Release of phylogenetic constraints through low resource heterogeneity: the case of gall-inducing sawflies

Abstract. 1. A group of six unusual sawfly species, which do not conform to the phylogenetic constraints hypothesis as it has been applied to sawflies, was examined in natural populations. All species were in the genus Pontania (Hymenoptera: Tenthredinidae), which induce galls on leaves of willow species (Salicaceae). An understanding of these non‐conformist species was important as a test of the validity of the general hypothesis. 2. The six species of sawfly, Pontania mandshurica, P. cf. arcticornis, P. aestiva, P. arcticornis, P. pacifica, and P. nr. pacifica, showed no oviposition preference for long, vigorous shoots, in contrast to 37 documented tenthredinid species that have demonstrated such a preference. Rather, the non‐conformist species attacked the shortest shoot length classes more frequently and larval establishment in galls was successful. 3. The evident escape from the phylogenetic constraint, which commonly limits sawfly attack to the most vigorous shoots in a willow population, resulted from low apparent heterogeneity of the resources exploited by these Pontania species. At the time of female oviposition, shoots and leaves were too uniform to allow discrimination by females among shoot length classes, resulting in random, or near random attack of shoots. 4. The unusual relative uniformity of resources to which sawflies were exposed resulted from several characteristics. (1) Females emerged early relative to shoot growth phenology, making discrimination among shoot length and vigour difficult or impossible. (2) Low heterogeneity in leaf length resulted in resource similarity independent of shoot length. (3) Abscission of leaves occurred after emergence of larvae from leaf galls so that differential abscission of leaves in relation to shoot length became irrelevant. (4) In some cases, low variance in shoot lengths was evident in old ramets lacking long, vigorous shoots. Probably as a result of low resource heterogeneity, larvae survived well across all shoot length classes, revealing no ovipositional preference and larval performance linkage related to the exploitation of the longest shoot length classes in a population of willows, as in the conformist species. Therefore, larval survival did not provide positive feedback on female preferential behaviour for long shoots, as in the conformist species studied.     

Long-term effects of exogenous methyl jasmonate application on Scots pine (Pinus sylvestris) needle chemical defence and diprionid sawfly performance

Scots pine [ Pinus sylvestris L. (Pinaceae)] trees with four different seed origins were exposed to exogenous applications of the elicitor, methyl jasmonate (MeJA), for three consecutive years. We studied the effects of MeJA on needle chemistry (including monoterpenes, sesquiterpenes, and tricyclic resin acids), plant growth, and the performance of two diprionid sawflies, the European pine sawfly ( Neodiprion sertifer Geoffr.) and the common pine sawfly ( Diprion pini L.) (both Hymenoptera: Diprionidae). In general, foliar MeJA application affected the whole range of needle secondary chemistry with significantly higher concentrations of two monoterpenes, β-pinene and limonene, in particular. Furthermore, for some seed origins the growth rates of N. sertifer and D. pini larvae were lower on needles of MeJA-treated plants with either high total terpene or high resin acid concentrations. However, inconsistencies in diprionid sawfly performance within each studied Scots pine origin suggest genetic variance in needle secondary chemistry. The differences between selected seed origins and notably variable responses to MeJA application imply that adaptation of the seed to new conditions may have had an impact on secondary chemistry and, thus, on insect performance. Finally, our results suggest that modification of Scots pine defence by a low-concentration exogenous elicitor affects the production of terpenoids in the newly growing needles, leading to poorer pine sawfly performance in origins with high terpenoid content, while not harming the growth of Scots pine trees.     

