Plant traits mediate effects of predators across pepper (Capsicum annuum) varieties

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Effect of flower orientation on the male and female traits of Myrtillocactus geometrizans (Cactaceae)

• Intra‐individual variation in the production and size of reproductive traits has been documented in columnar cacti, being higher in equator‐facing flowers. Such variation is attributed to the high amount of PAR intercepted by stems oriented towards the equator. Most studies focused on this phenomenon have documented the existence of intra‐individual variation on traits associated with the female function; however, its impact on traits associated with the male function has been neglected. We tested the hypothesis that equator‐facing flowers of Myrtillocactus geometrizans exhibit higher values on traits associated with both male and female functions than flowers facing against it.
• Number and size of anthers and ovaries, pollen:ovule ratio and number and quality of pollen grains (diameter, germinability, viability and pollen tube length) were estimated from reproductive structures facing north and south, and compared with t‐tests between orientations.
• Number of anthers per flower, number of pollen grains per anther and per floral bud; pollen size, viability and germinability; pollen tube length; ovary length and pollen:ovule ratio were significantly higher in reproductive structures oriented towards the south (i.e. equator).
• These findings suggest that intra‐individual variation in floral traits of M. geometrizans might be associated with different availability of resources in branches with contrasting orientation. Our results provide new evidence of the existence of a response to an orientation‐dependent extrinsic gradient. To our knowledge, this is the first study documenting the existence of intra‐individual variation on pollen quality and P:O ratio in Cactaceae species.

     

Does natural deposition of pine pollen affect the ovipositional behavior of Frankliniella occidentalis and Frankliniella fusca?

Tree pollen, especially Pinus spp. (Pinaceae), is shed in large quantities every spring in North America. Pine pollen deposition onto leaves was found to significantly influence the ovipositional behaviors of certain thrips species (Thysanoptera: Thripidae) in peanut and tomato leaf choice and no‐choice tests. Pine pollen (Pinus elliottii Engelm.) increased the oviposition rate 2.9‐fold for Frankliniella occidentalis (Pergande) (western flower thrips) and 1.6‐fold for Frankliniella fusca (Hinds) (tobacco thrips) in choice tests averaged over both plant species. These results support the idea that pollen has a greater impact on F. occidentalis behavior than on F. fusca behavior. The most dramatic increase was in peanut, where F. occidentalis only oviposited on leaves dusted with pollen, suggesting that the addition of pollen stimulated this flower thrips to lay eggs on a poor host‐plant part. The impact of pollen on the rate of oviposition by thrips is important because it is the early‐instar nymphs that acquire tomato spotted wilt virus (TSWV), which these two thrips species vector. In a laboratory bioassay, the addition of pine pollen to TSWV‐infected peanut foliage increased the percentage of infected F. fusca after one generation.     

Pollen and stigma size changes during the transition from tristyly to distyly in Oxalis alpina (Oxalidaceae)

• Pollen and stigma size have the potential to influence male fitness of hermaphroditic plants, particularly in species presenting floral polymorphisms characterised by marked differences in these traits among floral morphs. In this study, we take advantage of the evolutionary transition from tristyly to distyly experienced by Oxalis alpina (Oxalidaceae), and examined whether modifications in the ancillary traits (pollen and stigma size) respond to allometric changes in other floral traits. Also, we tested whether these modifications are in accordance with what would be expected under the hypothesis that novel competitive scenarios (as in distylous‐derived reproductive system) exert morph‐ and whorl‐specific selective pressures to match the available stigmas.
• We measure pollen and stigma size in five populations of O. alpina representing the tristyly–distyly transition.
• A general reduction in pollen and stigma size occurred along the tristyly–distyly transition, and pollen size from the two anther levels within each morph converged to a similar size that was characterised by whorl‐specific changes (increases or decreases) in pollen size of different anthers in each floral type.
• Overall, results from this study show that the evolution of distyly in this species is characterised not only by changes in sexual organ position and flower size, but also by morph‐specific changes in pollen and stigma size. This evidence supports the importance of selection on pollen and stigma size, which increase fitness of remaining morphs following the evolution of distyly, and raises questions to explore on the functional value of pollen size in heterostylous systems under pollen competition.

