High floral resource density leads to neural constraint in the generalist,floriphilic katydid,Phaneroptera brevis (Orthoptera: Phaneropterinae)

1. The neural constraint hypothesis has been investigated in the field of insect–plant interactions. It predicts that the consumer's detection ability, time spent on resources, and efficiency in resource use are affected by different aspects of resource availability. 2. The applicability of this hypothesis in florivory, however, generally lacks a mechanistic understanding of the effect of resource density on neural constraint, so using caged experiments, the (i) ability of a generalist, floriphilic katydid [(Phaneroptera brevis (Serville)] to find a floral resource (inflorescences of Bidens pilosa L.), (ii) attentiveness of the katydid on this resource after successfully detecting the floral resource, and (iii) efficiency of resource use under varying densities of the floral resource were studied. 3. The present results indicated no evidence of an obvious effect of floral resource density on the detection of resources by the florivore but an increase in floral‐resource density generally led to lower efficiency and attentiveness in the foraging katydids. 4. These findings provide the first evidence of the neural constraint hypothesis in the context of resource density and corroborate the applicability of the neural constraint hypothesis in florivory.     

Florivory by a floriphilic katydid,Phaneroptera brevis,induces changes in a leaf trait in Lantana camara

1. Plants can induce a response when they are attacked by herbivores. Although the induction of responses by herbivory in both flowers and leaves is relatively well studied, whether florivory (feeding of flowers) can also induce responses in flowers and leaves is less well explored and there are still unanswered questions. These include whether plants exhibit different levels of induced responses depending on the length of exposure to the florivores. 2. To address this knowledge gap, this study used a tropical floriphilic katydid, Phaneroptera brevis, and its non‐native food plant, Lantana camara. Nursery experiments were performed in which dry matter content and anthocyanin concentration of the flower (corolla and stamens), leaf dry matter content, and leaf blade punch resistance were measured at three time phases before and after exposing the plant to the katydid individuals for 0–7 days. 3. It was demonstrated that increasing the length (days) of exposure to the katydid individual leads to higher levels of induced plant response (leaf blade punch resistance), but only in the leaves. It was also shown that higher levels of induced plant response owing to the increase in the length of exposure to the katydid individual was not observed beyond the first set of leaves developed after the exposure. 4. These results address the knowledge gap and show that plants can exhibit different levels of induced responses depending on the length of exposure to florivores. This study thus highlights the far‐reaching importance of florivory on plants.     

Individual‐ and population‐level personalities in a floriphilic katydid

Behaviour, including personality, informs us about the response of animals towards their changing environment. Despite the widespread occurrence of florivorous insects and the important but often underrated ecological roles that they play, the study of florivore behaviour is neglected relative to that of pollinators and other herbivores. Specifically, we do not know how different personality types can develop among florivores and enable them to persist in habitats with an ephemeral and dynamic availability of food resources. To address this knowledge gap, we investigated the following questions: whether the (a) inter‐individual differences of exploration and boldness are consistent; (b) inter‐population differences of exploration and boldness are consistent; (c) exploration and boldness are correlated. We collected individuals of the polyphagous floriphilic katydid, Phaneroptera brevis from four populations from wasteland sites in Singapore and performed a personality assay conducted in an insectary to investigate the exploratory and boldness levels of the individuals and populations. The major novel finding was that the floriphilic P. brevis katydids exhibit population‐level personality types for boldness, but not for exploration. Some katydid individuals were consistently more exploratory and bolder than other individuals. However, contrary to our predictions, we did not find any evidence of behavioural syndromes in the katydid individuals, as the boldness level for individuals was not significantly correlated with exploration for individuals. This suggests that an individual which is more exploratory may not be equally keen to take risks and consume novel food that it encounters. Our findings also suggest that boldness and exploration are linked to ecologically important behaviours, but more studies are needed to better understand population‐level personality and how and why natural selection may favour the evolution of personality in certain populations.     