Geographic variation in the field response of male European pine sawflies, Neodiprion sertifer, to different pheromone stereoisomers and esters

The European pine sawfly, Neodiprion sertifer (Geoffroy) (Hymenoptera: Diprionidae), is a widespread and economically important forest insect. The sex pheromone communication system of this species has been previously investigated in North America, Japan and Europe, with the acetate or propionate of the alcohol (2S,3S,7S)-3,7-dimethyl-2-pentadecanol (diprionol) shown to be the main pheromone component. In some locations, male attraction either increased or decreased by the addition of the (2S,3R,7R)-diprionyl acetate isomer. However, these studies were made with different batches of synthetic pheromones, with different types of traps and according to different procedures, so the observed differences might not reflect true geographic variation. Here we investigate the geographic pattern of male sawfly response by using identical chemicals, traps and experimental procedures at eight field sites ranging from Japan in the east to Canada in the west. We found an increased inhibitory effect of the (2S,3R,7R)-isomer from Japan and Siberia to Europe. At the eastern sites, increasing amounts of the (2S,3R,7R)-isomer up to and equal to the amount of the (2S,3S,7S )-isomer, did not influence the trap catch, whereas at sites in Europe, as little as 1% of the (2S,3R,7R)-isomer almost completely inhibited the attraction. The response of the North American population was intermediate. The only site in which the (2S,3R,7R)-isomer was essential for the attraction of males was in Siberia. A similar pattern was found for the (2S,3R,7S)-isomer. Both the acetate and the propionate form of the (2S,3S,7S)-isomer were attractive by themselves in Japan, Europe and North America, and neither the (2S,3R,7S)-isomer nor the (2S,3R,7R)-isomer alone were attractive, in the acetate or propionate form. We discuss the significance of our findings for the development of more efficient monitoring schemes and for the causes of population divergence and speciation in the European pine sawfly.     

Choosy egg parasitoids: Specificity of oviposition-induced pine volatiles exploited by an egg parasitoid of pine sawflies

Generalist parasitoids are well‐known to be able to cope with the high genotypic and phenotypic plasticity of plant volatiles by learning odours during their host encounters. In contrast, specialised parasitoids often respond innately to host‐specific cues. Previous studies have shown that females of the specialised egg parasitoid Chrysonotomyia ruforum Krausse (Hymenoptera: Eulophidae) are attracted to volatiles from Pinus sylvestris L. induced by the egg deposition of its host Diprion pini L. (Hymenoptera: Diprionidae), when they have previously experienced pine twigs with host eggs. In this study we investigated by olfactometer bioassays how specifically C. ruforum responded to oviposition‐induced plant volatiles. Furthermore, we studied whether parasitoids show an innate response to oviposition‐induced pine volatiles. Naïve parasitoids were not attracted to oviposition‐induced pine volatiles. The attractiveness of volatiles from pines carrying eggs was shown to be specific for the pine and herbivore species, respectively (species specificity). We also tested whether not only oviposition, but also larval feeding, induces attractive volatiles (developmental stage specificity). The feeding of D. pini larvae did not induce the emission of P. sylvestris volatiles attractive to the egg parasitoid. Our results show that a specialist egg parasitoid does not innately show a positive response to oviposition‐induced plant volatiles, but needs to learn them. Furthermore, the results show that C. ruforum as a specialist does not learn a wide range of volatiles as some generalists do, but instead learns only a very specific oviposition‐induced plant volatile pattern, i.e., a pattern induced by the most preferred host species laying eggs on the most preferred food plant.     

Population recovery and spatial dynamics of colony recruitment in a harvester ant: a case study in a park

The recovery process of Messor aciculatus (Fr. Smith) harvester ant colonies from habitat disturbance by construction work in an urban park was investigated from 1989 to 1994. Colonies located in 1989 were considered to be survivors of the disturbance, and colonies located for the first time after 1990 were considered to be recruits. The colonies continuously increased in number after the disturbance, and the population size more than doubled just after the disturbance. Analyses of the nest site distribution of colonies in 1989 and 1994 suggest that landform modification destroyed some of them, and that the changed nest site distribution in 1989 affected the distribution in 1994, or, in other words, the disturbance indirectly affected the nest distribution 5 years later. Analyses of the nearest neighbor to each colony suggested that established colonies would obstruct newly recruited colonies around their nests. Construction may open up space for recruitment colonization by removing established colonies, and may also create suitable conditions by destruction of original vegetation, or returning vegetation to the early stages of plant community succession. As a result, the disturbance may facilitate the subsequent recruitment of new colonies and rejuvenate the population.     

