南京地区外来植物一年蓬上访花昆虫的多样性及其访花选择性的影响因素分析

为揭示外来植物一年蓬Erigeron annuus上的本土访花昆虫多样性和影响访花行为的因素, 本研究在南京郊区进行了连续2年的野外调查, 采用跨栏模型分析了环境因素如何影响昆虫的访花选择性, 即接受概率（测度是否接受一年蓬花）和访问频数（测度接受一年蓬花的程度）。调查发现, 访问一年蓬花的昆虫共计9目54科145种, 其中, 科丰富度占优势的是膜翅目、 鳞翅目和鞘翅目（均占总科数的20.75%）, 其次是双翅目（18.87%）和半翅目（13.21%）; 物种丰富度占优势的是双翅目（26.39%）, 其次是膜翅目（18.75%）、 半翅目（18.75%）、 鞘翅目（17.36%）和鳞翅目（15.38%）。多数目的物种丰富度在6-7月最高, 9月最低, 仅双翅目（食蚜蝇为主）在5月最高。运用跨栏模型对物种优势度最大的半翅目、 膜翅目和双翅目等的访花个体数量及其影响因素的分析结果表明： 影响半翅目和膜翅目对一年蓬花访问倾向（接受概率）的因素多于影响其访问频数的因素, 由此预测这些访花昆虫可能参考较多因素做出是否接受一年蓬花, 而依据较少线索做出访问程度的访花行为决策; 一年蓬植株密度影响半翅目和膜翅目昆虫的接受概率, 而花密度影响半翅目和双翅目昆虫的接受概率和访问频数, 说明靶标植物花的特性可能对访花昆虫的访花行为决策起主要作用。     

大叶醉鱼草访花昆虫行为与活动规律

于2009年4～9月对云南农业大学苗圃内栽植的大叶醉鱼草访花昆虫进行观察。结果表明,大叶醉鱼草的访花昆虫有63种,隶属双翅目、半翅目、膜翅目、鳞翅目、鞘翅目、革翅目和螳螂目;食蚜蝇科为大叶醉鱼草种群的主要传粉昆虫;不同月份访花昆虫的种类不同;天气变化会影响访花昆虫的种类和数量;同一天内不同时间,访花昆虫的访花频率有差异,一般每天12:00～16:00的访花频率最高。     

Flowering and seasonal changes in flower sex ratio and frequency of flower visitors in a population of Saxifraga hirculus

The open, dish-shaped flowers of Saxifraga hirculus reflected ultraviolet and yellow light, contained very small amounts of nectar, and contained an average of about 75300 pollen grains per flower. Almost 11% of the pollen was inviable. Stigmatic pollen loads and seed set decreased during the course of the season. The plant appeared to be fully between-ramet compatible and partially within-ramet compatible. Seed set for the population was 30.3%. The protandrous flower opened during the day and had male and female phases of nine and three days, respectively. The protandrous system reduced the number of pollination days by a third.
At least 26 species of insects, 16 of which were syrphids, visited the flowers. Based on the number of flower visits, four species were the dominant visitors of S. hirculus: Eurimyia lineata and Neoascia tenur (Diptera: Syrphidae); Asindulum nigrum (Diptera: Mycetophilidae), and Zygaena trlfolii (Lepidoptera: Zygaenidae). Eurimyia lineata was the most frequent visitor (51% of all visits). As the season advanced, the visits by E. lineata decreased, whereas the visits by A. nigrum increased. Z. trifolli disappeared completely towards the end of the season. Only two thirds of the pollination days were "good" foraging days for these visitor species. The four major visitor species spent an average of 11.7, 27.4, 30.7 and 22.6 s per flower, respectively. Estimates suggest that about 6.5 visits (which is equal to 2.6 min of flower-visiting) and 2100 grains of pollen were required to produce one seed.     

