat types. In Experiment 1, we measured desiccation rates of lizards from both habitats maintained under identical laboratory conditions. This experiment demonstrated that desiccation rates differ between populations; xeric lizards lose water more slowly than mesic lizards. In Experiment 2, lizards from each habitat were either maintained under the conditions of Experiment 1, or under extremely low relative humidity. Desiccation rates did not differ between lizards from the same habitat maintained under different treatments and xeric lizards maintained lower desiccation rates than mesic lizards within each treatment. Our results demonstrate that A. cristatellus does not exhibit an acclimation response to abrupt changes of hydric conditions, and suggest that tropical Anolis lizards might be unable to exhibit physiological plasticity in desiccation rates in response to varying climatic conditions.     

Host behaviour and its influence on foraging and acceptance by the solitary parasitoid wasp,Venturia canescens (Hym: Ichneumonidae)

Behavioural interactions between the solitary koinobiont parasitoid,Venturia canescens, and two of its hosts,Plodia interpunctella andCorcyra cephalonica, were investigated. The response of both hosts to simulated antennation using a two-haired brush was examined over instars 3 (L3) to 5 (L5). YoungP. interpunctella larvae predominantly adopted escape tactics (writhe, trash) whereas L5P. interpunctella usually froze after the stimulus was applied. L3C. cephalonica larvae were more aggressive (headrear, flick) thanP. interpunctella in response to the application of the stimulus, but olderC. cephalonica responded less aggressively than in earlier instars. AlthoughV. canescens readily jabbed its ovipositor at both hosts after antennation,P. interpunctella was considerably more susceptible to parasitoid attack thanC. cephalonica, irrespective of size in the final (L5) instar.C. cephalonica, the larger, more aggressive host, actively resisted parasitism whereasP. interpunctella responded much more passively after parasitoid contact. Parasitoids examined and jabbed their ovipositors at dead hosts, but this behaviour was not sustained, implying that host movement stimulates parasitoid attack. On patches containingV. canescens, L5C. cephalonica andP. interpunctella, mostP. interpunctella larvae responded by freezing after parasitoid contact.P. interpunctella that froze usually avoided parasitism, whereas larvae that attempted to escape by crawling were pursued with vigour byV. canescens and usually parasitized. Irrespective of behaviour after parasitoid contact,C. cephalonia displayed more aggressive behaviour and had much greater success in warding off parasitoid attack. Host acceptance byV. canescens is clearly affected by the size and species of the host it attacks. The influence of host defensive behaviour is discussed in relation to the evolution of parasitoid counter-defences and oviposition strategies.     

The adaptive significance of insect gall distribution: survivorship of species in xeric and mesic habitats

Summary We studied the relationship between habitat moisture and gall-forming insect populations. Population sizes for most galling taxa were significantly larger in xeric habitats compared with mesic habitats. Our results indicate that the differential abundance of galling insects in these habitats is due primarily to differential mortality and survivorship. Mortality factors acting upon eight insect galling species (belonging to eight genera and four families) were measured on six species (five genera and five families) of host plants. Survival was significantly higher for galling populations inhabiting xeric habitats compared with mesic habitats. Parasitism was higher in mesic habitats in seven of eight habitats and fungus-induced diseases were higher in five of seven habitats. Mortality due to predation and other (unknown) factors showed no clear trends. Overall, there was a tendency towards lower mortality and consequently higher survival for populations inhabiting xeric habitats. We hypothesize that reduced mortality caused by natural enemies and endophytic fungi has contributed to the speciation and radiation of galling insects in apparently harsh environments.     