Effects of added nitrogen on leaf nitrogen concentration and population dynamics of insects associated with Rumex obtusifolius L.

A series of experiments was designed to study the effects of changes in leaf nitrogen (N) concentration on population dynamics of a range of insects associated with Rumex obtusifolius. During the study period, the N concentration in leaves fluctuated between 2 and 6% dry weight. The insects at both study sites showed a pattern of shift in time for peak population density (time‐shift). This suggests that the insect community dynamics might be closely related to the allocation and distribution of resources by the host‐plant. The elevated N concentration in the host‐plant did not change the temporal order of the peak population densities of the insects, although it may determine the time for the optimal exploitation of resources by each insect species.     

Population dynamics in changing environments: the case of an eruptive forest pest species

In recent decades we have seen rapid and co‐occurring changes in landscape structure, species distributions and even climate as consequences of human activity. Such changes affect the dynamics of the interaction between major forest pest species, such as bark beetles (Coleoptera: Curculionidae, Scolytinae), and their host trees. Normally breeding mostly in broken or severely stressed spruce; at high population densities some bark beetle species can colonise and kill healthy trees on scales ranging from single trees in a stand to multi‐annual landscape‐wide outbreaks. In Eurasia, the largest outbreaks are caused by the spruce bark beetle, Ips typographus (Linnaeus), which is common and shares a wide distribution with its main host, Norway spruce (Picea abies Karst.). A large literature is now available, from which this review aims to synthesize research relevant for the population dynamics of I. typographus and co‐occurring species under changing conditions. We find that spruce bark beetle population dynamics tend to be metastable, but that mixed‐species and age‐heterogeneous forests with good site‐matching tend to be less susceptible to large‐scale outbreaks. While large accumulations of logs should be removed and/or debarked before the next swarming period, intensive removal of all coarse dead wood may be counterproductive, as it reduces the diversity of predators that in some areas may play a role in keeping I. typographus populations below the outbreak threshold, and sanitary logging frequently causes edge effects and root damage, reducing the resistance of remaining trees. It is very hard to predict the outcome of interspecific interactions due to invading beetle species or I. typographus establishing outside its current range, as they can be of varying sign and strength and may fluctuate depending on environmental factors and population phase. Most research indicates that beetle outbreaks will increase in frequency and magnitude as temperature, wind speed and precipitation variability increases, and that mitigating forestry practices should be adopted as soon as possible considering the time lags involved.     

Population dynamics of insects associated with Rumex obtusifolius in different habitats

The effect of different habitats on insect communities associated with Rumex obtusifolius was studied in detail. Study sites were selected for their variety of environmental characteristics (vegetation and habitat): shaded woodland, disturbed wasteland and pasture. The results of this study were that insect populations associated with R. obtusifolius responded differently to the different habitats. The observed differences in population dynamics among the insects showed quite clearly their responses to different habitats. There was also a pattern of time partitioning in the exploitation of the host‐plant among the insect species observed. Philaenus spumarius at nymphal stage had a peak density on approximately 20 June, Apion frumentarium and Apion spp. (Apion species other than A. frumentarium) had a peak density on approximately 30 June and Aphis rumicis had a peak density on approximately 28 July. This pattern of shift in time for peak population density (time‐shift) among the insects sharing a common host‐plant may guarantee each insect the opportunity to exploit the plant to a maximum.     

Life history and population dynamics of the western mosquitofish: a comparison of natural and introduced populations

Life history and population dynamic patterns of Gambusia affinis in southeastern Louisiana varied spatially and temporally in 1990 and 1991, but were consistent with previous reports of this species in the southern regions of its natural range. Several differences exist among populations in different geographic regions within the United States, as reported in the literature, which do not follow a' native v . introduced' dichotomy: (1) brood size decreases and offspring size increases from north to south; (2) large overwintered females in northern areas produce more broods within a season than those in southern populations, while the reverse is true for young-of–year females; (3) minimum size at first reproduction follows a seasonal pattern within populations, but tends to be smaller in southern and larger in northern and Hawaiian populations; (4) synchronous reproduction early in the season is characteristic of northern populations, but does not occur in southern areas; and (5) mosquitofish reproduce year–round in Hawaii, while 'southern' populations within the continental U.S. cease reproduction during winter.     

