Nutritional resources used by the invasive maize pest Diabrotica virgifera virgifera in its new South-east-European distribution range

Food utilization by adults of the invasive maize (Zea mays L.) (Poaceae) pest western corn rootworm (WCR; Diabrotica virgifera virgifera LeConte) (Coleoptera: Chrysomelidae) was investigated in the south‐eastern part of its new European distribution range. At weekly intervals over a 10‐week period, 10 beetles per field were collected from six fields that had a high abundance of flowering weeds and six fields with a low abundance of flowering weeds, with the aim of understanding adult feeding behaviour in Europe and comparing this behaviour with North American WCR. Gut content analysis was performed to determine the use of maize tissue and weed pollen with regard to maize phenology. Furthermore, all pollen found within the gut was quantified and identified to plant species level. The use of maize tissue by adult WCR changed over time according to maize phenology. Pollen originating from plants other than maize was used more frequently as the maize matured. Adults fed on pollen from 19 of 25 different plant species found in maize fields and showed a preference for the pollen of specific weeds. Pollen from weed species was found more often in beetles from fields with a high abundance of weeds compared to beetles from fields with a low abundance of weeds. Females consumed greater amounts of pollen than males, the latter feeding on a wider diversity of host plants. The pollen resources used by adult WCR in Hungary were more diverse compared to WCR in the USA, which may contribute to the invasion success of WCR in Europe.     

Sources of variation in pollinator contribution within a guild: the effects of plant and pollinator factors

Among plants visited by many pollinator species, the relative contribution of each pollinator to plant reproduction is determined by variation in both pollinator and plant traits. Here we evaluate how pollinator movement among plants, apparent pollen carryover, ovule number, resource limitation of seed set, and pollen output affect variation in contribution of individual pollinator species to seed set in Lithophragma parviflorum (Saxifragaceae), a species visited by a broad spectrum of visitors, including beeflies, bees and a moth species. A previous study demonstrated differences among visitor species in their single-visit pollination efficacy but did not evaluate how differences in visitation patterns and pollen carryover affect pollinator efficacy. Incorporation of differential visitation patterns and pollen carryover effects —commonly cited as potentially important in evaluating pollinator guilds — had minor effects (0–0.6% change) on the estimates of relative contribution based on visit frequency and single-visit efficacy alone. Beeflies visited significantly more flowers per inflorescence than the bees and the moth. Seed set remained virtually constant during the first three visited flowers for beeflies and larger bees, indicating that apparent pollen carryover did not reduce per-visit efficacy of these taxa. In contrast, Greya moth visits showed a decrease in seed set by 55.4% and the smaller bees by 45.4% from first to second flower. The larger carryover effects in smaller bees and Greya were diminished in importance by their small overall contribution to seed set. Three variable plant traits may affect seed set: ovule number, resource limitation on seed maturation, and pollen output. Ovule number per flower declined strongly with later position within inflorescences. Numbers were much higher in first-year greenhouse-grown plants than in field populations, and differences increased during 3 years of study. Mean pollen count by position varied 7-fold among flowers; it paralleled ovule number variation, resulting in a relatively stable pollen:ovule ratio. Resource limitation of seed set increased strongly with later flowering, with seed set in hand-pollinated flowers ranging from 66% in early flowers to 0% in the last two flowers of all plants. Variation in ovule number and resource limitation of seed maturation jointly had a strong effect on the number of seeds per flower. Visitation to early flowers had the potential to cause more seed set than visitation to later flowers. Overall, the most important sources of variation to seed production contribution were differences among pollinators in abundance and absolute efficacy (ovules fertilized on a single visit) and potentially differential phenology among visitor species. These effects are likely to vary among populations and years.     