     

Positive association between thrips and spider mites in seedling cotton

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Pollination of New CaledonianWinteraceae: Opportunistic shifts or parallel radiation with their pollinators?

Flower visitors on 12 species of New CaledonianWinteraceae were studied. The visitors were two species of ancestral moths (Sabatinca; Micropterigidae), three species of weevils (Palontus; Curculionidae), and a species of thrips. Behavior observations and pollen records suggest that the beetles and occasionally the moths serve as pollinators ofZygogynum and Exospermum, andBelliolum is pollinated primarily by thrips. The floral volatiles are simple in composition, usually dominated by short esters. Preliminary experiments showed that ethyl acetate elicited alighting, and a distinctive huddling behavior was elicited by artificially mixed fragrance. The host associations of otherSabatinca andPalontus spp. do not support the hypothesis that theWinteraceae have radiated in association with their pollinators. The available evidence supports the notion of opportunistic isolated host colonizations at some point in the radiation of the pollinator groups.     

Is body size a good indicator of fecundity in the genus Thaumetopoea? A story told by two intrageneric Mediterranean forest defoliators

1. Body size correlates with several factors such as reproductive fitness, environmental changes, the quality and quantity of food during critical development stages, and the feeding season. For the Palearctic moths of the genus Thaumetopoea (Lepidoptera; Notodontidae), the larval development is crucial and differs between species according to their feeding season; larvae of the pine processionary moth Thaumetopoea pityocampa (Denis & Schiffermüller 1775) feed during winter while larvae of its congeneric cedar processionary moth Thaumetopoea bonjeani (Powell 1922) develop during summer in North Africa.
2. This discrepancy in lifecycles leads to different reproductive traits such as egg batch length, number of eggs per batch, eggs protection mechanisms and female body size.
3. According to Darwin's fecundity advantage hypothesis (1871), female body size should have a positive influence on reproductive fitness, since larger females supposedly have higher fecundity. The universal allometric scaling phenomenon rule proposed by Rensch (1950) predicts that the degree of sexual size dimorphism tends to decrease with the increase of female body size.
4. Here, two morphometrical parameters that is, body size and scale size, estimated from body measurements of individuals of both species, feeding on the same host Atlantic cedar Cedrus atlantica (Manetti & Carrière 1855) (Pinales; Pinaceae) in Algeria were proposed. The aim was to find out traits that might rule the competition for food and space, in particularly fecundity and body size.
5. Results of the present study highlight a female-biased sexual size dimorphism in both species. The positive correlation between female body size and fecundity shown in this study weakly supports Darwin's hypothesis. Finally, the intrageneric test performed leads to conclude that Rensch's rule does not hold in the considered species.

     

Size and sex allocation in monoecious woody plants

The female size advantage hypothesis predicts that the allocation ratio of female: male reproductive effort should increase with plant size (total reproductive effort). A male height advantage hypothesis has also been proposed, based on the supposed greater advantage of height to male reproductive success in wind-pollinated plants. These ideas were tested with data for wind-pollinated, monoecious trees and shrubs which exhibit a suitably large range of sizes. Number of male inflorescences increased faster with size than did number of female inflorescences in 2 of 9 species; in the remaining 7 species there was no significant difference. The male:female ratio of inflorescence numbers increased with height in 4 of 7 species and did not change significantly in the remaining 3 species, as shown by regression. Height and size are highly correlated and so their effects could not be distinguished. The fact that many conifers place the female cones uppermost in the crown suggests that size and not height favors increased allocation to male function, as does well-established theory connecting the existence of male versus female size advantage to pollen and seed dispersal chacteristics. Regression analysis of the relation between male and female reproductive effort should be done by reduced major axis regression; ordinary least squares regression underestimates slopes; in this study opposite conclusions could be drawn from ordinary least squares and reduced major axis regressions.     

