Allocation to reproduction following experimental defoliation in Platanthera bifolia (Orchidaceae)

The roles of herbivory and pollination success in plant reproduction have frequently been examined, but interactions between these two factors have gained much less attention. In three field experiments, we examined whether artificial defoliation affects allocation to attractiveness to pollinators, pollen production, female reproductive success and subsequent growth in Platanthera bifolia L. (Rich.). We also recorded the effects of inflorescence size on these variables. We studied the effects of defoliation on reproductive success of individual flowers in three sections of inflorescence. Defoliation and inflorescence size did not have any negative effects on the proportion of opened flowers, spur length, nectar production or the weight of pollinia. However, we found that hand-pollination increased relative seed production and defoliation decreased seed set in most cases. Interactions between hand-pollination and defoliation were non-significant indicating that defoliation did not affect female reproductive success indirectly via decreased pollinator attraction. Plants with a large inflorescence produced relatively more seeds than plants with a small inflorescence only after hand-pollination. The negative effect of defoliation on relative capsule production was most clearly seen in the upper sections of the inflorescence. In addition to within season effects of leaf removal, defoliated P. bifolia plants may also have decreased lifetime fitness as a result of lower seed set within a season and because of a lower number of reproductive events due to decreased plant size (leaf area) following defoliation. Our study thus shows that defoliation by herbivores may crucially affect reproductive success of P. bifolia.     

Florivorous myrmecophilous caterpillars exploit an ant–plant mutualism and distract ants from extrafloral nectaries

Females of myrmecophilous butterflies tend to oviposit in plants visited by ant species that engage in stable associations with its larvae. In Banisteriopsis malifolia, caterpillars are attended by the same ants that feed on extrafloral nectaries. A conflict may arise when both the plant and caterpillars compete for ant attention, and ants are assumed to forage on the highest quality resource. By attending caterpillars, ants can be indirectly detrimental to plant fitness because florivorous larvae feed intensively until pupation. In this study, we specifically investigated (i) whether the occurrence of facultative myrmecophilous Synargis calyce (Riodinidae) caterpillars in B. malifolia was based on ant species (Camponotus blandus or Ectatomma tuberculatum) and abundance; (ii) the monopolization of ants by the butterfly larvae and (iii) the florivory rates incurred by the caterpillars on inflorescences. The abundance of S. calyce was six‐fold greater in plants with C. blandus, compared to E. tuberculatum treatments. Caterpillars monopolized up to 50% of C. blandus on the plants, indicating that the resources offered by S. calyce were more attractive to ants than extrafloral nectaries. Florivory by riodinids incurred losses of almost 60% of flower buds. Myrmecophilous riodinids exploited an ant–plant mutualism by attracting aggressive ants that become larvae bodyguards. Thus, this ecological interaction is potentially detrimental to B. malifolia, since the ants, which can provide protection against herbivores, shift to provide defence for one of these herbivores.     

Order of herbivore arrival on wild cabbage populations influences subsequent arthropod community development

In plant–arthropod associations, the first herbivores to colonise a plant may directly or indirectly affect community assembly on that particular plant. Whether the order of arrival of different arthropod species further modulates community assembly and affects plant fitness remains unclear. Using wild Brassica oleracea plants in the field, we manipulated the order of arrival of early‐season herbivores that belong to different feeding guilds, namely the aphid Brevicoryne brassicae and caterpillars of Plutella xylostella. We investigated the effect of herbivore identity and order of arrival on community assembly on two B. oleracea plant populations during two growth seasons. For this perennial plant, we evaluated whether foliar herbivory also affected herbivore communities on the flowers and if these interactions affected plant seed production. Aphid infestation caused an increase in parasitoid abundance, but caterpillars modulated these effects, depending on the order of herbivore infestation and plant population. In the second growth season, when plants flowered, the order of infestation of leaves with aphids and caterpillars more strongly affected abundance of herbivores feeding on the flowers than those feeding on leaves. Infestation with caterpillars followed by aphids caused an increase in flower‐feeding herbivores compared to the reversed order of infestation in one plant population, whereas the opposite effects were observed for the other plant population. The impact on plant seed set in the first reproductive year was limited. Our work shows that the identity and arrival order of early season herbivores may have long‐term consequences for community composition on individual plants and that these patterns may vary among plant populations. We discuss how these community processes may affect plant fitness and speculate on the implications for evolution of plant defences.     