基于山地蜂蜜花粉组成的中华蜜蜂传粉多样性研究

中华蜜蜂为多种植物传粉,具有重要的生态服务价值。为进一步了解中华蜜蜂选择蜜粉源植物的多样性与特征,采用聚合酶链式反应(PCR)、DNA条形码、高通量测序等技术,研究了源自陕西宝鸡、贵州望谟和广西凤山蜂巢蜜中的花粉来源。通过对样品花粉rbcL基因片段扩增及测序、分析,发现各样本间可操作分类单元(OTU)水平上蜜粉源植物Alpha多样性指数无显著差异,同一地点样品不同重复间存在较高的相关性,而不同地区样本相关性较低。三地共鉴定出27目46科71属82种蜜粉源植物,其中宝鸡市、望谟县、凤山县样本中分别鉴定出57种、30种和40种,各地蜜粉源植物的物种组成存在较大差异。这些蜜粉源植物中,菊目植物种类最多,其次为毛茛目,分别有12种和7种。其中草本植物和木本植物(含乔木、灌木和木质藤本等)分别有44种和38种。研究对蜜粉源植物花序特点进行了分析,但并未发现相关性状对中华蜜蜂选择具有的影响。从属的区系成分分析,总体上温带分布区类型的植物属多于热带分布区类型的属,所占比例分别为46.5%和36.6%,但在凤山县样本中出现热带分布区类型多于温带分布区类型的情况。在不同样品中,红足蒿(Artemisia rubripes)、向日葵(Helianthus annuus)、芜青(Brassica rapa)、粗糠柴(Mallotus philippensis)、枇杷(Eriobotrya japonica)等分别占有一定优势,其与中华蜜蜂的关系值得进一步研究。根据蜜粉源植物的系统进化关系,中华蜜蜂访问的蜜粉源植物处于不同进化地位的分支,其中在菊类分支和蔷薇类分支比较集中。研究揭示了中华蜜蜂传粉植物组成特点,为进一步认知中华蜜蜂传粉服务功能的重要性提供依据。     

Seasonal variation of collected pollen loads of honeybees (Apis mellifera L. anatoliaca)

Pollen collected by honeybees foraging in the region of Bursa, Turkey was analysed for a whole year. Pollen loads were collected from the hives of Apis mellifera anatoliaca once a week and were classified by colour. Forty‐one taxa were identified from the pollen analyses of the loads and 14 of these had percentages higher than 1%. Only 2.05% of the total pollen could not have been identified. Dominant taxa include; Brassicaceae (11.19%), Helianthus annuus L. (10.84%), Cichorioideae (8.93%) Salix spp. (7.99%), Rosaceae (7.37%), Centaurea spp. (7.56%), Papaver spp. (7.41%), Knautia spp. (6.99%), Fabaceae (6.01%), Asteraceae (5.73%), Xanthium spp. (2.65%), Chrozophora spp. (2.45%), Plantago spp. (1.56%) and Acer spp. (1.54%) representing 88.23% of the total. Distinct variations in plant usage are seen through the year with initial use of Rosaceae, Salix, and to a lesser extent Brassicaeae. As these groups finish flowering the bees move onto Helianthus annuus, Centaurea through the summer followed by Asteraceae in the late summer and Fabaceae in the autumn. There is a strong reliance on crop species for pollen forage but a number of indigenous species are also seen within the samples. The most productive period for collecting various pollen types, and the ideal period to determine pollen preferences of honey bees was June‐August.     

Pollen amino acids—an additional diet for a nectar feeding butterfly?

The increase of the amino acid concentration over different time intervals in artificial nectar (i.e., a sucrose solution) due to pollen contamination was investigated in four Californian plant species (Aesculus californica, Amsinckia lunaris, Brodiaea pulchella, Carduus pycnocephalus), which are important nectar resources for a Californian colony of the butterflyBattus philenor as well as for other insects. The increase of the amino acid concentration in the medium is different in all four species and seems to be determined by a variety of factors including permeability of the pollen grain wall and presence or absence of pores. The results suggest a passive diffusion process of the free pollen amino acids into the medium rather than an active release. Implications from the experiments forBattus philenor and for other nectar feeding pollinators are discussed. A possible complementary effect of free pollen and nectar amino acids is proposed for plant species in which pollen is likely to be knocked into nectar by their flower visitors. A possible evolutionary pathway from nectar feeding butterflies such asBattus philenor to the complex derived pollen feeding habit in theHeliconius butterflies is proposed.     