平背叶蜂族一新属新种暨分属检索表(膜翅目:叶蜂科)

记述广西壮族自治区十万大山地区平背叶蜂族1新属：蔡氏叶蜂属Caiina gen．nov．及1新种：短鞘蔡氏叶蜂Caiina brevitheca Wei sp．nov．，该属隶属于叶蜂科平背叶蜂亚科平背叶蜂族歧爪叶蜂亚族，与歧爪叶蜂属Nagamasaia Togashi最近似，但唇基端部亚截形，缺口很浅，爪内齿不显著长于外齿，前翅2Rs室显著短于1R1 1RS之和，后翅具1个封闭中室，Rs室开放，后足跗节明显长于胫节，锯鞘端等长于锯鞘基，锯刃平刃型，具多数微小的亚基齿，锯腹片刺毛带互相连接等，与之显著不同。编制了平背叶蜂族分亚族和属检索表。模式标本保存于中南林学院昆虫模式标本室。     

An approach to the nonlinear dynamics of Russian wheat aphid population growth with the cusp catastrophe model

Many insect field populations, especially aphids, often exhibit irregular and even catastrophic fluctuations. The objective of the present study is to explore whether or not the population intrinsic rates of growth ( r _m) obtained under laboratory conditions can shed some light on the irregular changes of insect field populations. We propose to use the catastrophe theory, one of the earliest nonlinear dynamics theories, to answer the question. To collect the necessary data, we conducted a laboratory experiment to investigate population growth of the Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), in growth chambers. The experiment was designed as the factorial combinations of five temperatures and five host plant-growth stages (25 treatments in total): 1800 newly born RWA nymphs arranged in the 25 treatments (each treatment with 72 repetitions) were observed for their development, reproduction and survival through their entire lifetimes. After obtaining the population intrinsic rates of growth ( r _m) from the experimental data under various environmental conditions, we built a cusp catastrophe model for RWA population growth by utilizing r _m as the system state variable, and temperature and host plant-growth stage as control variables. The cusp catastrophe model suggests that RWA population growth is intrinsically catastrophic , and dramatic jumps from one state to another might occur even if the temperature and plant-growth stage change smoothly . Other basic behaviors of the cusp catastrophe model, such as catastrophic jumps , hystersis and divergence , are also expected in RWA populations. These results suggest that the answer to the previously proposed question should be "yes".     

Rainfall and host reproduction regulate population dynamics of a specialist seed predator

1. Mast seeding is a widespread resource pulse caused by synchronized and intermittent production of a large seed crop by plant populations. The effects of masting on wildlife have been well documented in granivorous vertebrates, but less is known about its impact on population dynamics of insects. 2. This study investigated, over 6 years, variation in abundance of a specialist weevil (Curculio elephas) preying on holm oak (Quercus ilex) acorns. 3. An immediate bottom-up effect of seed production on weevil larval abundance was detected, which was driven by an increase in realised fecundity and aggregation at seed-rich trees. Moreover, trees producing on average more and larger acorns sustained larger weevil populations. However, no correlation was found between current and previous year adult abundance, suggesting that C. elephas did not capitalise on the reproductive bottom-up effect. 4. It was rainfall, not masting, that most strongly shaped the temporal variation in insect abundance. Rainfall facilitates emergence after diapause at underground earth cells and was also responsible for among-tree synchronisation in adult weevil population dynamics. 5. In spite of their trophic specialisation, not only food availability, but also weather affects weevil numbers. The present results indicate that moving beyond bottom-up effects is required to better understand complex systems that involve masting plants and insects that consume their seeds.     

