Effects of Aphis fabae Scop, and of its attendant ants and insect predators on yields of field beans (Vicia faba L.)

Predators (mainly coccinellid adults and larvae and syrphid larvae), although few, were important in decreasing numbers of Aphis fabae on a small plot of field beans during the early stages of infestation in a year favourable to the aphid. At the same time, ants (Lasius niger L.), attending aphids on other plants on the same plot, effectively protected the aphids from predators for about 2 weeks, enabling the attended aphids to multiply faster than the unattended. When all aphid populations started to decline, predators became more numerous and accelerated the decline on both sets of plants. Bean plants without aphids yielded fifty-six seeds per plant; those with aphids but free from ants gave seventeen; and those with ant-attended aphids, eight seeds per plant. The damage and loss of yield was caused by the large aphid populations that developed when the pods were maturing, and not by the fewer aphids present when the plants were in flower. It appears that small, temporary infestations during flowering might increase the yield of field beans.     

EFFECTS OF POLLINATION TIMING ON FRUITING IN ASCLEPIAS SPECIOSA TORR. (ASCLEPIADACEAE)

A series of hand-pollination experiments was performed to test the hypothesis that pollination timing determines which flowers produce pods in Asclepias speciosa, a species with few ovaries maturing into fruit. A comparison of fruiting of different aged ovaries showed that throughout anthesis, pistils are equally receptive to pollen tube penetration and growth. Pollen declines in vigor as flowers age as indicated by comparisons of different aged pollen both in vitro and in vivo. However, the overall effect of this decline on fruiting in the field is lessened by a simultaneous decline during anthesis in the rate of pollinium removal by insect pollinators. Within an umbel, earlier pollinated flowers are more likely to form mature pods than flowers pollinated 2 days later, apparently as a result of within umbel competition between developing pods for limited resources. The longer the delay between pollinations within umbels, the more mature pods form, probably as a result of a decline in intensity of competition between pods. Pollinations during the afternoon result in fewer mature pods and seeds than morning and evening pollinations, although fruiting is not dependent on humidity or temperature at the time of pollination. Differences in mature pod production between treatments were not significant for any experiment indicating that ecological or evolutionary factors other than pollination timing have the greatest effect on fruiting.     

A supplementary contribution of ants in the pollination of an orchid, Epipactis thunbergii, usually pollinated by hover flies

It has been controversial how extensively ants contribute to pollination, and we evaluated the contribution of the Japanese carpenter ant, Camponotus japonicus, to the pollination of an orchid, Epipactis thunbergii. Two-year field studies revealed that (1) the ant workers foraged even in cool/cloudy conditions and accordingly visited orchid flowers more frequently (about 40% of all the visitors) than hover flies, the principle pollinators (10–20%), and that (2) the flower-visiting ants occasionally removed pollinia from the anther and then delivered pollen onto the stigmatic surface of other flowers, although self-pollination might frequently occur in the consecutive visits of flowers within an inflorescence. An artificial pollination experiment with pollinia which had been transferred to the ant integument showed that (3) the treated flowers produced as many fruits and seeds as control flowers. We concluded that C. japonicus workers could actually pollinate E. thunbergii flowers and their relative importance as pollinators appeared to be largely dependent on the abundance of flower-visiting workers or weather conditions during the flowering period, which mainly determined the availability of hover flies.     

Selection of plant parts by Depressaria multifidae (Lep., Oecophoridae) on its seasonally-restricted hostplant, Lomatium grayi (Umbelliferae)

ABSTRACT.