Partitioning of pollen resources by two stingless bee species in the north Bahia,Brazil

Analysing the pollen stored by stingless bees allows identification of the diversity of flowering plants visited by these bees while collecting resources during a given period. However, few studies have focused on investigating the sharing of resources between species of native bees that coexist in transitional plant formations, which support conservation efforts and increase colony productivity. This study aims to describe the partitioning of pollen resources among colonies of two species of stingless bees in the state of the Bahia (Brazil) through the analysis of stored pollen. The study was conducted in neighbouring vegetation zones of the relevant species Melipona quadrifasciata anthidioides and Melipona scutellaris by collecting monthly pollen samples stored by three colonies of each species over one year. The collected samples were treated using the acetolysis technique, and the partitioning of pollen resources between the two species was investigated through quali-quantitative analysis of the treated pollen. The results show that among the 16 pollen types belonging to a particular species or group identified in the Melipona quadrifasciata anthidioides samples and the 18 identified in the Melipona scutellaris samples, 13 were shared by both species. The two most common pollen types stored by both species were from Mimosa arenosa (Fabaceae, Mimosoidae) and Eucalyptus sp. (Myrtaceae). These results demonstrate the niche similarity of pollen pasture between these two species and suggest that conservation efforts for these bee species should focus on the plant families most visited by bees.     

Biological aspects and life table parameters of the predacious mite,Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) consuming food types during immature stages and after adult emergence

To investigate the effect of food types on biological aspects and life table parameters of the predacious mite, Neoseiulus californicus (McGregor), immature stages were fed on pollen of maize, Zea mays L. and eggs of Tetranychus urticae Koch, while adult females were offered the same foods and the alternate shift of each food. All individuals of predator females reached adulthood when reared on maize pollen and prey eggs, but their life cycle was significantly longer on pollen than on prey. The shortest preoviposition period of N. californicus occurred after continuous feeding on T. urticae eggs, whereas the longest happened when fed on prey eggs switched to maize pollen. Continuous consuming of maize pollen showed the longest ovipositoin period for the predator, while rearing on maize pollen shifted to prey eggs exhibited the shortest duration. The longest longevity and highest sex ratio of females to total in N. californicus were recorded when continuously utilised pollen, whereas the shortest longevity and lowest sex ratio were noted when continuously consumed prey. On the contrary, the egg production and life table values of the predator were the highest by continuous feeding on prey eggs, while they were the lowest by continuous rearing on maize pollen. Therefore, feeding juveniles on prey eggs and adult females on maize pollen is better for long-term preservation of N. californicus females than continuous feeding on maize pollen due to a shorter developmental duration, a higher egg production and more favourable life table values.     

基于DNA条形码的白斑切叶蜂粉源植物种类及多样性分析

利用人工蜂巢收集白斑切叶蜂(Megachile strupigera)蜂粮样本,并通过克隆测序方法,比较分析了新余市水北镇(XYSB)、吉安市戈坪乡(JAGP)、赣州市沙地镇(GZSD)和赣州市齐云山自然保护区(GZQYS)的4种不同林地类型的白斑切叶蜂粉源植物组成及多样性。共鉴定出粉源植物9科10属15种。其中黄荆Vitex negundo和山牡荆Vitex quinata为优势种。Chao1指数、Shannon-wiener指数和Simpson指数分析结果表明,4个样地粉源植物的丰富度和多样性依次为GZQYSGZSDXYSBJAGP。并且,4个样地七月上旬的物种丰富度均明显高于八月中旬。同一时期的粉源植物种类及多样性存在显著差异,表明不同林地利用方式对白斑切叶蜂粉源植物多样性的影响非常明显,并随人为干扰程度的增高而降低。相同样地中2个不同时期均呈现出粉源植物多样性随花期变化而降低的趋势,但其主要粉源植物种类没有发生改变,表明该蜂主要粉源植物没有受到花期变化的影响。因此,黄荆和山牡荆是白斑切叶蜂的主要粉源植物,对维持白斑切叶蜂种群的稳定具有重要作用。     

Pollen feeding,resource allocation and the evolution of chemical defence in passion vine butterflies