Varietal resistance, population dynamics and timing insecticidal application with peak oviposition by Scirpophaga incertulas (Walker) (Lepidoptera: Pyralidae) on rice

The flight activity of yellow stem borer Scirpophaga incertulas (Walker) (Lepidoptera: Pyralidae) peaked in the months of April-May, May-June, August-September and October. The number of egg masses and the number of adults attracted to light sources were the indicators of S. incertulas flight activity. The rice varieties TKM6, IR22, IR60, IR66 and IR74 were infested at 7, 10, 12 and 16 wk after planting with 5, 10, 20 and 40 neonates of S. incertulas. All varieties except IR66 were susceptible to dead heart damage by S. incertulas. When the rice varieties TKM6, BPIRi2, BPIRi4, IR22, IR36, IR60, IR66 and IR74 were treated with carbofuran insecticide at the time of peak oviposition by S. incertulas in the field, the dead heart damage on all the varieties was significantly reduced in comparison with the untreated plots. Indiscriminate routine insecticidal treatments (fixed schedule) can be replaced by a treat-when-necessary schedule based on the population dynamics of S. incertulas.     

20-Hydroxyecdysone-induced changes in the cell volume of lepidopteran cells associated with population dynamics

Summary The insect cell line MRRL-CH derived from embryos of the lepidopteranManduca sexta responded rapidly, within 15 min, to 20-hydroxyecdysone (20-OH-Ec) (1×10⁻⁸ M) by increasing in cell volume. The induction time for this response contrasts with that for the cell elongation response that appears only after 24 to 48 h. The increase in cell volume represents the most rapid 20-OH-Ec-induced change in cell morphology reported to date. It also has some steroid specificity because no volume change was induced by ecdysone (4×10⁻⁶ M) under the experimental conditions. The magnitude of the cell volume response to 20-OH-Ec varied with the population dynamics of the cell line and was associatated with cell size at the time of treatment. This is a portion of a thesis submitted by L. H. E. in partial fulfillment of the requirements for the Ph.D. degree and published with the approval of the Director of the North Dakota Experiment Station as Journal Article 1130. Mention of a proprietary product or company name in this paper does not imply endorsement by the U.S. Department of Agriculture.     

Population structure and dynamics of an evergreen shade herb, Ainsliaea apiculata (Asteraceae), with special reference to herbivore effects

The population structure and dynamics of Ainsliaea apiculata, a forest understory evergreen herb widely distributed in Japan, was examined in a Chamaecyparis obtusa forest in Ibaraki Prefecture, central Japan (36°51N, 140°33E; 750 m a.s.l.). The mean population growth rate () calculated from the transition matrices for 4 years was 0.69 per year, predicting that the population size will decrease remarkably. There was a significant positive correlation between the survival of old leaves and the growth of new shoots in the following year. The shoots, especially new leaves, were damaged severely by herbivores (caterpillars of Leioptilus sp.). The survival rate of leaves formed in the previous spring to the next spring was remarkably low (41–54%). The growth of new shoots depended mainly on the reserves contained in old shoots, especially those in old leaves. New shoots of A. apiculata began to develop in spring, even though they were formed in autumn of the previous year. A defoliation experiment also showed that the removal of old shoots at the beginning of the growing season significantly inhibited the growth of new shoots. Damage to old shoots by herbivores severely influenced the growth and population dynamics of A. apiculata.     

锦界生态工业园水资源系统动力学仿真与调控

如何合理开发利用水资源,保护区域生态环境,实现人与自然的和谐发展,是当今世界所面临的共同问题.以陕北锦界生态工业园水资源系统为例,在分析系统结构的基础上,构建了水资源系统动力学模型,确定水技术进步因子、水资源循环利用率、污水处理投资率、万元产值年耗水量、日人均用水量为调控参数,进行仿真模拟.结果表明,当水技术进步因子由1提高到1.6,水资源循环利用率由0.45提高到0.85,污水处理投资率由0.18提高到0.25,万元产值年耗水量由236.8 t·a-1降为175.4 t·a-1,日人均用水量由0.18 t·d-1降为0.12 t·d-1时,园区工业总产值增长率5年可达到44.4%,水资源存量年均增幅为0.03%,水资源供需比为2.25,系统达到相对最优状态.     