• 1 Depressaria multifidae Clarke feeds on a broader variety of Umbelliferae plant parts than other Depressaria species.
• 2 Early instar larvae feed in the sheaths surrounding floral buds and leaves. Later instar larvae feed in the sheaths and floral stems and on flowers and leaves.
• 3 Floral stems bored by larvae had significantly larger basal stem diameters than floral stems that were not bored. Smaller stems usually have umbels with only male flowers, and wither after flowering, too soon for larvae to complete development. In contrast, larger stems often have umbels with some hermaphroditic flowers, which remain green and erect long enough for larvae to complete development. Hence, selection may favour larvae that bore only in relatively large stems.
• 4 In the laboratory, larvae fed sheaths with enclosed floral buds, flowers, or leaves all pupated at the same weight, but larvae fed floral stems pupated at a significantly lower weight. Larval and pupal development time was the same on all plant parts.
• 5 In the field, larvae restricted to a single umbel throughout development pupated at the same weight as those restricted to a single leaf.
• 6 Unlike in other Depressaria species, nitrogen levels only partly correspond to the pattern of use of plant parts in D.multifidae. Nitrogen values varied as follows: floral buds > immature leaves ≥ flowers > floral stalks > sheaths excluding floral buds or leaves.
• 7 The broad variety of plant parts used by D.multifidae may result partly from the problem of feeding on a small, seasonally restricted hostplant; the greater use of sheaths and floral stems than in other Depressaria species may result from selection for safety from parasites or predators.
• 8 The results for D.multifidae indicate that the way in which an insect feeds on a plant species can vary broadly even at a single site.

     

Interaction between flowers, ants and pollinators: additional evidence for floral repellence against ants

It has been commonly suggested that ants negatively affect plant pollination, particularly in the tropics. We studied ant–flower–pollinator interactions in a lowland rainforest in Borneo. Frequency and duration of pollinator visits were compared between flowers attended by ants and flowers from which ants were excluded. In all four plant species studied, the activity of ants decreased the rate and/or duration of the pollinators’ floral visits. For this and other reasons it is expected that plants repel ants from flowers during anthesis. We tested this prediction for a different set of plant species in which we observed the behaviour of Dolichoderus thoracicus ants when encountering flowers. In eight out of 18 plant species studied, ants showed a significantly higher rejection rate when they encountered flowers than when they encountered controls. Our results are thus consistent with the hypothesis that ants may negatively affect plant fitness by reduced intensity of pollinator visits and that ants are repelled from flowers of many tropical plant species, although this repellence is clearly not ubiquitous.     

Ant attendance in aphids: why different degrees of myrmecophily?

1. Aphids show a range of associations with ants from nonattendance to obligate myrmecophily. Aphis fabae cirsiiacanthoides is facultatively associated with ants, while Symydobius oblongus is an obligate myrmecophile. The selection pressures that have shaped these associations are unknown. 2. The consequences for these aphids of their different degrees of associations with ants were determined, in terms of costs and benefits to individuals and colonies in laboratory and field experiments. In the laboratory, individuals of A. f. cirsiiacanthoides performed worse and those of Symydobius oblongus performed better when attended by the ant Lasius niger than when unattended. For example, when ant-attended, A. f. cirsiiacanthoides developed more slowly, were smaller, and invested less in gonads, whereas S. oblongus developed more quickly, were larger, and invested more in gonads. In addition, the ant regulated the population size of S. oblongus to an average of 50–70 individuals per birch sapling by removing aphids, but did not regulate the population size of A. f. cirsiiacanthoides. 3. Under field conditions, ant-attended colonies of both A. f. cirsiiacanthoides and S. oblongus achieved higher peak numbers and lasted longer, and ant-attended colonies of A. f. cirsiiacanthoides produced more alate dispersers than unattended colonies. 4. The implications of divergent selection pressures for the development of myrmecophily in aphids are discussed.     

Mating Strategies in Solitary Aphid Parasitoids: Effect of Patch Residence Time and Ant Attendance

Mate finding and dispersal from the natal patch in parasitoid Hymenoptera are influenced by the availability of host resources and interactions with other organisms. We compared the mating behavior of three solitary aphid parasitoids, Aphidius ervi Haliday, Lysiphlebus hirticornis Mackauer and Pauesia pini (Haliday) (Hymenoptera: Braconidae: Aphidiinae) that differ in host resource exploitation and ant mutualism. In L. hirticornis, which is obligately ant-attended, the residence time on the natal patch was approximately 4 h compared with less than 2 h in the facultatively ant-attended P. pini; the sexes did not differ in residence time. Females of A. ervi, which is not attended by ants, stayed for slightly more than 2 h on the natal patch while their male siblings remained for only 1 h. In L. hirticornis, 90% of all siblings in a clutch mated on the natal patch but only 13% in A. ervi and 42% in P. pini did so. Off-patch matings (23%) were observed only in A. ervi. Males and females of L. hirticornis were 12-times more likely to mate on the natal patch when aphids and ants were present than when either of the latter species was removed; and patch residence time declined from approximately 4 h to approximately 2.5 h in the absence of either aphids or ants. We propose that, in aphidiine wasps and perhaps other quasigregarious parasitoids, mating behavior is influenced by the availability of resources on the natal patch and the presence or absence of trophobiotic ants. Partial sib mating is expected in species producing large clutches and having a long patch residence time.     