Florivory indirectly decreases the plant reproductive output through changes in pollinator attraction

Species often interact indirectly with each other via their traits. There is increasing appreciation of trait‐mediated indirect effects linking multiple interactions. Flowers interact with both pollinators and floral herbivores, and the flower‐pollinator interaction may be modified by indirect effects of floral herbivores (i.e., florivores) on flower traits such as flower size attracting pollinators. To explore whether flower size affects the flower‐pollinator interaction, we used Eurya japonica flowers. We examined whether artificial florivory decreased fruit and seed production, and also whether flower size affected florivory and the number of floral visitors. The petal removal treatment (i.e., artificial florivory) showed approximately 50% reduction in both fruit and seed set in natural pollination but not in artificial pollination. Furthermore, flower size increased the number of floral visitors, although it did not affect the frequency of florivory. Our results demonstrate that petal removal indirectly decreased 75% of female reproductive output via decreased flower visits by pollinators and that flower size mediated indirect interactions between florivory and floral visitors.     

Specialisation in prey capture drives coexistence among sympatric spider‐hunting wasps

1. Sister taxa that coexist in the same space and time often face competition due to the use of similar resources. However, some closely related species can adopt fine‐grained specialisation in resource use to coexist. This study investigated niche overlap between three sympatric spider‐hunting wasp species of the genus Trypoxylon (Hymenoptera: Crabronidae) known to nest in three of the habitats found in the study area. 2. First, the co‐occurrence of these wasp species in the three habitats was estimated, as a proxy for potential competition. Then, the following hypotheses were tested: (i) niche partitioning is seen more often between species that co‐occur in a habitat, whereas there is niche overlap between species nesting in distinct habitats (prey specialisation hypothesis); and (ii) wasp species capture prey according to their size (physical constraint hypothesis). 3. Two pairs of wasp species were found consistently nesting in the same habitat. Niche partitioning based on prey taxa occurred regardless of the habitat preference. It was also found that differences in the size of wasps reflected distinctions in the size of their prey. 4. These findings were consistent over the years, showing that the significance of specialisation in foraging activities and physical constraints during prey capture can play key roles in the coexistence of sympatric species. The distinctions in the foraging strategies of these wasps are discussed, as well as potential mechanisms driving the evolution in prey specialisation, with insights for future studies.     

Preference induction and the benefits of floral resources for a facultative florivore

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Florivory: the intersection of pollination and herbivory

Plants interact with many visitors who consume a variety of plant tissues. While the consequences of herbivory to leaves and shoots are well known, the implications of florivory, the consumption of flowers prior to seed coat formation, have received less attention. Herbivory and florivory can yield different plant, population and community outcomes; thus, it is critical to distinguish between these two types of consumption. Here, we consider the ecological and evolutionary consequences of florivory. A growing number of studies recognize that florivory is common in natural systems and in some cases surpasses leaf herbivory in magnitude and impact. Florivores can affect male and female plant fitness via direct trophic effects and through altered pathways of species interactions. In particular, florivory can affect pollination and have consequences for plant mating and floral sexual system evolution. Plants are not defenceless against florivore damage. Concepts of resistance and tolerance can be applied to plant–florivore interactions. Moreover, extant theories of plant chemical defence, including optimal defence theory, growth rate hypothesis and growth differentiation–balance hypothesis, can be used to make testable predictions about when and how plants should defend flowers against florivores. The majority of the predictions remain untested, but they provide a theoretical foundation on which to base future experiments. The approaches to studying florivory that we outline may yield novel insights into floral and defence traits not illuminated by studies of pollination or herbivory alone.     