Size and sex of cricket prey predict capture by a sphecid wasp

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The hosts and distribution of British thrips

• 1 The host relationships and distribution of the 146 ‘native’ species of British thrips are reviewed.
• 2 The spermatophyte hosts, the species of thrips breeding on each plant taxon, and the mycophagous and ‘predatory’ species are listed.

     

Life history characteristics of Frankliniella occidentalis on cucumber leaves with and without supplemental food

The development time, fecundity, longevity, and resultant intrinsic growth rate of the western flower thrips Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidae] encaged on a cucumber leaf were compared among seven types of food supplied: six pollen species and a mixture of milk powder and yeast. The rationale was to find a food source that offers the least benefit for thrips and could therefore be considered as a food source for the preventative introduction of thrips predators. With the exception of the mixture of milk powder and yeast, all the food sources tested offered a nutritional benefit for the thrips. The addition of pollen increased fecundity and reduced development time, mainly during the larval stage. Betula pubescens and Corylus avellana pollen also increased adult longevity. The nutritional benefit of Pinus sylvestris pollen was greater than that of the other five pollen species, as manifested by its significantly greater positive effect on fecundity. The other pollen species could not be ranked in terms of nutritional benefit to F. occidentalis. The negative effect of the milk powder plus yeast mix on the life‐table parameters of F. occidentalis probably only occurs in an encaged situation where thrips cannot escape from the unfavorable environment. The crude estimate of the intrinsic growth rate of F. occidentalis increased from 0.163 on the plain cucumber leaf to 0.240 when P. sylvestris pollen was added to the leaf. The differences in intrinsic growth rate mainly reflect the differences in fecundity among the food sources. Thus, the peak oviposition rate may be used as a measure of the nutritional benefit F. occidentalis can obtain by feeding on supplemental food sources. The positive effect of a supplemental food source on thrips does not necessarily mean it is unsuitable for the preventative introduction of thrips predators, because the supplemental food can also affect the population dynamics of the predator and the predator–prey interaction and, hence, the outcome of biological control.     

The effect of host developmental stage at parasitism on sex‐related size differentiation in a larval endoparasitoid

• 1 For their larval development, parasitoids depend on the quality and quantity of resources provided by a single host. Therefore, a close relationship is predicted between the size of the host at parasitism and the size of the emerging adult wasp. This relationship is less clear for koinobiont than for idiobiont parasitoids.
• 2 As size differentiation in host species exhibiting sexual size dimorphism (SSD) is likely to occur already during larval development, in koinobiont larval endoparasitoids the size of the emerging adult may also be constrained based on the sex of the host caterpillar.
• 3 Sex‐specific growth trajectories were compared in unparasitised Plutella xylostella caterpillars and in second and fourth instar hosts that were parasitised by the solitary larval koinobiont endoparasitoid Diadegma semiclausum. Both species exhibit SSD, where females are significantly larger than males.
• 4 Healthy female P. xylostella caterpillars developed significantly faster than their male conspecifics. Host regulation induced by D. semiclausum parasitism depended on the instar attacked. Parasitism in second‐instar caterpillars reduced growth compared to healthy unparasitised caterpillars, whereas parasitism in fourth‐instar caterpillars arrested development. The reduction in growth was most pronounced in hosts producing male D. semiclausum.
• 5 Parasitism itself had the largest impact on host growth. SSD in the parasitoid is mainly the result of differences in growth rate of the parasitoid–host complex producing male and female wasps and differences in exploitation of the host resources. Female wasps converted host biomass more efficiently into adult biomass than males.