A checklist of arthropods associated with pig carrion and human corpses in southeastern brazil

Necrophagous insects, mainly Diptera and Coleoptera, are attracted to specific stages of carcass decomposition, in a process of faunistic succession. They are very important in estimating the postmortem interval, the time interval between the death and the discovery of the body. In studies done with pig carcasses exposed to natural conditions in an urban forest (Santa Genebra Reservation), located in Campinas, State of S?o Paulo, southeastern Brazil, 4 out of 36 families of insects collected - Calliphoridae, Sarcophagidae, Muscidae (Diptera) and Dermestidae (Coleoptera) - were considered of forensic importance, because several species were collected in large numbers both visiting and breeding in pig carcasses. Several species were also observed and collected on human corpses at the Institute of Legal Medicine. The species belonged to 17 different families, 6 being of forensic importance because they were reared from human corpses or pig carcasses: Calliphoridae, Sarcophagidae, Muscidae, Piophilidae (Diptera), Dermestidae, Silphidae and Cleridae (Coleoptera). The most important species were: Diptera - Chrysomya albiceps, Chrysomya putoria, Hemilucilia segmentaria, Hemilucilia semidiaphana (Calliphoridae), Pattonella intermutans (Sarcophagidae), Ophyra chalcogaster (Muscidae), Piophila casei (Piophilidae); Coleoptera - Dermestes maculatus (Dermestidae), Oxyletrum disciolle (Silphidae) and Necrobia rufipes (Cleridae).     

上海临港新城河岸带昆虫群落特征

临港新城是上海大都市圈中一个快速城市化的滨海城区。为掌握临港新城河岸带在快速城市化下昆虫群落的特点,2009年10月—2010年9月对临港新城河岸带昆虫分不同生境及不同季节进行了调查,共获得昆虫7755头,隶属于13目、84科、199种。该区域河岸带昆虫优势类群为半翅目(Hemiptera)、双翅目(Diptera)和膜翅目(Hymenoptera)昆虫,分别占总数的37.7%、23.5%和16.5%;水生昆虫种类数及个体数分别占所调查昆虫的12.1%和11.2%;从Shannon多样性指数看,人工林昆虫多样性最高为1.73,其他生境依次为次生林(1.69)>绿地(1.48)>荒地(1.46)>农田(1.42);季节动态变化和生境类型对昆虫的数量、种类、丰富度和均匀度影响较大;该区域河岸带昆虫依食性可分为6类:植食性、捕食性、寄生性、腐食性、杂食性和访花昆虫,植食性昆虫种类和数量分别占62.8%和55.5%,其他食性的昆虫偏少,人类的干扰活动及河岸带景观植被对原有植被的破坏是主要原因。     

阿魏传粉昆虫及其访花行为的初步研究

对新疆阿魏访花昆虫种类、昆虫访花频次、昆虫访花时间及昆虫访花行为进行了初步研究。在盛花期观察中,(1)发现有5目、23科、45种昆虫进行了访花,其中传粉昆虫4科7种,均属蜜蜂总科;(2)各类昆虫访花频次在不同观察时间变化较大,传粉蜜蜂仅出现在其中一个观察日中;(3)不同种类昆虫在花上的停留时间差异很大,传粉昆虫停留时间很短,鞘翅目昆虫停留时间最长。进入始果期后,昆虫的访花行为是围绕花盘的蜜腺展开的。     

Insects Associated with Pig Carrion in Two Environments of the Brazilian Savanna

Studies of carrion fauna have increased in Brazil and have contributed to the knowledge of this fauna in the national territory. Brazil has continental dimensions and presents various biomes in its territorial area. Most of the carrion fauna have seldom been studied, and this is especially true for the Savanna or “Cerrado.” The present research examined the fauna visiting carrion in two environments and two seasons in a rural area situated in a region of Cerrado in southeastern Brazil. The two environments studied were a pasture and a fragment of semi-deciduous forest. Samples were collected during the dry and humid seasons of the year. The study identified the diversity and relative abundance of species attracted to pig carcasses (Sus scrofa L.) exposed in each environment and season. Eight pig carcasses (10 ± 1 kg) were placed in traps, and adult insects attracted to the traps were collected during the decay of the carcasses. A total of 92,489 insects were collected during the experiments. The Diptera was the most frequent order (92.2%) represented by 27 families and at least 124 species. This was followed by Coleoptera (4.4%) represented by 14 families and at least 65 species. Sarcophagidae had the greatest diversity of species, followed by Muscidae and Calliphoridae. Several species were collected only during a specific period of the year or in a single environment. The results are important from an ecological point of view and for Medico-Legal Forensic Entomology.     