Uncovering different parameters influencing florivory in a specialist herbivore

1. It has become increasingly recognised that several herbivores switch from folivory (leaf‐feeding) to florivory (flower‐feeding) during larval development. Yet, it remains poorly understood which cues influence this behaviour, whether a switch to florivory is consistently shown on different hosts, and to what extent florivory could be hindered by plant traits. 2. Using the sawfly Athalia rosae and two Brassicaceae differing in architecture and surface structure, the cues that influence larval movement to the flowers were investigated. A broad set of behavioural assays was employed and physical and chemical plant traits potentially affecting the larvae were analysed. Furthermore, the consequences of folivory versus florivory on insect performance were studied. 3. The larvae preferred flowers over leaves. Consumption of particular flower parts correlated partly with measured plant traits such as glucosinolate distribution. Visual cues were of higher importance than volatile cues. The initial position of newly hatched larvae on plants influenced the probability of the larvae reaching the flowers during development. Trichomes and surface waxes hindered the larvae from moving upwards to the flowers. Larvae developed slower and gained less body mass when feeding on inflorescences of Brassica nigra than when feeding on leaves, in contrast to the patterns observed before on Sinapis alba, where florivory led to an improved performance. 4. This study demonstrates that florivory depends on various host plant traits. It reveals new insights into different parameters influencing this multifaceted phenomenon and into the expected impact on the ecology and fitness of both the attacking herbivores and the plants.     

Variation among individual butterflies along a generalist–specialist axis: no support for the 'neural constraint' hypothesis

Abstract 1. Degree of host specialisation was a continuous variable in a population of Edith’s checkerspot butterfly (Euphydryas editha). A novel host, Collinsia torreyi, had been added to the diet in response to anthropogenic disturbance, and then abandoned prior to the current study. Butterflies either showed no preference or preferred their traditional host, Pedicularis semibarbata. 2. Strength of preference for Pedicularis over Collinsia was measured in the field and used to estimate host specialisation of individual butterflies. Efficiency was estimated from the times taken by each insect to perform two tasks: (i) identification of a Pedicularis plant as a host, and (ii) successful initiation of oviposition after the decision to do so had been made. 3. There was no clear trend for association between host specialisation and either measure of efficiency. Generalists were not slower than specialists at identifying Pedicularis as a host or at handling it after deciding to oviposit. 4. Prior work indicated that generalists paid no detectable cost in terms of reduced discrimination among individuals of their preferred host species. 5. In contrast to other species, generalist E. editha paid in neither time nor accuracy. Why then does the diet not expand? Behavioural adaptations to the traditional host caused maladaptations to the novel host and generated short‐term constraints to evolutionary expansion of diet breadth. To date, however, no long‐term constraints have been found in this system. In those traits investigated to date, increased adaptation to the novel host has not caused reduced adaptation to the traditional host.     

Variation in floral morphology within a population of Aster hispidus var. tubulosus (Asteraceae,Astereae)

The family Asteraceae has a particular inflorescence, the capitulum, consisting of ray florets and disc florets. The ray florets function as petals that attract pollinators. Marked variation in the ray floret morphology is known in a natural population of Aster hispidus var. tubulosus (Asteraceae). We analyzed the variation and found two distinct types in the ray florets, the long tubular ray floret and the ligulate ray floret. In this species, therefore, the variation in floral morphology among capitula, each of which is the basic pollination unit, is caused by the variation in the composition of the two ray floret types among capitula. We evaluated the sources of the observed variation in the floral morphology among capitula within a population using a hierarchical analysis that separated within‐individual (i.e. among capitula within each individual) and between‐individual components of the variation. We found that the main source of the variation lay at the between‐individual level, not at the between‐capitulum level nested within individuals. This finding will provide the basic knowledge that enables future study exploring whether the between‐individual variation in floral morphology caused by the compositional variation of the ray floret types leads to differential pollination success of individual plants in species of Asteraceae.     

Ants and extrafloral nectaries: no evidence for plant protection in Helichrysum spp. — ant interactions

Summary Characterstics of Australian endemic Helichrysum bracteratum and H. viscosum suggest that foraging ants act as guards of developing flowerheads, protecting capitula from seed predators: (1) extrafloral nectar is secreted from leaves subtending the capitula and from bracts encircling the floral disc during pre- to post-flowering periods; (2) capitula are attended by ants; and, (3) encounters between ants and other capitula visitors, including predispersal seed predators such as Tephritis sp. (Diptera), can be frequent. In experiments to test the ant-guard hypothesis, exclusion of ants from plants increased abundance of other insects on the developing capitula. The difference between ant-access and ant-exclusion treatments was related to ant abundance on the access plants. These effects were statistically significant in spite of the large variation in insect activity between sites and through the season.The increased abundance of insects on capitula following ant-exclusion did not, however, result in significant increases in the number of adult seed predators observed on capitula, the number of immature seed predators in capitula, or capitula damage as estimated between ant-access and exclusion treatments of either H. bracteatum or H. viscosum. Further, the ant-exclusion treatment on H. bracteatum had no significant influence on pollination as measured by seed set or on the degree of parasitism of Tephritis sp. by Megastigmus sp. Site and season most strongly affected numbers of immature seed predators and damage to capitula.We discuss these findings in relation to the ant-guard hypothesis and suggest that generalization of the protection hypothesis to all plants with extrafloral nectaries is premature.     