Evolution of pollen feeding in Heliconius has allowed exploitation of rich amino acid sources and dramatically reorganized life‐history traits. In Heliconius, eggs are produced mainly from adult‐acquired resources, leaving somatic development and maintenance to larva effort. This innovation may also have spurred evolution of chemical defence via amino acid‐derived cyanogenic glycosides. In contrast, nonpollen‐feeding heliconiines must rely almost exclusively on larval‐acquired resources for both reproduction and defence. We tested whether adult amino acid intake has an immediate influence on cyanogenesis in Heliconius. Because Heliconius are more distasteful to bird predators than close relatives that do not utilize pollen, we also compared cyanogenesis due to larval input across Heliconius species and nonpollen‐feeding relatives. Except for one species, we found that varying the amino acid diet of an adult Heliconius has negligible effect on its cyanide concentration. Adults denied amino acids showed no decrease in cyanide and no adults showed cyanide increase when fed amino acids. Yet, pollen‐feeding butterflies were capable of producing more defence than nonpollen‐feeding relatives and differences were detectable in freshly emerged adults, before input of adult resources. Our data points to a larger role of larval input in adult chemical defence. This coupled with the compartmentalization of adult nutrition to reproduction and longevity suggests that one evolutionary consequence of pollen feeding, shifting the burden of reproduction to adults, is to allow the evolution of greater allocation of host plant amino acids to defensive compounds by larvae.     

Ambrosia pollen in the air of Lublin, Poland

Studies on Ambrosia pollen concentrations were carried out in Lublin in the period 1995–2004. The effects of a number of meteorological factors were analysed. In the first period of the study, the gravimetric method was used (1995–1999), while in the second period, the volumetric method was applied. The results show an increasing trend in the amount of airborne pollen. The Ambrosia pollen season in Lublin lasts from August to October. Over a period of 5 years, the highest number of pollen grains was recorded in September (53%), followed by August (44%) and October (3%). There were wide variations in annual totals. The annual total pollen counts was 167–1180 grains, with the peak value in 2002. Maximum daily pollen concentrations (56–312 pollen grains m⁻³) were recorded in the first half of August and in the first half of September. On the days when high Ambrosia pollen concentrations occurred, the temperature was above 21°C and the winds were mainly from the southeast, south and east. Maximum intradiurnal concentrations of pollen grains occurred in the afternoon hours. These results indicate, to some degree, that Ambrosia pollen is transported for long distances before descent.     

History of vegetation and land use from 3200 B.P. to the present in the north-west Burren,a karstic region of western Ireland

A radiocarbon-dated pollen profile provides the first evidence for the vegetation history of the north-west Burren, a karstic region in Co. Clare, western Ireland. The profile, which spans the period ca. 3200-0 B.P., shows that Corylus was the main woody species and that, apart from the later eighteenth and nineteenth centuries, when woody species were almost totally cleared, it constituted a more important element in the landscape than at present. The data indicate that small populations of Quercus, Fraxinus, Betula, Alnus and possibly Ulmus were also present until at least the mid seventeenth century. Exceptionally high values of Plantago lanceolata (mostly in excess of 20% total terrestrial pollen) suggest intensive pastoral farming over most of the period. Between A.D. 200–580, a lull in activity is recorded during which woody species and, in particular, hazel scrub regenerated. The separation of pollen of cereal origin from large cereal-type pollen produced by non-cultivated grasses proved particularly problematic. Reliance has therefore been placed on the weed pollen flora as a guide to arable activity. This flora indicates that arable farming was of some importance in the Burren from A.D. 1000 onwards. The implications of the various findings for the longer term history of the rarer elements of the Burren flora and the relationship between the pollen record and the archaeological and historical evidence for settlement and land use are discussed.     

Pollen movement to flowering canopies of pistillate individuals of three rain forest tree species in tropical Australia