Reproductive biology and reproductive output assessment in natural and introduced subpopulations of Apium bermejoi,a ‘Critically Endangered’ endemic plant from Menorca (western Mediterranean)

Apium bermejoi is a critically endangered species that is native to Menorca, an island of 702 km² located in the western Mediterranean basin. We investigated the reproductive biology of this species and evaluated flowering/fruiting phenology and reproductive output in wild subpopulations over four years (2007–2010). We used ex situ cultivated plants to study floral biology and performed bagging experiments to elucidate the breeding system. We addressed the role of ants in seed dispersal/predation in wild subpopulations by analysing the presence of A. bermejoi seeds in the waste accumulated on the refuse piles of all anthills. Our observations indicated that flowers are protandrous but that there is no dichogamy between flowers within and among umbels of the same individual. Moreover, individuals are mixed in the field because the close germination of several seeds and the plant’s caespitose habit promote cross‐pollination. Bagging experiments demonstrated that the species is autogamous, and seeds from selfing (bagged with muslin) showed high final germination (>80%). However, the fruit set of selfed umbels (0.3–0.4 per 1) was lower than that of open‐pollinated umbels (0.6–0.8 per 1), and the high pollen/ovule (P/O) ratio (3641±133, n= 30) was also indicative of xenogamy. Plants bagged with muslin, bagged with tulle or barred from contact from ants exhibited similar fruit sets, lower than those observed in isolated and control groups, suggesting that anemophily and pollination by flying insects were less effective than ant‐based pollination. We identified eight species of floral visitors, and we noted that ants were the most frequent visitors. Although we found some A. bermejoi seeds in the refuse piles of Messor bouvieri anthills, most of the seeds were not damaged (99.1%), and the number of seeds found represents only a small proportion of the overall fruit production. Because sexual reproduction is the main reproductive mechanism of these plants, despite their high potential for space colonisation and vegetative propagation, the reproductive output for each year determines the subpopulation configuration in the following year.     

Predator and parasitoid attacking ant-attended aphids: effects of predator presence and attending ant species on emerging parasitoid numbers

Interaction between a predator and a parasitoid attacking ant-attended aphids was examined in a system on photinia plants, consisting of the aphid Aphis spiraecola, the two ants Lasius japonicus and Pristomyrmex pungens, the predatory ladybird beetle Scymnus posticalis, and the parasitoid wasp Lysiphlebus japonicus. The ladybird larvae are densely covered with waxy secretion and are never attacked by attending ants. The parasitoid females are often attacked by ants, but successfully oviposit by avoiding ants. The two ants differ in aggressiveness towards aphid enemies. Impacts of the predator larvae and attending ant species on the number of parasitoid adults emerging from mummies per aphid colony were assessed by manipulating the presence of the predator in introduced aphid colonies attended by either ant. The experiment showed a significant negative impact of the predator on emerging parasitoid numbers. This is due to consumption of healthy aphids by the predator and its predation on parasitized aphids containing the parasitoid larvae (intraguild predation). Additionally, attending ant species significantly affected emerging parasitoid numbers, with more parasitoids in P. pungens-attended colonies. This results from the lower extent of interference with parasitoid oviposition by the less aggressive P. pungens. Furthermore, the predator reduced emerging parasitoid numbers more when P. pungens attended aphids. This may be ascribed to larger numbers of the predator and the resulting higher levels of predation on unparasitized and parasitized aphids in P. pungens-attended colonies. In conclusion, a negative effect of the predator on the parasitoid occurs in ant-attended aphid colonies, and the intensity of the interaction is affected by ant species.     

VARIATION IN THE POLLINARIA,ANTHERS, AND ALAR FISSURES OF COMMON MILKWEED (ASCLEPIAS SYRIACA L.)