Safflower susceptibility and response to feeding by grasshoppers

Feeding by three grasshopper species, Camnula pellucida, Melanoplus packardii and Melanoplus sanguinipes, on three safflower (Carthamus tinctorius) lines for a 6-wk period from anthesis was monitored under field conditions. Ratings of feeding damage to different plant parts (leaves, floral parts, capitula, and peduncles) and measurements after termination of feeding (dry weight, seed yield, seed weight, seeds per capitulum, and capitula per row) were compared among grasshopper species and safflower lines. The Melanoplus species fed preferentially on leaves, floral parts, and capitula, while C. pellucida exhibited only peduncle feeding, which resulted in head clipping. Defoliation of 20 to 30% was associated with significant increases in total dry matter, seed yield, and number of capitula. Further defoliation resulted in decreases. The safflower lines differed in response to grasshopper feeding. S-208 was most susceptible to defoliation by grasshopper feeding, exhibiting decreased dry weight, seed yield, and capitula number. Lesaf 34C-00 was most tolerant and only M. packardii caused significant dry weight and seed yield reductions. Feeding by C. pellucida on this line resulted in an overall seed yield increase. Feeding by M. sanguinipes on Seedtec-5 resulted in yield increases of up to 16%. It appears that certain grasshopper species can increase seed yield in some safflower lines by stimulating the production of additional capitula. Therefore, moderate populations of such grasshoppers in fields of appropriate safflower cultivars do not necessarily require control.     

Are breeding system and florivory associated with the abundance of Tillandsia species (Bromeliaceae)?

Plant species abundance is partly determined by reproductive success and the factors that limit this success. We studied the flowering phenology, breeding systems and florivory in a community of seven epiphytic Tillandsia spp. in a tropical dry forest in central Mexico. Flowering periods were distributed throughout the year, and corolla sizes suggested that most species share pollinators. The most common breeding system was self‐incompatibility (Tillandsia achyrostachys, T. caput‐medusae and T. hubertiana), T. lydiae was infertile, T. circinnatioides was partially self‐compatible and T. recurvata and T. schiedeana were self‐compatible with high autonomous self‐pollination. Floral morphology suggests that delayed selfing occurs in the autonomous self‐pollinated species, and separation between stigma and stamens could result in self‐pollination in the remaining species being avoided. Less than 5% of the inflorescences in the most abundant species (T. recurvata) suffered damage by florivores, but > 40% of inflorescences were damaged in the other species. In damaged inflorescences, fruit set decreased by up to 89%. Our data show that the dominant species (T. recurvata) is autogamous and its reproductive success is slightly reduced by resource constraints and florivory. In the less abundant species, resource limitation and florivory dramatically reduced reproductive success, but the strength of these limiting factors is season dependent. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 50–65.     

Short‐term prey field lability constrains individual specialisation in resource selection and foraging site fidelity in a marine predator

Spatio‐temporally stable prey distributions coupled with individual foraging site fidelity are predicted to favour individual resource specialisation. Conversely, predators coping with dynamic prey distributions should diversify their individual diet and/or shift foraging areas to increase net intake. We studied individual specialisation in Scopoli's shearwaters (Calonectris diomedea) from the highly dynamic Western Mediterranean, using daily prey distributions together with resource selection, site fidelity and trophic‐level analyses. As hypothesised, we found dietary diversification, low foraging site fidelity and almost no individual specialisation in resource selection. Crucially, shearwaters switched daily foraging tactics, selecting areas with contrasting prey of varying trophic levels. Overall, information use and plastic resource selection of individuals with reduced short‐term foraging site fidelity allow predators to overcome prey field lability. Our study is an essential step towards a better understanding of individual responses to enhanced environmental stochasticity driven by global changes, and of pathways favouring population persistence.     