Relationships of herbivore feeding and plant flavonoids (Coleoptera: Chrysomelidae and Anacardiaceae: Rhus)

Summary Eighteen leaf flavonoid compounds were isolated from several populations of Rhus tripartita from xeric habitats in Israel, ornamental Schinus terebinthifolius from Israel, and three species of Rhus (vulgaris, natalensis, tenuinervis) from mesic habitats in Kenya. Foodplant preference testing of Rhus-feeding Leaf Beetles (Blepharida sacra from Israel and B. marginalis and B. conradsi from Kenya) correlated well with the flavonoid composition of the different foodplants. Blepharida sacra and B. marginalis foodplant preferences demonstrated an herbivore sibling relationship but there is evidence, including foodplant ecology and distribution, that they are separate species. The herbivorefoodplant coevolution of the xeric B. sacra-R. tripartita is distinct from that of the mesic B. marginalis-R. vulgaris/natalensis, however, this study also indicates possible ancestral relationships between the herbivore species as well as between the plant species.     

Influence of crucifer cropping system on the parasitism ofPlutella xylostella (Lep., Yponomeutidae) byCotesia plutellae (Hym., Braconidae) andDiadegma semiclausum (Hym., Ichneumonidae)

Field experiments were conducted to study the influence of cabbage monoculture and mixed cropping on the parasitism of diamondback moth,Plutella xylostella (L.), a destructive pest of all crucifers, by 2 larval parasites,Diadegma semiclausum Hellén andCotesia plutellae Kurdjumov. There was no significant difference in parasitism by either species whether cabbage was planted in insecticide-free monoculture or in mixed cropping with 8 noncrucifers which were sprayed twice a week with chemical insecticides mevinphos, methamidophos and permethrin. Population ofP. xylostella increased as the cabbage plants grew older. Parasitism byC. plutellae was higher soon after cabbage transplanting but decreased as the plants grew older. Parasitism byD. semiclausum was very low soon after cabbage planting but increased as the plants grew older. A significant negative correlation was found betwen parasitism byC. plutellae andD. semiclausum. In a caged field study where only one parasite species was used in an individual cage, parasitism ofP. xylostella by both species decreased as theP. xylostella population increased. This is believed to be due to the absence of competition between the two parasites inside the cage. There was no relationship between host-plant age and parasitism ofP. xylostella larvae by either parasite species.     

Metabolic rate,thermoregulation and water balance in Lagidium viscacia inhabiting the arid Andean plateau

Lagidium viscacia inhabits where water and food availability is low. We hypothesize that this rodent should minimize metabolic rate and water loss in order to cope with such extreme environments. We observed that Lagidium viscacia has (1) a comparatively lower basal metabolic rate (67%) and thermal conductance (78%) of predicted; (2) a higher pulmocutaneous evaporation rate which is 36% (mesic) and 63% (xeric); and (3) energetic cost of maintaining the water balance similar to that expected for rodents from xeric environments (2.8 cal/g h). In summary, Lagidium viscacia has physiological traits that favour energy and water economy to cope with such extreme habitats.     

Phenotypic plasticity of desiccation resistance in Glossina puparia: are there ecotype constraints on acclimation responses?

Phenotypic plasticity allows organisms to cope with environmental variation and may aid in the evolution of novel traits. However, whether phenotypic plasticity is beneficial, or if acclimation responses might be constrained to particular ecotypes is generally poorly explored. Here we test the beneficial acclimation hypothesis (BAH) and its alternatives for desiccation resistance to atmospheric moisture in mesic‐ and xeric‐adapted Glossina species. Highly significant interactions among acclimation and test humidity were detected for water loss rates indicative of significant phenotypic plasticity. Ordered‐factor anova was unable to reject predictions of the ‘drier is better’ acclimation hypothesis in xeric Glossina morsitans and mesic G. austeni. Evidence for the ‘deleterious acclimation hypothesis’ was found for mesic G. palpalis as expected from the moist habitats it typically occupies. By contrast, support for the ‘optimal acclimation hypothesis’ was found in xeric G. pallidipes. Little support for BAH was obtained in the present study, although other hypotheses, which might enhance fitness within the environments these species are typically exposed to, were supported. However, acclimation responses were not necessarily constrained to xeric/mesic ecotypes which might be expected if adaptation to a particular environment arose as a trade‐off between plastic responses and living in a particular habitat. These results highlight the complexity of acclimation responses and suggest an important role for phenotypic plasticity in moderating environmental effects on evolutionary fitness in Glossina.     