Foraging behavior of Brachygastra lecheguana (Hymenoptera: Vespidae) on Banisteriopsis malifolia (Malpighiaceae): Extrafloral nectar consumption and herbivore predation in a tending ant system

In the Brazilian savanna many plant species bear regular associations with patrolling ants that are aggressive towards insect herbivores. However, not only ants but also several species of predatory wasps are attracted to plants due to the extrafloral nectaries (EFNs). Such wasps feed on both herbivores and plant exudates. In this study we describe the foraging behavior of the social Polistinae wasp Brachygastra lecheguana in the extrafloral nectaried shrub Banisteriopsis malifolia, and investigated the influence of patrolling ants Camponotus blandus on the activity of the wasp. Brachygastra lecheguana fed on the endophytic larvae of Anthonomus (Curculionidae) beetles that developed inside flower buds. The wasp lacerated the bud layers to reach the beetle larvae located at the bud core. The wasp visits to Ba. malifolia were statistically related to the abundance of flower buds and beetles. Ant exclusion experiments revealed that the hunting behavior of B. lecheguana on beetles was not related to the absence of C. blandus. However we found that wasps spent more time consuming extrafloral nectar on branches where ants were excluded. This is the first study reporting extrafloral nectar consumption by B. lecheguana, as well as the predation on herbivores in natural areas. In cerrado vegetation, ants benefit the plant by reducing insect herbivores, and our study provides evidence that the B. lecheguana – Ba. malifolia system represents a potential interaction where the wasp may also benefit the host plant. The value of this wasp species as a plant‐guard is discussed.     

Extrafloral nectaries as a deterrent mechanism against seed predators in the chemically protected weed Crotalaria pallida (Leguminosae)

Abstract In several plants, extrafloral nectaries (EFN) are located close to the reproductive structures, suggesting that ants may act as a defence against specialized seed predators that overcome chemical defences. Alternatively, ants may also deter herbivores in a generalized manner, thereby protecting the whole plant. In this work, we examined the relationship between the chemically protected weed Crotalaria pallida Ait. (Leguminosae) that bears EFN, its specialized seed predator, the larvae of the arctiid moth Utetheisa ornatrix L. (Arctiidae) and ants. We tested two hypotheses related to the type of deterrence caused by ants. The Seed Predator Deterrence Hypothesis predicts that ant deterrence is directed primarily towards herbivores that destroy seeds and other reproductive structures, without attacking herbivores on vegetative structures. The General Deterrence Hypothesis states that ants are general in their effects, equally deterring herbivores in vegetative and reproductive structures. Our results supported the predictions of the Seed Predator Deterrence Hypothesis, namely, that (i) ant activity on EFN was related to the vulnerability of reproductive structures to attack by U. ornatrix; (ii) ant patrolling was restricted almost entirely to racemes; (iii) ants removed termites used as baits more frequently on racemes than on leaves; and (iv) U. ornatrix larvae were often expulsed from the racemes. These results indicate that EFN can act as another deterrent mechanism in chemically protected plants by promoting the expulsion of specialist seed predators.     

Control of fecundity through abortion in Epilobium montanum L.

Summary Plants of the inbreeding perennial herb Epilobium montanum L. were defoliated at two stages in development and the formation and abortion of flower buds, flowers, copsules and ovules was compared with control plants. A comparison was also made of the effects of self- and cross-pollination on fecundily. Defoliation reduced the number of flower buds formed but its greatest effect was to increase the abortion of flower buds. Defoliation also caused earlier abortions which were generally lower on the racemes of the treated than on the control plants. The abortion of flowers and capsules was much less significant. The number of ovules formed per capsule decreased with height on the raceme and the abortion rate of ovules was increased by defoliation. The pattern of ovule abortion within the capsules differed between cross- and self-pollinated plants but the number of seeds ripened was not affected. The overall survivorship of ovules to mature seeds was 89.3% which compares with the average of 85% found by Wiens for inbreeding annuals. The findings suggest that such high values of ovule survivorship may be characteristics of normally inbreeding species irrespective of whether they are annuals or perennials.     