Pollination and breeding system of Eritrichium nanum (Boraginaceae)

 Flower development, pollination and breeding system of the high alpine cushion plant, Eritrichium nanum (Boraginaceae), were investigated in nine populations from the European Alps at altitudes of 2700 m–3200 m. Peak flowering period lasts longer than a month, from mid-June to the end of July. In contrast to statements in the literature that flowers are protogynous and nutlets remain in their calyx until spring we found a distinct protandry and nutlets being dispersed before mid-September. Various insects from 12 families, but mostly Diptera, frequently visited E. nanum flowers, with flies from the families Anthomyiidae and Muscidae being the predominant visitors. Under optimal conditions (max. solar radiation, min. wind force), visitation rates of 200 simultaneously observed flowers reached 32.5–46.7 insects per hour, i.e. 0.16–0.24 insects per flower per hour. However, the commonly observed Anthomyiidae and Muscidae clearly preferred the white-yellowish flowers of Saxifraga exarata and Saxifraga bryoides which are abundant at E. nanum sites and which are certainly also pollinated by species of these two fly families. The flowers of these Saxifraga species offer plenty of nectar and may compete for pollinators with E. nanum, when they are flowering in its proximity. However, various other insects like Pontia callidice and Psodos sp. (Lepidoptera) as well as Andrena sp. (Hymenoptera) and especially Eristalis tenax and closely related hoverflies showed a higher degree of flower constancy to E. nanum, often flying from a blue Eritrichium cushion to the next and hence causing outcrossing. The five fornices of E. nanum flowers which obstruct the tube containing stamens and nectar, are a feature which differs distinctly from the syndrome of fly-pollinated flowers with easily accessible nectar. Consequently pollination by flies in E. nanum seems to be caused mainly by the unfavorable ecological conditions at high altitudes, where flies are the most frequent insects. Bagging experiments showed that outcrossing and geitonogamy are the prevailing pollination modes, and autogamy, although possible, plays only a minor role. Received February 13, 2001 Accepted November 23, 2001     

The radiation of Calochortus: generalist flowers moving through a mosaic of potential pollinators

Few studies have surveyed the insects visiting flowers at many sites and for many related species. Calochortus , a genus of about 60 species with its center of diversity in California, has flowers with a wide range of appearances. Insects visiting Calochortus flowers in 25 species were censused at 40 sites. Visitors at coflowering plants were also censused at each site. Calochortus flowers attracted insects in several orders, especially beetles that feed at glands on the petals and bees that often collect pollen. Species in Calochortus section Calochortus had a somewhat narrower spectrum of visitors than species in section Mariposa . The diversity of visitor species at Mariposa flowers was often greater than the diversity at coflowering species. On the whole, Calochortus flowers seem to be generalists in terms of their pollinators. Differences in visitor assemblage were greater between Calochortus populations at different sites than between visitors to Calochortus versus coflowering species at a site. Nevertheless, there were always significant differences in the proportions of various insects at Calochortus versus coflowering plants. In addition, proportions of visitors also differed between species of Calochortus at the same site. Thus, Calochortus flowers have diverged in the visitors they attract, and evidently they have done so without permanently specializing (except to a limited degree at the sectional level). What we know of the radiation of Calochortus lilies is consistent with an interpretation of adaptive wandering through a spatiotemporal mosaic of pollinator communities.     

Attraction of Stomoxys sp. to various fruits and flowers in Mali

The attraction of three Stomoxys species to 26 fruits and 26 flowers of different plant species was investigated in two different sites in Mali during 2008. Stomoxys niger bilineatus Grunberg (Diptera: Muscidae) was attracted to a wider spectrum of species, significantly attracted by four fruits and eight flowers compared with control traps, whereas S. sitiens Rondani (Diptera: Muscidae) was attracted to six fruits and seven flowers of different plants, and S. calcitrans L. (Diptera: Muscidae) was only attracted to one fruit and three flowers. Cold anthrone assays showed a significantly higher prevalence of sugar feeding amongst all three species at the lagoon site than at the site near Mopti. The rhythm of activity study shows temporally separated blood- and sugar-feeding periods for S. niger bilineatus and S. sitiens, but not for S. calcitrans. A comparison between blood and sugar feeding throughout the day shows that sugar feeding activity is as frequent as blood feeding activity. Because not much is known about the preferred sugar sources for Stomoxys species in their natural habitats, the present study provides valuable information regarding the attraction capability of several plants with possible future implication for Stomoxys control strategies.     