We measured 10 characters of pollinaria, anthers, and alar fissures from the flowers of seven clones of common milkweed Asclepias syriaca L. to test whether significant differences existed among them. Strong among-clone differences existed for most of these characters. However, these differences were not correlated with each other, except for width of the alar fissure and width of the translator arm. Thus, these floral structures vary mostly in shape, rather than size per se. Few correlations among characters occurred at a within-clone level. Clones growing in the open and shade differed in half of the characters measured, but habitat did not substantially change the among-clone size patterns observed. The alar fissure–translator arm relationship might promote differential uptake of pollinia; however, A. syriaca does not exhibit a clear separation into donor and recipient clones.     

The turnover of milkweed pollinia on bumble bees,and implications for outcrossing

Summary Bumble bees (Bombus spp.) picked up a pollen packet (pollinium) of milkweed (Asclepias syriaca L.) every 2–5 h, usually more rapidly on their feet than on their mouthparts. Pollinia were retained an average of slightly over one day on the mouthparts and one-quarter day on the feet. This long retention period enhances the possibility of outcrossing in this largely or completely self-incompatible species. Although many more pollinia were carried on the feet, the longer retention of those on the mouthparts resulted in their collective outcrossing potential exceeding that of pollinia on the feet. Once pollinia became attached to the bees (via their attachment mechanisms, the corpuscula), others often attached to the translator arms (connecting corpusculum with pollinia) of the first pollinia. Long strings of pollinia and corpuscula often resulted, but they frequently were shed down to a single corpusculum, which was usually retained for long periods (estimated retention time=12–43 days). During the middle and latter part of the flowering period about two-thirds of the bees' feet carried only a single corpusculum. Feet in this condition picked up extremely few pollinia and thus were largely unavailable as sites for pollen transfer. Having several single corpuscula on the feet greatly lowered the number of pollinia carried by a bee over the season. Single corpuscula occurred much less frequently on the mouthparts and were shed over 25 times as rapidly as those on the feet. Many more bumble bees moved between clones than did other possible diurnal pollinators, largely a result of being several times more abundant than all other visitors combined. This factor, plus their heavy pollinia load, suggests that they were the most important diurnal pollinators of these clones.     

Oviposition preferences of Maculinea alcon as influenced by aphid (Aphis gentianae) and fungal (Puccinia gentianae) infestation of larval host plants

Abstract 1. The influence of infestation of the larval host plant Gentiana cruciata on the egg‐laying preferences of the xerophilous ecotype of Alcon Blue butterfly (Maculinea alcon) was studied in a semi‐dry grassland area (Aggtelek Karst Region, Northern Hungary). 2. We examined whether oviposition patterns of females differed when G. cruciata stems were uninfested compared with when they were infested by an aphid (Aphis gentianae) or a rust (Puccinia gentianae) species. 3. Females laid more than 90% of their eggs on fertile, uninfested G. cruciata stems, although these stems comprised only ～ 50% of the total stems available. Stems infested by aphids were similar to uninfested ones in properties that had a strong correlation with egg numbers, and yet there were significantly fewer eggs on infested stems than on intact ones. 4. Females never laid eggs on parts of Gentiana stems infested by aphids, and the presence of Lasius paralienus ants, which have a mutualistic interaction with Aphis gentianae, did not increase the repulsive effect of aphids. Infection of Gentiana by Puccinia did not influence the egg‐laying behaviour of females, even though the flowers and buds of infested stems exhibited a delayed development. 5. Aphid infestation can influence butterfly oviposition patterns through both direct and indirect effects. The presence of aphids directly excluded oviposition, but our data also indicated the possibility of an indirect effect of aphid infestation. Stems that had no aphids at the last egg counting, but were infested prior to it, had significantly fewer eggs than those that were never infested.     