     

Functional anatomy reveals secretory activity in papillose anthers of a buzz‐pollinated Solanum species (Cyphomandra clade – Solanaceae)

• Pollination in Solanum (Solanaceae) species is commonly performed by female bees, which vibrate anthers to extract pollen. Another pollen removal type is by male euglossine bees, milking the anthers when searching for floral scents produced by secretory tissues (osmophorous) at the swollen connective of the anthers of species in the Cyphomandra clade. Some species of this clade, however, are buzz‐pollinated and present papillate anthers that should also have secretory activity, a hypothesis here tested.
• The anthers of Solanum luridifuscescens were fixed at different stages of development and analysed under light microscopy, SEM and TEM. Histochemical tests for the detection of starch and lipids were done.
• Epidermal cells of the abaxial surface of the anthers were visibly papillose, had large nuclei and dense cytoplasm rich in organelles such as mitochondria and plastids, typical features of secretory tissues. In this site, lipid droplets were detected, concomitantly with starch consumption, compatible with the secretory process in osmophores. No exudate or accumulation of substances was seen on the surface; in agreement with a previous pollination study performed in field conditions, where no pollinators were observed collecting floral scents, only pollen. The histochemical and structural analyses have evidenced the lipidic composition of the secretion, strongly pointing to terpenes as the secreted compounds.
• Ours findings show that papillae of the anthers have secretory activities that produce lipophilic compounds. This does not result in resources for bees, but could be an evolutionary step to the development of more specialised anthers in the Cyphomandra clade.

     

Phylogeny determines flower size‐dependent sex allocation at flowering in a hermaphroditic family

• In animal‐pollinated hermaphroditic plants, optimal floral allocation determines relative investment into sexes, which is ultimately dependent on flower size. Larger flowers disproportionally increase maleness whereas smaller and less rewarding flowers favour female function. Although floral traits are considered strongly conserved, phylogenetic relationships in the interspecific patterns of resource allocation to floral sex remain overlooked. We investigated these patterns in Cistaceae, a hermaphroditic family.
• We reconstructed phylogenetic relationships among Cistaceae species and quantified phylogenetic signal for flower size, dry mass and nutrient allocation to floral structures in 23 Mediterranean species using Blomberg's K‐statistic. Lastly, phylogenetically‐controlled correlational and regression analyses were applied to examine flower size‐based allometry in resource allocation to floral structures.
• Sepals received the highest dry mass allocation, followed by petals, whereas sexual structures increased nutrient allocation. Flower size and resource allocation to floral structures, except for carpels, showed a strong phylogenetic signal. Larger‐flowered species allometrically allocated more resources to maleness, by increasing allocation to corollas and stamens.
• Our results suggest a major role of phylogeny in determining interspecific changes in flower size and subsequent floral sex allocation. This implies that flower size balances the male–female function over the evolutionary history of Cistaceae. While allometric resource investment in maleness is inherited across species diversification, allocation to the female function seems a labile trait that varies among closely related species that have diversified into different ecological niches.

     

Heat and drought determine flower female allocation in a hermaphroditic Mediterranean plant family

• In animal‐pollinated hermaphroditic species, larger and xenogamous flowers increase male‐biased resource allocation, whereas smaller and selfing flowers invest disproportionally more resources to female function. In Cistaceae, an entomophilous and hermaphroditic Mediterranean family, this pattern generally follows a phylogenetic signal. However, resource allocation to carpels is independent of phylogeny, which suggests trait divergences among closely related species during the diversification into different environmental conditions.
• We tested this hypothesis across 37 species of Cistaceae along a temperature and precipitation gradient, including semiarid, dry, subhumid and humid sites. We quantified the proportions of dry mass and nutrient investment to carpels and tested the influence of the climatic gradient and site‐specific precipitation on the interspecific variation in carpel resource allocation.
• Lowest and highest percentages of resource allocation to carpels ranged from 1.5–4.2% to 24.2–36.6%, respectively. The proportion of resources comprised in carpels significantly decreased with increasing precipitation/decreasing temperature. Thus, carpels comprised proportionally more resources under drier and hotter conditions, especially in semiarid sites.
• Our results demonstrate how the extent of climatic constraints is more important than phylogenetic relationships in determining stress‐induced differences in carpel resource allocation across species of Cistaceae in a Mediterranean environment. We suggest that allocation of proportionally more resources to carpels in drier and hotter sites lies within a strategy to deal with the most stressful conditions by means of a high reproductive effort.