Characterization of the damage of Spodoptera eridania (Cramer) and Spodoptera cosmioides (Walker) (Lepidoptera: Noctuidae) to structures of cotton plants

The cotton plant, Gossypium hirsutum, hosts various pests that damage different structures. Among these pests, Spodoptera cosmioides (Walker) and Spodoptera eridania (Cramer) (Lepidoptera: Noctuidae) are considered important. The objectives of this study were to characterize and to quantify the potential damage of S. eridania and S. cosmioides feeding on different structures of cotton plants. For this purpose, newly-hatched larvae were reared on the following plant parts: leaf and flower bud; leaf and boll; flower bud or boll; and leaf, flower bud and boll. The survival of S. cosmioides and S. eridania was greater than 80% and 70% for larvae fed on cotton plant parts offered separately or together, respectively. One larva of S. eridania damaged 1.7 flower buds, but did not damage bolls, while one larva of S. cosmioides damaged 5.2 flower buds and 3.0 cotton bolls. Spodoptera eridania and S. cosmioides can be considered species with potential to cause economic damage to cotton plants because they can occur throughout cotton developmental stages causing defoliation and losses of reproductive structures. Therefore, the results validate field observations that these two species of Spodoptera are potential pests for cotton.     

Interactive effects of soil fertility and herbivory on Brassica nigra

Soil nutrient availability may affect both the amount of damage that plants receive from herbivores and the ability of plants to recover from herbivory, but these two factors are rarely considered together. In the experiment reported here, I examined how soil fertility influenced both the degree of defoliation and compensation for herbivory for Brassica nigra plants damaged by Pieris rapae caterpillars. Realistic levels of defoliation were obtained by placing caterpillars on potted host plants early in the life cycle and allowing them to feed until just before pupation on the designated plant. Percent defoliation was more than twice as great at low soil fertility compared to high (48.2% and 21.0%, respectively), even though plants grown at high soil fertility lost a greater absolute amount of leaf area (38.2 cm² and 22.1 cm², respectively). At both low and high soil fertility, total seed number and mean mass per seed of damaged plants were equivalent to those of undamaged plants. Thus soil fertility did not influence plant compensation in terms of maternal fitness. However, the pathways used to achieve compensation in seed production were different at low and high soil fertility. At low soil fertility, relative leaf growth rates (area added per inital area per day) of damaged plants were drastically reduced over the second week of caterpillar feeding. Damaged plants recovered the leaf area lost to herbivory in the two weeks following insect removal by increasing leaf relative growth rates above the levels seen for undamaged plants, but the replacement of leaf tissue lost to herbivory came at the expense of stem biomass. At high soil fertility, relative leaf growth rates of damaged plants were similar to those of undamaged plants both over the second week of caterpillar feeding and following caterpillar removal, and stem biomass was not affected by herbivory. These results suggest that higher levels of soil nutrients increased the ability of plants to stay ahead of their herbivores as they were being eaten. Because damaged plants at high soil fertility were able to maintain leaf growth rates to a greater extent than damaged plants at low soil fertility, they did not fall as far behind undamaged plants over the period of insect feeding and did not have as much catching up to do after feeding ended to compensate for herbivory.     