Pollen viability reduction as a potential cost of ant association for Acacia constricta (Fabaceae)

Field studies investigating the impact of ants on the reproduction of plants bearing extrafloral nectaries have traditionally focused on seed production, a component of female fitness. The purpose of this study was to test whether ants can affect the pollen viability, a component of male fitness, when they visit flowers of the shrub Acacia constricta. Acacia constricta inflorescences hand-pollinated with flowers over which Formica perpilosa ants had crawled set significantly fewer seed pods than inflorescences hand-pollinated by control flowers that had no contact with ants. Many ant species secrete antibiotic substances onto the integument that render pollen inviable, and these secretions are probably the mechanism for reduced pollen viability in this study. The ratio of seed pods produced by self-pollinated inflorescences to those produced by cross-pollinated inflorescences was 0.16, indicating that A. constricta is largely self-incompatible. Because F. perpilosa workers forage primarily on the acacia tree under which they nest, they are unlikely to serve as efficient vectors of outcrossing. Previous work showed that A. constricta shrubs with F. perpilosa ants produce approximately twice as many seeds as similarly sized plants not so associated. The results indicate that association with F. perpilosa could cause a reproductive trade-off for A. constricta: benefits to female function may be accompanied by costs to male function. Selection to discourage ant visitation to flowers may have affected the pollination biology of this and other ant-associated plant species.     

Costs and benefits of ant attendance to the drepanosiphid aphid Tuberculatus quercicola

The defensive effects of ants against aphid predators have been well documented in the mutualistic relationship of aphids and their attending ants. However, it is not clear whether ant attendance has any direct effect on the aphids' growth and reproduction. Through field experiments, this study evaluates the benefits and, in particular, the costs of ant attendance to aphid colonies, focusing on the drepanosiphid aphid Tuberculatus quercicola which is associated with the Daimyo oak, Quercus dentata , and which is always attended by the red wood ant Formica yessensis . Ant attendance was clearly beneficial to the aphid; the exclusion of ants led to a significant increase in the extinction rate of aphid colonies. However, MANOVA and randomized block ANOVA indicated that in colonies continuously attended by ants, aphids had significantly smaller body size and produced a smaller number of embryos than in colonies isolated from ants when they were reared under homogeneous host conditions free from natural enemies. Thus, ant attendance had a negative influence on the growth and reproduction of the aphids, even though it contributed to the greater longevity of the aphid colonies. We hypothesize that ant-attended aphids are under intense selective pressures that act against aphid clones which fail to attract many ants, so that aphids have developed an adaptive mechanism to allocate a larger fraction of resources to the honeydew when they are requested to do so by the ants in order to ensure the ants' consistent visitation.     

雄全同株植物簇花芹花期性别分配与开花式样

簇花芹(Soranthus meyeri)是古尔班通古特沙漠中常见的、具雄全同株性系统的伞形科多年生早春短命植物。该文对簇花芹花期性比(两性花数/总花数)与植株大小的关系及其开花式样进行了研究, 重点对花期大小依赖的性别资源分配进行了讨论。结果表明: 2006-2008年簇花芹群体水平的性比分别为0.69 ± 0.03、0.62 ± 0.03和0.69 ± 0.02, 彼此间无显著差异( p > 0.05), 表明其性比是相对稳定的, 可能受遗传因素的控制。雄花生物量与花粉量均比两性花的小, 说明产生雄花比产生两性花所需资源少。一级复伞形花序比二级复伞形花序具有较多的两性花, 说明前者易从植株上获得资源用于增加雌性适合度; 而后者产生较多的雄花以避免在雌性功能上资源投入的浪费, 增大花展示以吸引更多传粉者来增加花粉输出总量, 提高其整体适合度。植株水平的性比与地上营养器官的生物量间呈正相关关系, 说明较大个体对雌性功能的投资较大, 雌性繁殖成功受资源限制。复伞形花序内各伞形花序几乎同时向心开放, 且所有两性花及花序均为雄性先熟, 雌雄阶段完全分离, 但一级复伞形花序比二级复伞形花序早开放约5天, 彼此开花重叠期约为1天。这些特征对于一级复伞形花序进行异株异花授粉以及植株内不同级别花序间的同株异花传粉、避免雌雄功能间的干扰具有重要意义。     

Injury to oilseed rape caused by mirid bugs (Lygus) (Heteroptera: Miridae) and its effect on seed production

Injury by Lygus spp. to oilseed rape, Brassica napus L. and Brassica campestris L., was assessed based on laboratory and field studies in Alberta, Canada. The visible injuries consisted of lesions on the surfaces of stems, buds, flowers and pods similar to those described for other crops. They caused buds and flowers to abscise and seeds to collapse, and reduced the weight of healthy seeds produced per pod. The plants compensated for bud loss so that no net reduction in the number of pods occurred. However, in some situations the damage to buds resulted in a reduced seed yield that increased with the amount of injury. The plants also compensated for flower loss so that no net reduction in the number of pods occurred, but seed yield declined as injury increased. Plants did not compensate for seeds that collapsed as a result of lygus feeding. The feeding activity of lygus bugs reduced seed yield in oilseed rape.     