Landscape patterns of litter decomposition in alpine tundra

A two-year study of the decomposition of alpine avens (Acomastylis rossii) foliage in alpine tundra of the Front Range of Colorado demonstrated a strong landscape-mediated effect on decay rates. Litter on sites with intermediate amounts of snowpack decayed more rapidly than litter on sites with larger or smaller amounts of snow. Annual decay constants (k-values) of this foliage ranged from-0.33 in dry tundra to-0.52 in moist tundra to-0.47 in the wettest habitat. No site differences in mass loss of litter were detected until late winter-early spring of the first year of decomposition, when significantly faster decomposition was observed for litter beneath the snowpack. In spite of obvious landscape-related patterns in rates of litter decomposition, total microarthropod densities in the top 5 cm of soil did not differ among habitats. However, the relative abundance of the oribatid and prostigmatid mites did vary significantly across the landscape in relation to the moisture gradient. Oribatid mites comprised a greater proportion of total mites in wetter areas. Microarthropod densities and composition, as well as patterns of decomposition, were compared with previous alpine, as well as arctic tundra, studies. The effects of soil invertebrates on decomposition rates in the alpine were evaluated with a mushroom litterbag decomposition experiment. Naphthalene was used to exclude fauna from a subset of litterbags placed in mesic and xeric habitats. Mushrooms without naphthalene additions decayed significantly faster in the mesic sites. Densities of invertebrates were also greater on mushrooms in these mesic sites. Mushrooms placed in xeric sites generally lacked fauna. Thus, both the activities and the composition of the detritus-based food web appear to change substantially across the moisture gradient found in alpine tundra.     

Structural differentiation of microhabitats of sympatricmacaca fascicularis andM. nemestrina in East Kalimantan,Indonesia

Macaca nemestrina andM. fascicularis coexist through much of their geographic ranges in Southeast Asia, but locally they segregate into drier hilly terrain and wetter alluvial riverine terrain respectively. SinceM. fascicularis travel arboraally andM. nemestrina, travel terrestrially, structural characteristics of habitats on the two different substrates may explain local segregation of these two species. This paper reports measures comparing habitat structure ofM. fascicularis fascicularis andM. nemestrina nemestrina at the Mentoko site in East Kalimantan, Indonesia. Results show that (1) ground cover is thicker; (2) there are fewer gaps in the canopy; and (3) the foliage of the canopy is more dense in habitat occupied by arborealM. f. fascicularis than in habitat occupied byM. n. nemestrina. These differences in habitat structure appear to explain segregation of the two species at the Mentoko. Similar differences in habitat may permit coexistence of the two species throughout their geographical ranges.     

Are microbial symbionts involved in the speciation of the gall-inducing aphid, <Emphasis Type="Italic">Slavum wertheimae</Emphasis>?

Microbial symbionts have come to be recognized as agents in the speciation of their eukaryote hosts. In this study, we asked if bacterial symbionts are, or were in the past, involved in the speciation of the gall-inducing aphid Slavum wertheimae (Hemiptera: Aphididae). This aphid is specific to the tree Pistacia atlantica, which has a fragmented distribution among mesic and xeric habitats, leading to corresponding fragmentation of the aphid population. Previous studies revealed genetic differentiation among populations of the gall-inducing aphid, suggesting cryptic allopatric speciation. Pistacia atlantica trees show no such variation. By means of diagnostic PCR, we screened several populations of S. wertheimae from mesic and xeric sites in Israel for the presence of nine known aphid symbionts: Arsenophonus, Hamiltonella, Regiella, Rickettsia, Rickettsiella, Serratia, Spiroplasma, Wolbachia, and X-type, as well as Cardinium, known to be a reproductive manipulator. Only one symbiont, Wolbachia, was detected in S. wertheimae. Wolbachia was found in all the aphids of the mesic populations, compared to 26% in the aphids from the xeric populations. Multilocus Sequence typing of Wolbachia revealed new haplotypes in the fbpA and coxA genes in both the mesic and xeric populations. Phylogenetic analysis showed that Wolbachia of S. wertheimae is closely related to Wolbachia strains from assorted hosts, mostly lepidopterans, but only distantly related to Wolbachia strains from other aphid species. We conclude that the cryptic speciation of mesic and xeric populations of S. wertheimae was likely driven by geographical isolation rather than by Wolbachia.     