     

Pollen size evolution: correlation between pollen volume and pistil length in Asteraceae

Based on the assumptions that pollen tube length is predetermined by provisions in the pollen and that it is a function of pistil length, I hypothesise that species with longer pistils will have larger pollen grains than species with shorter pistils, and that pistil length and pollen size will be positively correlated in a linear manner. To test this hypothesis, the relationship between pollen grain volume and pistil length was compared in 43 Asteraceae species from Argentina. A positive linear correlation was found between pollen volume and pistil length. This correlation remained significant even after potential effects of phylogenetic relatedness were removed. The maintenance of this correlation suggests that in Asteraceae the association between pistil length and pollen volume may reflect a functional rather than a phyletic relationship. In addition, the pistil length: pollen volume ratio (PPR) was analysed in relation to the phylogenetic position of the species. High values of PPR would imply a reduction of the male gametophyte in relation to the minimal volume that a pollen grain must have to grow and fertilise an ovule. Thus, the general pattern of pollen volume reduction in relation to pistil length previously found among many angiosperm families will be also present within a family, i.e., PPR values of derived Asteraceae would be higher than those of basal species. Results indicated that reduction of pollen volume in derived Asteraceae was three times greater than the concomitant shortening of pistil length. Consequently, PPR increased with the phylogenetic position of the taxa. This work supports the correlation between pistil and pollen characters previously found for other plant families and confirms the influence of post-pollination processes on pollen size evolution. Received: 4 November 1999 / Revision accepted: 14 February 2000     

Thrips see red – flower colour and the host relationships of a polyphagous anthophilic thrips

Abstract 1. The common blossom thrips, Frankliniella schultzei, is a polyphagous anthophilic species that colonises a wide range of host‐plant species across different plant taxa. The environmental cues used by these polyphagous insects to recognise and locate host plants are not known. We therefore determined if colour is an important environmental signal used by F. schultzei to recognise flowers of eight of its more significant host‐plant species. 2. The effect of flower colour on the colonisation of different host plant species by F. schultzei was investigated by collecting and analysing the following: (a) numbers of thrips from different heights and aspects of the primary host plant Malvaviscus arboreus, (b) thrips distribution within flowers of Hibiscus rosasinensis, (c) colour reflectance from flowers of eight different host‐plant species, and (d) reflectance from different coloured sticky traps and the number of thrips trapped on them at different times of the day and on different dates. 3. The results indicate that: (a) the thrips (both sexes) concentrate towards the top of the primary host plant M. arboreus and are not distributed differentially according to sunny or shady aspect of the plant, (b) the number of female thrips on H. rosasinensis was higher in anthers compared to petals (corolla) and the basal parts of the flower, and males were as numerous on the petals as were females, and (c) there is a common floral reflectance pattern (but with different intensities) across the eight host plant species, mainly in the red part of the spectrum (600–700 nm). 4. Results of colour sticky trapping show that red attracts more female thrips compared to any other colour and that most were caught between 09.00 and 11.00 hours. By contrast, more male thrips were trapped between 07.00 and 09.00 hours. Males were more evenly distributed across the different colours but the highest numbers were associated with the yellow traps. 5. The higher densities of thrips at the top of their host plant may be related to the early morning (07.00–11.00 hours) activity of the thrips, when the top portions of the plant are more exposed to sunlight. The sex‐related distributions of F. schultzei thrips across time, coloured sticky traps, and various parts of the flowers seem to be related to mating swarm formation by the males, on the one hand, and the relative frequency and intensity of the use of M. arboreus by the females, on the other, as a feeding and oviposition site. Frankliniella schultzei females respond more strongly to red than to any other colours, so it is predicted that the spectral properties of colour recognition by this species will correlate with the predominant red reflectance of its primary host, M. arboreus, and that there may well be a sex‐related difference in colour recognition within this species.     