Incoherent neutron scattering of copper azurin: a comparison with molecular dynamics simulation results

The low-frequency dynamics of copper azurin has been studied at different temperatures for a dry and deuterium hydrated sample by incoherent neutron scattering and the experimental results have been compared with molecular dynamics (MD) simulations carried out in the same temperature range. Experimental Debye-Waller factors are consistent with a dynamical transition at approximately 200 K which appears partially suppressed in the dry sample. Inelastic and quasielastic scattering indicate that hydration water modulates both vibrational and diffusive motions. The low-temperature experimental dynamical structure factor of the hydrated protein shows an excess of inelastic scattering peaking at about 3 meV and whose position is slightly shifted downwards in the dry sample. Such an excess is reminiscent of the “boson peak” observed in glass-like materials. This vibrational peak is quite well reproduced by MD simulations, although at a lower energy. The experimental quasielastic scattering of the two samples at 300 K shows a two-step relaxation behaviour with similar characteristic times, while the corresponding intensities differ only by a scale factor. Also, MD simulations confirm the two-step diffusive trend, but the slow process seems to be characterized by a decay faster than the experimental one. Comparison with incoherent neutron scattering studies carried out on proteins having different structure indicates that globular proteins display common elastic, quasielastic and inelastic features, with an almost similar hydration dependence, irrespective of their secondary and tertiary structure. Received: 12 October 1998 / Revised version: 19 February 1999 / Accepted: 1 March 1999     

中国钩瓣叶蜂属一新种及一新记录种(膜翅目:叶蜂科)

记述采自山东的中国钩瓣叶蜂属Macrophya Dahlbom 1新种：斑咐钩瓣叶蜂Macrophya maculotarsalina Wei et Liu.sp.nov.与Macrophya vacillans近似,但小盾片附片黑色,后足跗节大部白色,后足胫节具红斑,腹部第2背板两侧具侧白斑,第3、4背板无白斑,背地里单眼后区宽长比大于2,侧沟明显,锯腹片的锯刃强烈突出等,易与后者鉴别,斑股钩瓣叶蜂Macrophya femorata Marlatt,1898是中国新记录种,该种原记载分布于日本,新种的模式标本保存于中南林学院昆虫模式标本室。     

Biological control: Premises,ecological input and Mimosa pigra in the wetlands of Australia's Top End

The adverse impacts of weeds on natural ecosystems, together with the inadequate outcomes from treating weeds as a symptom, have escalated interest in finding efficacious control methods. With the aim of protecting wetlands from invasive weeds, this contribution uses the woody shrub Mimosa pigra L. (mimosa) as a case history to examine the methodology of classical biological control and the reasons for the widely accepted 75% failure rate. Overall objectives are for all biocontrol agents to have the opportunity to fully express their potential and to insure that limited resources are spent wisely on attainable weed control. The three main conclusions were that (1) the premises on which biocontrol is based has restricted advancement of this method; (2) monitoring is the logical first step to improving the selection of agents and release sites; and (3) it may be more cost-effective to introduce fewer agents that have undergone agent/plant and host/home range pre- and post-release ecological studies. Weed control may remain elusive unless advantage is taken of every beneficial result. Innovative assistance to agents and the integration of different control methods may preserve a role for weed biological control and has the potential to be of great importance for future weed management. It is proposed that the climate in the Top End of the Northern Territory and the lack of competition on the floodplains has contributed to mimosa's invasiveness. Climate may also underly the difficulties faced by agents. Agents appear unable to impart effective control in the dry season because of low numbers which relates to mimosa's poor growth; nor in the wet season, when the impact from high numbers of agents is outstripped by mimosa's growth.