This study measured the quantities of effective pollen vectors and their pollen loads arriving at the canopies of dioecious tropical rain forest trees in north-east Queensland. Population flowering synchrony, effective pollinator populations and pollen loads transferred between staminate and pistillate trees were compared among three insect-pollinated tree species. All three were visited by a wide range of insects, 75% of which (mostly 3–6 mm long) carried conspecific pollen. Fewer than 8% of individual insects were found to be carrying single-species pollen exclusively and none could be described as specialist pollen foragers. The introduced honeybee carried greater quantities of pollen than any native species but was not necessarily a reliable pollinator. The brief flowering periods in Neolitsea dealbata (3–4 weeks) and Litsea leefeana (4–5 weeks) populations were synchronized among individuals. Flowering in the Diospyros pentamera population extended over 15 weeks and most individuals were in flower for most of this period. Staminate trees began flowering earlier, produced more flowers and attracted relatively more insects than did pistillate trees, suggesting a density-dependent response of pollinators to flowering performance. Pollen was trapped in greater quantities on insects at staminate trees than at pistillate trees. Insect numbers increased at peak flowering periods and Diptera were the most abundant flower visitors. Anthophilous Coleoptera were more numerous at staminate than at pistillate trees in all three tree species populations. Larger quantities of pollen were mobilized during peak flowering times although the greatest quantities were transferred to pistillate canopies towards the end of the population flowering periods. Diptera carried pollen more often to pistillate N. dealbata and L. leefeana trees than did other groups whereas Coleoptera carried pollen more often to pistillate D. pentamera trees. The two contrasting flowering performances in the three tree species are discussed with reference to mechanisms that facilitate pollen transfer between staminate and pistillate trees.     

A calendar for tree pollen in London

Data from a pollen monitoring network in Islington, North London, are used to construct tree pollen calendars for the tree seasons 1987 to 1989 inclusive. Annual variations in the pollen abundance and length of flowering season are investigated for individual species in relation to meteorological factors and the inherent biological rhythms of trees. Results indicate clear relationships between seasonal variations in pollen abundance and the weather, both in the prevailing season and also in the preceeding year during the time of pollen formation. Annual variations evident in the pollen records for Betula and Quercus support the theory of inherent biennial cycles for these species. Patterns for other trees do not show clear trends within the period sampled. Insufficient information is available to determine the concentration thresholds of allergic response for most tree pollens, but evidence from Finland is used to identify the timing and duration of periods which exceed the response thresholds for Betula.     

Adult feeding habits of three Perloidea species (Plecoptera: Perlidae and Chloroperlidae)

The gut content composition of three species of the superfamily Perloidea, Marthamea selysii (Pictet, 1842), Dinocras cephalotes (Curtis, 1827), and Siphonoperla torrentium (Pictet, 1842), from northwestern Spain is analyzed and described. The quantity of food found in all adults of M. selysii and D. cephalotes was very low. Spores of fungi and pollen of angiosperms were the most abundant components in the diet of M. selysii. Pollen of angiosperms, followed by fungal spores, detritus, and animal matter were the most abundant components in the diet of both sexes of D. cephalotes. The adult diet of both sexes of S. torrentium consists mainly of pollen and agrees with data of the previous studies on this same species in other areas. Our results also show that the consumption of animal matter could be a way to get a nutritional complement and is more common than previously considered in adult stoneflies. The obtained data support the hypothesis that adult feeding is less important for large stoneflies (as M. selysii and D. cephalotes) than for other smaller Perloidea (as S. torrentium), but feeding habits in these large Plecoptera could not be as negligible as previously supposed.     

Adult diet affects lifespan and reproduction of the fruit‐feeding butterfly Charaxes fulvescens

Fruit‐feeding butterflies are among the longest lived Lepidoptera. While the use of pollen‐derived amino acids by Heliconius butterflies has been interpreted as important for the evolution of extended lifespans, very little is known about the life‐history consequences of frugivory. This issue is addressed by investigating effects of four adult diets (sugar, sugar with amino acids, banana, and moistened banana) on lifespan and reproduction in the fruit‐feeding butterfly Charaxes fulvescens Aurivillius (Lepidoptera: Nymphalidae). Female butterflies were collected from Kibale National Park, Uganda, and kept individually in cages near their natural habitat and data were collected on lifespan, oviposition, and hatching of eggs. Lifespan in captivity was longer for the sugar and the amino acid cohort, than for the banana cohorts. The longitudinal pattern of oviposition was erratic, with many days without oviposition and few periods with high numbers of eggs laid. Butterflies typically did not lay eggs during their 1st week in captivity and the length of the period between capture and first reproduction was significantly shorter for butterflies fed moistened banana. The length of the reproduction period (first reproduction–last reproduction in captivity) and the reproduction rate (total number of eggs/length of the reproduction period) did not differ significantly between the diet treatments. Those fed with amino acid and moistened banana had significantly higher egg hatchability than those fed with sugar and banana. We found no evidence for a lifespan cost of reproduction. Our results show that (1) female C. fulvescens can use amino acids in their diet for laying fertile eggs, (2) more wing‐wear does correlate with lower survival in captivity (indicating aging in the wild), but not with intensity of reproduction (providing no evidence for reproductive aging), and (3) fruit‐feeding butterflies may be dietary restricted in the field.     