Territoriality and fighting in a colonial thrips, Hoplothrips pedicularius, and sexual dimorphism in Thysanoptera

ABSTRACT.

• 1 Hoplothrips pedicularius (Haliday) (Thysanoptera: Phlaeothripidae), a tubuliferan thrips in which males possess greatly enlarged forelegs, lives in colonies on Stereum fungus.
• 2 Females oviposit onto communal egg masses, and males fight by grasping and stabbing with their forelegs in territorial defence of oviposition areas. Prolonged escalated fights occur between males who are of similar size.
• 3 Larger males usually win fights and become dominant at the oviposition area. Dominant males secure 80% of matings, and mate most frequently during oviposition periods, with an ovipositing female.
• 4 Smaller, subordinate males avoid fights and attempt to 'sneak’copulations. However, they occasionally challenge the dominant male. Challenges tend to follow copulations by the subordinate male and occur more frequently between males who are of similar size.
• 5 Subordinate males who eventually leave the oviposition area are larger than those who remain, have frequently challenged the dominant male, and have more frequently been stabbed.
• 6 Sexual dimorphism in thrips is associated with gregariousness, claustral habitats, female-biased sex ratios, and male winglessness. In thrips genera in which males exhibit foreleg armature, males are larger relative to females. The ecological circumstances promoting sexual dimorphism and male fighting in spatially-structured populations are discussed.

     

The coincidence of thrips and dispersed pollen in PNRSV-infected stonefruit orchards – a precondition for thrips-mediated transmission via infected pollen

Recent laboratory studies have demonstrated that Prunus necrotic ringspot virus (PNRSV) (family Bromoviridae) can be readily transmitted when thrips and virus‐bearing pollen are placed together on to test plants. For this transmission mechanism to result in stonefruit tree infection in the field, PNRSVbearing pollen must be deposited onto surfaces of stonefruit trees on which thrips also occur. In a previous paper, we demonstrated that almost all pollen in a PNRSV‐infected Japanese plum orchard in southeastern Queensland was deposited onto flowers, whereas few grains occurred on leaves and none on stems. Here, we present results of our investigation of thrips species composition, distribution and abundance on stonefruit trees in the same study area as our previous pollen deposition study. We collected a total of 2010 adult thrips from 13 orchards during the 1989, 1991 and 1992 flowering seasons of which all but 14 were in the suborder Terebrantia. Most (97.4%) terebrantian thrips were of three species, Thrips imaginis, Thrips australis and Thrips tabaci. Thrips tabaci as well as species mixtures that included T. imaginis, T. australis and T. tabaci have been shown to transmit PNRSV via infected pollen in laboratory tests. Adult thrips were frequently collected from flowers but rarely from leaves and never from stems. Large and significant differences in numbers of T. imaginis, T. australis and T. tabaci adults in flowers occurred among orchards and between seasons. No factor was conclusively related to thrips numbers but flowers of late‐flowering stonefruit varieties tended to hold more thrips than those of early‐flowering varieties. Our results indicate that the common thrips species present on stonefruit trees in the Granite Belt are also ones previously shown to transmit PNRSV via infected pollen in the laboratory and that these thrips are concentrated in tonefruit flowers where most stonefruit pollen is deposited. These results contribute to mounting circumstantial evidence that stonefruit flowers may be inoculated with PNRSV via an interaction of thrips with virus‐bearing pollen and that this transmission mechanism may be an important cause of new tree infections in the field     

The developmental strategies and related profitability of an idiobiont ectoparasitoid Sclerodermus pupariae vary with host size

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