The biodiversity of Diptera in Old World rain forest surveys: a comparative faunistic analysis

Aim Identify the taxonomic patterns and the relative importance of particular families of Diptera sampled in comparative biodiversity surveys carried out at seven rain forest locations. We test and quantify the contention that different trapping methods routinely target different families. We identify the south–north (and upland/lowland) patterns and generate a set of hypotheses concerning mechanisms underlying these patterns. Location Australia and Papua New Guinea. Methods A total of 28,647 Diptera collected using canopy knockdown, yellow pan (water) traps and Malaise traps have been sorted to 56 families following these surveys. Comparative analyses across sites from Lamington National Park in south‐east Queensland, Australia to the Kau Wildlife area in Madang Province, Papua New Guinea, of the dipteran assemblages, and separately, of the 14 families which collectively made up 95.8% of the sample, are presented. Results Ordination by multi‐dimensional scaling and analyses of variances showed that the three methods complemented each other in terms of target families and, together, sampled a large proportion of the expected fauna of these sites. Ordinations on a method‐by‐method basis permitted the identification of groups of sites and analyses of variance indicated which taxa differed significantly across these groups. Main conclusions Recurrent patterns and associated hypotheses about their generation emerge from the data. These mirror floristic differences and reflect the biogeographic history of the sites since the Miocene. Clear linkages between the lowland faunas of Papua New Guinea and northern Australia are evident and are reflected in the abundances of the Dolichopodidae, Empididae, Muscidae and Tipulidae (other groupings underlined the essential difference of the New Guinean fauna which had characteristic proportions of Cecidomyiidae, Chironomidae, Dolichopodidae, Phoridae and Psychodidae). A subtropical grouping of families was evident comprising, inter alia, Chloropidae, Mycetophilidae, Drosophilidae and Phoridae which was frequently linked with the higher elevation tropical fauna at Robson's Creek, Atherton Tablelands. The long isolated, high elevation, rain‐forested massif at Eungella, central Queensland often emerged as a unique entity in the analyses, characterized by the high numbers of and proportions of Chironomidae, Psychodidae, Tipulidae and Empididae. This study supports the case for the wider use of Diptera in biodiversity analyses, complementing extensive earlier analyses which have used, predominantly, large coleopteran assemblages. The results indicate the potential power of family‐level analyses at large geographical scales and contribute to the ongoing debate on ‘taxonomic sufficiency’.     

Do exotic bumblebees and honeybees compete with native flower-visiting insects in Tasmania?

Honeybees, Apis mellifera, have been introduced by man throughout the globe. More recently, other bee species including various bumblebees (Bombus spp.) have been introduced to several new regions. Here we examine the impacts of honeybees and the bumblebee, Bombus terrestris, on native flower-visiting insects in Tasmania. To assess whether native insects have lower abundance or are excluded in areas that have been colonised by exotic bees, we quantified the abundance, diversity and floral preferences of flower-visiting insects at sites where bumblebees and honeybees were present, and compared them to sites where they were absent. This was achieved by hand searches at 67 sites, and by deploying sticky traps at 122 sites. Honeybees were by far the most abundant bee species overall, and dominated the bee fauna at most sites. There was considerable niche overlap between honeybees, bumblebees and native bees in terms of the flowers that they visited. Sites where bumblebees were established had similar species richness, diversity and abundance of native flower-visiting insects compared to sites where bumblebees were absent. In contrast, native bees were more than three times more abundant at the few sites where honeybees were absent, compared to those where they were present. Our results are suggestive of competition between honeybees and native bees, but exclusion experiments are needed to provide a definitive test.     

Predators control post-fledging mortality in tawny owls, Strix aluco

Patterns of variation in plant–pollinator (p–p) systems in response to environmental variables have been the focus of much recent attention. We analyzed species diversity and generalization of interactions of flower visitors belonging to eight p–p networks along a steep rainfall gradient in NW Patagonia, Argentina. To our knowledge, this is the first published study that applies a humidity-gradient approach to p–p networks analysis. Throughout the gradient, we recorded 1232 interactions between 413 different animal species and 111 plant species. We found that (a) specialization measures showed no clear pattern of variation throughout the rainfall gradient, (b) the diversity of flower-visiting insects does not consistently respond to rainfall gradients along the gradient, and (c) as we predicted, flies dominated the wetter end of the gradient, while at the drier end bees prevailed. The lack of differences in diversity could be explained by the repeated cycles of species extinctions undergone in the past by the southern temperate forests, which dominate the wetter end of the gradient. A logistic model that related the flies' dominance of the visitor assemblage with latitude was good predictor of the average fly composition of the entire region, although we found major between-site variations in response to local environmental conditions. The replacement of flies by bees towards the drier end of the gradient seemed to repeat a worldwide pattern where flies dominate humid regions while bees attain their greatest abundance in xeric regions. Regional patterns in the structure of our p–p systems (composition of the visitor fauna) were better explained by altitudinal differences, while function (percentage of interactions established by each taxon) seemed to be more influenced by precipitation.     