扎龙湿地芦苇分株生态可塑性及其对土壤因子的响应

扎龙湿地的芦苇既可形成大面积的单优群落,也可形成不同群落斑块。采用大样本抽样调查与统计分析方法,对湿地内水生生境、湿生生境、旱生生境和盐碱生境芦苇种群分株高度和生物量进行比较。结果表明,6—10月份,4个生境芦苇种群分株高度及生物量均以水生生境最高,盐碱生境最低,水生生境株高为盐碱生境的1.5—2.3倍,分株生物量为2.0—5.1倍,生境间的差异性以及差异序位均相对稳定。4个生境株高生境间变异系数(19.45%—31.56%)均高于生境内变异系数(8.07%—17.61%),分株高度在生境间的可塑性更大;分株生物量中水生生境、湿生生境和盐碱生境3个生境间的变异系数(33.43%—55.61%)均低于生境内变异系数(44.85%—79.82%),分株生物量在生境内的可塑性更大。不同生境条件下芦苇种群分株,在生长和生产上均存在较大的生态可塑性,表现出明显的环境效应,其中土壤含水量是该地区芦苇分株生态可塑性变异的主要驱动因子(R0.80),为正向驱动。     

Stimulus selection (light) in four subspecies of deermice (Peromyscus maniculatus)

Abstract

Four subspecies of deermice (Peromyscus maniculatus) were selected from habitats along a gradient from mesic hardwood forests (gracilis), tall grass prairie (bairdi), short grass prairie (nebrascensis), to desert grassland (labecula) in effort to relate the light preferences of the mice to the habitat of their origin. Six individuals of each subspecies were maintained in dark chambers for 25 days, during which they could turn on a dim light for 30 seconds on ten of these days. Mice from the mesic habitats turned the lights on more frequently (light reinforcement) than mice from xeric habitats. The same subspecies that exhibited light reinforcement when raised in laboratory light conditions failed to show light reinforcement when raised in total darkness. The circadian periodicities also differed significantly among the subspecies. Conclusions drawn from the results were: (1) selection for light is genetically influenced as indicated by subspecific differences, (2) some genotypes are readily modified by environmental light conditions than others, and (3) natural selection in each environment appears to contribute to the degree of genetic fixation or genetic plasticity.     

Forecasting ecological and evolutionary strategies to global change: an example from habitat selection by lemmings

Ecologists and evolutionary biologists must develop theories that can predict the consequences of global warming and other impacts on Earth's biota. Theories of adaptive habitat selection are particularly promising because they link distribution and density with fitness. The evolutionarily stable strategy that emerges from adaptive habitat choice is given by the system's habitat isodar, the graph of densities in pairs of habitats such that the expectation of fitness is the same in each. We illustrate how isodars can be converted into adaptive landscapes of habitat selection that display the density‐ and frequency‐dependent fitness of competing strategies of habitat use. The adaptive landscape varies with the abundance of habitats and can thus be used to predict future adaptive distributions of individuals under competing scenarios of habitat change. Application of the theory to three species of Arctic rodents living on Herschel Island in the Beaufort Sea predicts changes in selection gradients as xeric upland increases in frequency with global warming. Selection gradients will become more shallow for brown lemming (Lemmus trimucronatus) and tundra vole (Microtus oeconomus) strategies that preferentially exploit mesic habitat. Climate change will cause selection gradients for the alternative strategy of using mostly xeric habitat to become much steeper. Meanwhile, the adaptive landscape for collared lemmings (Dicrostonyx groenlandicus), which specialize on xeric Dryas‐covered upland, will become increasingly convex. Changes in the adaptive landscapes thus predict expanding niches for Lemmus and Microtus, and a narrower niche for Dicrostonyx. The ability to draw adaptive landscapes from current patterns of distribution represents one of the few methods available to forecast the consequences of climate change on the future distribution and evolution of affected species.     