Aerobiology of Vigo, North-Western Spain: atmospheric pollen spectrum and annual dynamics of the most important taxa, and their clinical importance for allergy

Vigo is a city located in the northwest of the Iberian Peninsula. Influenced by the Atlantic climate, it is surrounded by a Eurosiberian-type vegetation, modified by the introduction of forestry and ornamental species. Different ruderal vegetation types, resulting from human influence, grow in the area. The study of the pollen content of the air of Vigo started in 1989, with a Cour trap. Average results for the period 1989–1995 are presented in this paper, together with the lowest and highest values found. The representativeness of the mean values is analysed by calculating the coefficient of variation of the data series. Most pollen types in the atmosphere of Vigo are from tree species (54.2%); an important proportion comes from herb species (43.9%) and very few (1.8%) correspond to shrub species. A total of 73 different pollen types have been identified. The most abundant, listed in decreasing order of mean annual values for the period, are:Pinus (25.1%), Poaceae (21.1%), Urticaceae (14.6%),Quercus (8.5%),Castanea (3.7%),Betula (3.6%),Eucalyptus (3.4%),Plantago (3.2%),Alnus (2.1%), Cupressaceae (2.1%), Oleaceae (1.6%;Olea 1.3%),Platanus (1.3%),Rumex (1.3%), Chenopodiaceae/Amaranthaceae (1.0%), Ericaceae (0.8%), Asteraceae (0.6%;Artemisia 0.1% andTaraxacum type 0.2%) andMercurialis (0.5%). A pollen calendar showing the annual dynamics of all these pollen types is presented in this paper. A parallel study of the clinical importance of respiratory allergies in Vigo was also conducted. From a sample of 2750 patients, 87.2% suffered from rhinoconjunctivitis, 26.0% of these due to pollen, and 78.3% from asthma, 17.2% due to pollen. The pollen types responsible for these allergies, listed in decreasing order, are: Poaceae (78%),Parietaria (12%),Chenopodium (11%),Plantago (9%), Oak (4%),Artemisia (3%),Pinus (3%),Eucalyptus (3%),Olea (2%),Platanus (2%),Castanea (2%),Taraxacum (2%),Rumex (2%),Betula (1%),Cupressus (1%) andMercurialis (1%).     

Seasonal variation in vegetation and pollen collected by honeybees in Thessaloniki,Greece

Pollen is important for the nutrition of honeybees and it is necessary for their survival and reproduction. In this study, we collected daily the pollen pellets from four colonies and also recorded the plants in flower in the area around the apiary, over a two‐year period. Field records revealed the presence of 204 species with Asteraceae, Fabaceae and Rosaceae being the most specious families. Although honey bees collected more than 140 pollen types, the main pollen sources (>60% of the total weight) came from less than ten taxa. The most important pollen types with respect to total weight were Sisymbrium irio, Papaver rhoeas, Verbascum sp., Polygonum aviculare, Zea mays and Olea europaea. The use of pollen traps proved a more accurate method to record the type and the foraging period during which the honeybees collect pollen, compared to field observations.     

Host-plant influence on the population ecology of the jack pine budworm, Choristoneura pinus (Lepidoptera: Tortricidae)

Abstract.

• 1 Newly-emerged, second-instar jack pine budworm (Choristoneura pinus Freeman) establish spring feeding sites preferentially in the pollen cones of their host tree, Pinus banksiana Lamb.
• 2 Laboratory studies showed that the rate of establishment and survival of jack pine budworm on pollen cones was high throughout the entire spring emergence period of the insect.
• 3 In contrast, the rate of establishment and survival of jack pine budworm on vegetative buds was very poor early in the spring. Vegetative buds were only acceptable as feeding sites to the jack pine budworm for a relatively brief period in late spring.
• 4 Field studies showed that the change in population density of jack pine budworm during the spring emergence stage, as expressed by k-values, was a function of the abundance of pollen cones in the stand. Population reduction was greatest in those stands with the fewest pollen cones.
• 5 Direct measurement of spring dispersal by jack pine budworm showed that dispersal and consequent losses to the budworm population were greatest in stands with the fewest pollen cones.
• 6 We conclude that changes in the density of jack pine budworm are strongly influenced by production of pollen cones in the host stand. Because pollen cone production is related to previous years of defoliation by the jack pine budworm, we propose that pollen cones act as a density-dependent factor governing the density of early-stage jack pine budworm.
• 7 The resulting dynamics are compared to those of other budworm species and used to explain observed regional and temporal patterns of jack pine budworm outbreaks.