The aphid-tending ant Lasius fuji exhibits reduced aggression toward aphids marked with ant cuticular hydrocarbons

Some aphid species are attended by ants, which protect aphids against enemies, but ants sometimes prey on the aphids they are attending depending on the resource conditions. A previous study indicated that the ant Lasius niger preys less on the aphid individuals that experienced ant attendance than on those that did not. This observation leads to the hypothesis that ants transfer some substances to the aphids they attend and selectively prey on the aphids without the substances. In this study, we focus on cuticular hydrocarbons (CHCs), which are used by ants as nestmate recognition substances, and test whether ants discriminate the aphids on the basis of CHCs. We confirmed that the ant Lasius fuji preyed less on the aphids that were attended by their nestmates than those that were not attended. Glass dummies treated with CHCs from attended aphids were attacked less by ants than those treated with CHCs from non-attended aphids. The CHC profiles of ant attended aphids resembled those of the ants, suggesting that ants’ CHCs are transferred to the aphids’ body surface through ant attendance. These results support the hypothesis that ants “mark” their attended aphids with their CHCs and the CHCs reduce ant predation intensity.     

Combined effects of inflorescence architecture, display size, plant density and empty flowers on bumble bee behaviour: experimental study with artificial inflorescences

Pollen dispersal by pollinators is governed by the extent to which diverse effects on pollinator behaviour act independently or augment or moderate each other. Using artificial inflorescences, we assessed the behavioural responses of bumble bees to inflorescence architecture (raceme, panicle, and umbel), inflorescence size (7 or 13 flowers), inter-inflorescence distance and the proportion of empty flowers per inflorescence. The advantage of large inflorescences in terms of attractiveness was larger for racemes and umbels than for panicles, whereas the effect of inter-inflorescence distance on the number of successive probes was smaller for racemes than for panicles and umbels. The number of flowers probed per visit increased almost proportionally with display size when fewer flowers were empty, whereas the number increased less when many flowers were empty. Our results suggest that display size and the spatial arrangement of flowers and nectar within inflorescences can contribute to efficient pollination by affecting pollinator behaviour interactively.     

Honey bees are the dominant diurnal pollinator of native milkweed in a large urban park

In eastern North America, the field milkweed, Asclepias syriaca L. (Asclepiadaceae), is used in planting schemes to promote biodiversity conservation for numerous insects including the endangered monarch butterfly, Danaus plexippus (Linnaeus) (Nymphalidae). Less is known about its pollinators, and especially in urban habitats where it is planted often despite being under increasing pressure from invasive plant species, such as the related milkweed, the dog‐strangling vine (DSV), Vincetoxicum rossicum (Kleopow) Barbar. (Asclepiadaceae). During the A. syriaca flowering period in July 2016, we surveyed bees in open habitats along a DSV invasion gradient and inspected 433 individuals of 25 bee species in 12 genera for pollinia: these were affixed to bees that visited A. syriaca for nectar and contain pollen packets that are vectored (e.g., transferred) between flowers. Of all bees sampled, pollinia were found only on the nonindigenous honeybee, Apis mellifera (43% of all bees identified), as well as one individual bumblebee, Bombus impatiens Cresson. Pollinia were recorded from 45.2% of all honeybees collected. We found no relationship between biomass of DSV and biomass of A. syriaca per site. There was a significant positive correlation between A. syriaca biomass and the number of pollinia, and the proportion vectored. No relationship with DSV biomass was detected for the number of pollinia collected by bees but the proportion of vectored pollinia declined with increasing DSV biomass. Although we find no evidence of DSV flowers attracting potential pollinators away from A. syriaca and other flowering plants, the impacts on native plant–pollinator mutualisms relate to its ability to outcompete native plants. As wild bees do not appear to visit DSV flowers, it could be altering the landscape to one which honeybees are more tolerant than native wild bees.