Lifelong foraging and individual specialisation are influenced by temporal changes of resource availability

Resource availability largely determines the distribution and behaviour of organisms. In plant–pollinator communities, availability of floral resources may change so rapidly that pollinator individuals can benefit from switching between multiple resources, i.e. different flowering plant species. Insect pollinator individuals of a given generation often occur in different time windows during the reproductive season. This temporal variation in individual occurrences, together with the rapidly changing resource availability, may lead individuals of the same population to encounter and use different resources, resulting in an apparent individual specialisation. We hypothesized, that 1) individual pollinators change their resource use (flower visitation) during their lifetime according to the changing availability of floral resources, and that 2) temporal variation in individual occurrences of pollinators and in resource availability will partly explain individual specialisation. To test these hypotheses, we observed flower visitations of individually marked clouded Apollo butterflies Parnassius mnemosyne during one reproductive season. We found temporal changes in lifetime individual resource use that followed the changes in resource availability, indicating that butterflies can adjust foraging to varying resource availability. Individuals differed considerably in their resource use. This variation was partly explained by temporal variation in both floral resource availability and temporal occurrence of individual butterflies. We suggest the butterfly as a sequential specialist, i.e. short‐term specialist and long‐term generalist. This foraging plasticity can be essential for short‐living insect pollinators in rapidly changing environments. Although flowering dynamics do not fully explain the variability in foraging, our results highlight the importance of temporal dimension in resource use studies. Ultimately, the relative pace of environmental change compared to individual lifespan may be a key factor in resource use plasticity.     

Florivores prefer white versus pink petal color morphs in wild radish, Raphanus sativus

Many hypotheses suggest that pollinators act to maintain or change floral color morph frequencies in nature, although pollinator preferences do not always match color morph frequencies in the field. Therefore, non-pollinating agents may also be responsible for color morph frequencies. To test this hypothesis, we examined whether Raphanus sativus plants with white flowers received different amounts of florivory than plants with pink flowers, and whether florivores preferred one floral color over the other. We found that white-flowered plants received significantly more floral damage than pink-flowered plants in eight populations over 4 years in northern California. Both generalists and specialists on Brassicaceae preferred white petals in choice and short-term no choice tests. In performance tests, generalists gained more weight on white versus pink petals whereas specialists gained similar amounts of weight on pink and white morphs. Because our results suggest that florivores prefer and perform better on white versus pink flowers, these insects may have the opportunity to affect the frequency of color morphs in the field.     

Fruit size decline from the margin to the center of capitula is the result of resource competition and architectural constraints

Plants produce repeated structures, such as leaves, flowers, and fruits, which differ in size and shape. One example of this is fruit size, which is commonly observed to decrease from proximal to distal positions within an inflorescence. The resource limitation hypothesis proposes that because proximal fruits usually develop first, they have temporal priority on access to resources over distal fruits. The non-mutually exclusive architectural effects hypothesis suggests that these position effects in fruit size may also be due to inherent architectural variation along infructescence axes. We separated out the effects of resource competition and inflorescence architecture by removing the outer or the inner flowers within capitula of Tragopogon porrifolius. We also studied if fruit position influenced germination and seedling performance in order to assess fitness consequences of position effects. Inner fruits were significantly heavier when outer flowers were removed. However, outer fruits did not significantly increase when inner flowers were removed, suggesting later fruits were limited by the development of early fruits. Our findings also suggest that architectural constraints restricted the size of inner fruits in comparison with outer ones. We found that both resource competition and inflorescence architecture affected the fruit size of T. porrifolius, even though this species does not have linear, indeterminate inflorescences. We advance the hypothesis that, when such effects on fitness occur, resource competition-mediated position effects could turn, in evolutionary time, into architectural position effects.     