     

Seasonal variations in food resource partitioning among four sympatric gudgeon species in the upper Yangtze River

Knowledge of food resource partitioning among sympatric fish species is crucial for understanding the potential mechanisms of species coexistence. Gudgeons (Teleostei: Cyprinidae: Gobioninae) often dominate fish assemblages in the upper Yangtze River. However, little research has been conducted on their trophic interactions. In this paper, seasonal diet and feeding strategy variations of four sympatric gudgeon species, Coreius guichenoti, Coreius heterodon, Rhinogobio ventralis, and Rhinogobio cylindricus, were investigated by analysis of intestinal tract contents, aiming to explore whether food resource partitioning occurred among them. Fish specimens were collected during spring (April–May) and autumn (August–October) in 2010 in Hejiang, a free‐flowing stretch of the upper Yangtze River. Coreius guichenoti, C. heterodon, and R. cylindricus showed omnivorous feeding habits, while R. ventralis exhibited an obligate carnivore feeding habit. Diet overlap among the four studied species was high, especially in spring. However, changes in feeding strategies were observed in autumn. Specifically, C. guichenoti and R. cylindricus expanded their dietary niche breadth and consumed detritus, Sinopotamidae or Hydropsychidae as important complementary food resources. In contrast, C. heterodon and R. ventralis reduced their dietary niche breadth and became more specialized on mussels (Limnoperna lacustris). These results confirmed that sympatric fish species can coexist with high diet overlap, and food resource partitioning among these species may also fluctuate with the seasons.     

Spatial predictability and resource specialization of bees (Hymenoptera: Apoidea) at a superabundant, widespread resource

For reciprocal specialization (coevolution) to occur among floral visitors and their host plants the interactions must be temporally and spatially persistent. However, studies repeatedly have shown that species composition and relative abundance of floral visitors vary dramatically at all spatial and temporal scales. We test the hypothesis that, on average, pollen specialist bee species occur more predictably at their floral hosts than pollen generalist bee species. Taxonomic floral specialization reaches its extreme among species of solitary, pollen-collecting bees, yet few studies have considered how pollen specialization by floral visitors influences their spatial constancy. We test this hypothesis using an unusually diverse bee guild that visits creosote bush (Larrea tridentatd), the most widespread, dominant plant of the warm deserts of North America. Twenty-two strict pollen specialist and 80 + generalist bee species visit Larrea for its floral resources. The sites we sampled were separated by 0.5 to > 1450 km, and spanned three distinct deserts and four vegetation zones. We found that species of Larrea pollen specialist bees occurred at more sites and tended to be more abundant than generalists. Surprisingly, spatial turnover was high for both pollen specialist and generalist bee species at all distances, and species composition of samples from sites 1–5 km apart varied as much as repeat samples made at single sites. Nevertheless, the pattern of bee species turnover was not haphazard. As distance among sites increased faunal similarity of sites decreased. Faunal similarities among sites within 250 km of each other were generally greater than if randomly distributed over all sites (the null model). No single ecological category of species (widespread, localized, Larrea pollen specialist, floral generalist) accounted for this spatial predictability. Evidently, concordant local distribution patterns of many ecologically diverse species contribute to the non-random spatial pattern. The ecological dominance of creosote bush does not confer obvious ecological advantages to its specialist floral visitors. Spatial turnover is comparable to that found for bee guilds from other biogeographic regions of the world and is not therefore limited to those bee species that inhabit highly seasonal climates, such as deserts. Philopatry and differences in bloom predictability among sites are probably more important causes for spatial turnover of bee species than are interspecific competition for nest sites or floral resources.