The effect of the dung pad fauna on the emergence ofMusca tempestiva [Dipt.: Muscidae] from dung pads in southern France

The emergence ofMusca tempestiva Fallèn, from cow pads in southern France was reduced by a mean of 98% and 96% respectively in nine experiments concluded in 1979 and 1981, by the action of the complete dung fauna. Fauna emerging from dung pads and captured in simultaneous trapping using dung baited pitfall traps consisted of 13 Dipterous species (9 Muscidae, 2 Sepsidae and 2 Sphaeroceridae), 25 Coleopterous species (7 Scarabaeidae, 1 Geotrupidae, 2 Aphodiidae, 3 Hydrophilidae, 12 Staphylinidae), 3 Hymenopterous parasites and 1 species of macrochelid and 2 species of parasitoid mites carried phoretically by the dung beetles. The total number of insects and mites per trap was usually small. The Staphylinidae which included 4Aleochara species of whichAleochara tristits Gravenhorst andA. bipustulata (L.) are known parasitoids of Diptera pupae, and 6 predatory species, were the most abundant insects present. Whilst the overall abundance of insects and mites trapped was relatively low it is probable that the most important factor in the control ofM. tempestiva was the combined influence of the different elements making up the dung pad fauna.     

双翅目昆虫传粉研究进展

昆虫传粉不仅在自然生态系统中发挥着十分重要的作用,也和农业生态系统中产量密切相关。众所周知,膜翅目昆虫是最重要的传粉昆虫。双翅目昆虫分布广,物种多,数量大,也是一类十分重要的传粉昆虫,但其传粉作用未受到足够的重视。本文主要综述了双翅目传粉昆虫的主要种类、传粉效力、传粉特征、与植物的协同进化以及双翅目昆虫传粉的生态学意义。据记载双翅目昆虫中至少有71个科涉及虫媒种类,目前有资料显示访花昆虫类群中双翅目约有54 417种,按涉及的种数排序居于昆虫纲传粉昆虫目中第4位。尽管双翅目昆虫单次访问可携带花粉量相对较少(相比于膜翅目),但是较高访问速率及庞大的个体数量,保证了其作为有效传粉者的地位。传粉综合征能够有效揭示植物与传粉者的协同进化关系,尤其是对一些专化传粉现象(如五味子科-瘿蚊系统)和泛化传粉的深入研究,更加深了我们对协同进化的理解。就生态学意义而言,一方面双翅目传粉昆虫是膜翅目传粉昆虫的有益补充,另一方面在一些特殊环境中,双翅目昆虫具有不可替代的作用。当前传粉昆虫(包括双翅目)数量急剧下降,而且双翅目昆虫的传粉价值还利用较少。结合我国当前的研究现状提出了以下未来研究重点:1)加深双翅目传粉效力和适应意义的案例研究以明确双翅目昆虫在传粉体系中的地位;2)加强栖息地格局变化与昆虫多样性的研究以明确栖息地改变对昆虫的影响程度;3)梳理访花和传粉、专化传粉和泛化传粉等关系以更加明确双翅目昆虫在与植物协同进化中的作用;4)逐步深入探讨花粉浪费和花粉竞争以探究传粉策略和植物繁殖策略。这些努力将为双翅目传粉昆虫的知识普及、资源保护与利用研究等方面提供参考。     

枣树访花昆虫多样性及药剂的影响

为了解枣树花期的访花昆虫,更好地利用昆虫为其授粉,本文对山西运城市临猗县、晋中市太谷县和吕梁市临县3地枣树的访花昆虫进行了调查,结果表明:枣树访花昆虫共计23种,隶属4目12科。运城临猗与晋中太谷间群落相似性最高,相似性系数为0.27,属于中等不相似,其它为极不相似。日活动规律观察表明,膜翅目与双翅目都属于单峰型,活动高峰为9∶30-10∶00、7∶30-8∶00。同一生境下,喷施药剂会影响访花昆虫的数量,一天中喷施清水的枣树访花昆虫244头,喷施药剂的枣树访花昆虫仅61头。     

Diversity and host associations of dipteran insects exploiting fungal fruiting bodies in Hokuriku,central Japan