Drought alters the expression of mating system traits in two species of Clarkia

Variation in mating system traits can have important consequences for plant populations by affecting reproductive assurance, the expression of inbreeding depression, and the colonization of and persistence in new or altered habitats. Environmental stressors, such as drought, have been hypothesized to induce higher rates of self-fertilization, yet this hypothesis has rarely been tested. Here we measure the response of two sister species of self-compatible annual herbs from contrasting habitats, Clarkia breweri and C. concinna, to an experimentally imposed greenhouse drought treatment. We find that the species differ in their baseline per-flower autogamy rates and the degree of spatial and temporal separation of male and female function within their flowers. Both species show a reduction in temporal separation of anthesis and stigma receptivity with the drought treatment. However, the species from the more mesic habitat, C. concinna, increases its low autogamy rate under drought conditions, whereas the species from the more xeric habitat, C. breweri, decreases its high autogamy rate under drought conditions. Neither species showed a response to drought in flower size or anther-stigma distance. Our results demonstrate that the induction of selfing under environmental stress cannot be assumed and that, in this case, the developmental timing of flower maturation is more plastic than floral morphology.     

Aleochara suffusa andA. bilineata (Col.: Staphylinidae) as parasitoids of brassica root flies in northern Norway

A sample ofDelia puparia collected in late autumn from a brassica field at Tromsø, northern Norway, was investigated to study the level of parasitism byAleochara. BothA. suffusa andA. bilineata were reared from puparia of the cabbage root fly,Delia radicum, and the bean seed flies,D. florilega and/orD. platura. Only two specimens ofA. bilineata emerged from puparia of the turnip root fly,D. floralis. BothAleochara species hibernated in the larval state and both pupated inside the host puparium. Most specimens ofA. suffusa emerged from small hosts (D. florilega/D. platura), whereas the majority of A.bilineata emerged from host species of larger size (D. radicum/D. floralis). The time to develop from first instar larva to adult was similar for bothA. suffusa andA. bilineata. Parasitoids developing in large hosts emerged later than those in small hosts, the delay being the same for both species ofAleochara.     

Parasitism of the apple maggot,Rhagoletis pomonella,infesting hawthorns in Washington

Five species of larval parasitoids were reared fromRhagoletis pomonella (Walsh) infested fruit of hawthorn,Crataegus, collected from several locations in southwest Washington over a four year period. A braconid,Biosteres melleus (Gahan), parasitized larvae infesting fruits of a native hawthorn species,Crataegus douglasii Lindl. Another braconid,Opius downesi Gahan, emerged exclusively fromR. pomonella pupae reared from fruits of an introduced species of hawthorn,Crataegus monogyna Jacq. A pteromalid,Pteromalus sp., and two eulophids,Tetrastichus spp., attackedR. pomonella larvae infesting fruits of both hawthorn species. No parasitoids emerged from a total of 4385 pupae reared from apple. Percent parasitism ofR. pomonella was higher inC. monogyna compared toC. douglasii fruits. The highest average levels of parasitism ofR. pomonella inC. monogyna andC. douglasii fruits were 90% and 23% respectively. The kinds of parasitoids, their relative abundances and timing of parasitization on the two hawthorns was related to differences in fruit ripening patterns and its effect on the development ofR. pomonella on these two hosts. Parasitization ofR. pomonella byTetrastichus spp. is a new host record. The detection of these species andPteromalus sp. in southwest Washington are the first records of ectoparasitoids attacking this tephritid.