Petunia flowers solve the defence/apparency dilemma of pollinator attraction by deploying complex floral blends

Flowers recruit floral visitors for pollination services by emitting fragrances. These scent signals can be intercepted by antagonists such as florivores to locate host plants. Hence, as a consequence of interactions with both mutualists and antagonists, floral bouquets likely consist of both attractive and defensive components. While the attractive functions of floral bouquets have been studied, their defensive function has not, and field‐based evidence for the deterrence of floral‐scent constituents is lacking. In field and glasshouse experiments with five lines of transgenic Petunia x hybrida plants specifically silenced in their ability to release particular components of their floral volatile bouquet, we demonstrate that the emission of single floral‐scent compounds can dramatically decrease damage from generalist florivores. While some compounds are used in host location, others prevent florivory. We conclude that the complex blends that comprise floral scents are likely sculpted by the selective pressures of both pollinators and herbivores.     

Floral affinity and benefits of dietary mixing with flowers for a polyphagous scarab, <Emphasis Type="Italic">Popillia japonica</Emphasis> Newman

Many generalist herbivores, especially adult beetles, are facultative florivores, feeding on leaves but readily accepting floral tissues when available. We speculated that day-flying beetles with high energetic requirements would benefit from dietary mixing with nutrient-rich flower tissues and favor them during foraging. We tested that Floral Affinity Hypothesis with Popillia japonica, a day-active ruteline scarab that feeds intermittently throughout its adult life on multiple plant species. In field tests with six species of flowering hosts, far more landings occurred on flowers than on foliage for all plants except Hibiscus syriacus which bears flowers along the main stem rather than terminally. Trials with elevated plants showed that height of the floral display contributes to beetles landing on flowers. Flower petals generally were preferred over leaves in laboratory choice tests. Nitrogen and water content were comparable or higher in foliage than in petals, but plant sugars were much higher in petals. Longevity and fecundity of beetles provided single-plant diets of Hibiscus, Rosa × hybrida, or Trifolium flowers for 3 weeks were as high, or higher, than for beetles fed foliage of Tilia cordata, a highly suitable resource. As expected, rotating flowers or Tilia foliage with marginally suitable Quercus palustris foliage enhanced those parameters relative to a diet of Quercus alone, but beetles provided high-quality Tilia foliage also benefitted from dietary mixing with flowers. Nearly all past dietary mixing studies concerned immature insects, for which growth rate is paramount. Opportunistic florivory by adult beetles represents a type of dietary mixing wherein the premium may be calorie-rich food for fueling flight muscles, with ensuing reproductive benefits.     

Impact of reassociation with a coevolved herbivore on oviposition deterrence in a hostplant

Although selection by herbivores for increased feeding deterrence in hostplants is well documented, selection for increased oviposition deterrence is rarely examined. We investigated chemical mediation of oviposition by the parsnip webworm (Depressaria pastinacella) on its principal hostplant Pastinaca sativa to determine whether ovipositing adults choose hostplants based on larval suitability and whether hostplants experience selection for increased oviposition deterrence. Webworms consume floral tissues and florivory selects for increased feeding deterrents; moths, however, oviposit on leaves of pre-bolting plants. Exclusive use of different plant parts for oviposition and larval feeding suggests oviposition should select for increased foliar deterrents. Recent webworm colonization of New Zealand (NZ) allowed us to assess phenotypic changes in foliar chemicals in response to webworm oviposition. In a common garden experiment, we compared NZ populations with and without a history of infestation from 2004 to 2006 for changes in leaf chemistry in response to oviposition. Three leaf volatiles, cis- and trans-ocimene, and β-farnesene, elicit strong responses in female moth antennae; these compounds were negatively associated with oviposition and are likely oviposition deterrents. Leaf β-farnesene was positively correlated with floral furanocoumarins that deter florivory; greater oviposition on plants with low floral furanocoumarins indicates that moths preferentially oviposit on parsnips most suitable for larval growth. Unlike florivory, high oviposition on leaves did not lower plant fitness, consistent with the fact that NZ parsnip foliar chemistry was unaffected by 3–6 years of webworm infestation. Thus, in this system, selection by ovipositing moths on foliar chemistry is weaker than selection by larvae on floral chemistry.