To clarify the diversity and host associations of dipteran insects exploiting fungal fruiting bodies, we collected fruiting bodies at 18 localities in Hokuriku region, central Japan, from 2012 to 2015 and examined them for the emergence of insects. In total, 14,107 dipteran individuals belonging to 20 families emerged from fungi of 8 orders, 25 families, 49 genera and 129 species. Approximately 79% of dipteran individuals belonged to three families, Phoridae, Muscidae and Drosophilidae. The faunal similarity at the family level was relatively high between central (warm‐temperate) and northern (cool‐temperate) areas of Japan. However, the species composition of Drosophilidae was much different between central and northern Japan. The difference in the species composition was discussed in relation to the climatic conditions and fungal flora. None of the species from Drosophilidae, Phoridae, Muscidae, Mycetophilidae, Lonchaeidae and Chloropidae were specialists (they exploited more than one species of fungi), but they showed differences their fungi preference. Adults of some families, especially Drosophilidae, were frequently collected from fruiting bodies, but those of other families were seldom collected, probably reflecting differences in adult feeding ecology.     

The forgotten flies: the importance of non-syrphid Diptera as pollinators

Bees, hoverflies and butterflies are taxa frequently studied as pollinators in agricultural and conservation contexts. Although there are many records of non-syrphid Diptera visiting flowers, they are generally not regarded as important pollinators. We use data from 30 pollen-transport networks and 71 pollinator-visitation networks to compare the importance of various flower-visiting taxa as pollen-vectors. We specifically compare non-syrphid Diptera and Syrphidae to determine whether neglect of the former in the literature is justified. We found no significant difference in pollen-loads between the syrphid and non-syrphid Diptera. Moreover, there was no significant difference in the level of specialization between the two groups in the pollen-transport networks, though the Syrphidae had significantly greater visitation evenness. Flower visitation data from 33 farms showed that non-syrphid Diptera made up the majority of the flower-visiting Diptera in the agricultural studies (on average 82% abundance and 73% species richness), and we estimate that non-syrphid Diptera carry 84% of total pollen carried by farmland Diptera. As important pollinators, such as bees, have suffered serious declines, it would be prudent to improve our understanding of the role of non-syrphid Diptera as pollinators.     

Phenology and flower-visiting entomofauna of six species of Lindera (Lauraceae) in Japan

In this study we investigated floral biology and flower-visiting insect fauna in natural populations of six dioecious species of Lindera (Lauraceae) in Kyoto, Japan. Flowers of the Lindera species were similar in structure and floral attractants, and were visited by a wide range of insects. Although typical of generalist-pollinated flowers, interspecific differences were found in flower-visitor composition. All species of Lindera flowered early in the growing season, from February to May. However, peak flowering periods of different species of Lindera were staggered. Slight interspecific and intersexual divergence of flowering phenologies may reduce interspecific cross-pollination. Results of this study suggest that interspecific segregation of pollinators was associated with seasonal divergence of phenological patterns, rather than character displacement of floral attractants.     

Pollen and gene flow in fragmented habitats

Abstract. Habitat fragmentation affects both plants and pollinators. Habitat fragmentation leads to changes in species richness, population number and size, density, and shape, thus to changes in the spatial arrangement of flowers. These changes influence the amount of food for flower-visiting insects and the quantity and quality of pollinations. Seed set in small populations is often reduced and genetic variation is expected but not always found to be low. The majority of studies show that low flower densities have reduced pollination success and higher inbreeding. Density effects are stronger than size effects. Most studies concluded that species richness in flower-visiting insects is directly related to richness in plant species. However, the consequences of low insect species richness for pollination are not always clear, depending on the studied pollinator-plant relationship. The effects of the presence of simultaneously flowering species are highly dependent on the circumstances and may range from competition to facilitation. Other flowering plant species may play a role as stepping stones or corridor in the connection between populations. In the absence of stepping stones even short distances between populations act as strong barriers for gene flow. We illustrate the present review paper with own data collected for three plant species, rare in The Netherlands: Phyteuma spicatum ssp. nigrum (Campanulaceae), Salvia pratensis (Labiatae) and Scabiosa columbaria (Dipsacaceae). The species differ in their breeding systems and in the assemblage of visitor species. Data are shown on the effects of population size on species richness with consequences for seed set. Effects of flower density and isolation on pollen exchange are given. Since plant reproduction depends on the behaviour of individual insects and not on the overall behaviour of the species, the examples all point to individual insects and extrapolate to effects at the species level.