Consequences of variation in flowering phenology for seed head herbivory and reproductive success in Erigeron glaucus (Compositae)

Summary We examined the relationship between flowering phenology, reproductive success (seed production only), and seed head herbivory for 20 similarly sized clones of Erigeron glaucus growing at Bodega Bay Reserve, northern California, USA. Although clones tended to reach peak flowering on the same date, they differed in the proportion of their total flowers produced around that date (flowering synchrony). Clones also differed in the number and density of flower heads presented at any one time to pollinators and herbivores (floral display). Both of these characteristics had consequences for herbivory and plant reproductive success. The proportion of flower heads damaged by insect herbivores was greater for clones that concentrated flowering activity during the main flowering period for the population as a whole (high synchrony) compared to clones that spread flowering out temporally. The primary reason for this result was that clones with low flowering synchrony produced a significant proportion of their flower heads during the fall and therefore, escaped attack by the tephritid fly, Tephritis ovatipennis. Clones with intermediate synchrony had lower seed success (total number of viable seeds produced over the year) than clones with either low or high synchrony. The proportion of flower heads damaged by insect herbivores and number of tephritid flies reared from flower heads were both negatively correlated to floral display while seed head mass and germination rates were positively related to display. Thus, clones which produced dense floral displays were favored both in terms of reduced herbivory and increased successful seed production.     

Multiple herbivores and coevolutionary interactions in an Ipomopsis hybrid swarm

Studies focusing on pairwise interactions between plants and herbivores may not give an accurate picture of the overall selective effect of herbivory, given that plants are often eaten by a diverse array of herbivore species. The outcome of such interactions may be further complicated by the effects of plant hybridization. Hybridization can lead to changes in morphological, phenological and chemical traits that could in turn alter plant–herbivore interactions. Here we present results from manipulative field experiments investigating the interactive effects of multiple herbivores and plant hybridization on the reproductive success of Ipomopsis aggregata formosissima X I. tenuituba. Results showed that ungulate herbivores alone had a net positive effect on plant relative fitness, increasing seed production approximately 2-fold. Caterpillars had no effect on plant relative fitness when acting alone, with caterpillar-attacked plants producing the same number of flowers, fruits and seeds as the uneaten controls. Caterpillars, however, significantly reduced flower production of ungulate browsed plants. Flower production in these plants, however, was still significantly greater (approximately 1.7-fold greater) than uneaten controls, likely leading to an increase in reproductive success through the paternal component of fitness given that fruit and seed production was not significantly different from that of herbivore-free controls. Although results suggest that herbivore imposed selection is pairwise, ungulates likely have a large influence on the abundance of, and hence the amount of damage caused by, caterpillar herbivores. Thus, because of the ecological interactions between ungulates and caterpillars, selection on Ipomopsis may be diffuse rather than pairwise, assuming such interactions translate into differential effects on plant fitness as herbivore densities vary. Plant hybridization had no significant effect on patterns of ungulate or caterpillar herbivory; i.e., no significant interactions were detected between herbivory and plant hybridization for any of the fitness traits measured in this study nor did plant hybridization have any significant effect on host preference. These results may be due to patterns of introgression or the lack of species-specific differences between I. aggregate formosissima and I. tenuituba. Plant hybridization per se resulted in lowered reproductive success of white colored morphs due in part to the effects of pollination. Although it appears that there would be strong directional selection favoring darker flower colors due to the lower reproductive success of the white colored morphs in the short run, the natural distribution of hybrids suggest that over the long run selection either tends to average out or there are no fitness differences among morphs in most years due to the additive fitness effects of hawkmoth and hummingbird pollinators.     

Parasitoid-plant mutualism: parasitoid attack of herbivore increases plant reproduction

We tested whether a plant's life time seed production is increased by parasitization of herbivores in a tritrophic system, Arabidopsis thaliana (Brassicaceae) plants, Pieris rapae (Lepidoptera: Pieridae) caterpillars and the solitary endoparasitoid Cotesia rubecula (Hymenoptera: Braconidae). We established seed production for intact A. thaliana plants, plants that were mechanically damaged, plants fed upon by parasitized caterpillars and plants fed upon by unparasitized caterpillars. In the first experiment, with ecotype Landsberg (erecta mutant), herbivory by unparasitized P. rapae caterpillars resulted in a strongly reduced seed production compared to undamaged plants. In contrast, damage by P. rapae caterpillars that had been parasitized by C. rubecula did not result in a significant reduction in seed production. For the second experiment with the ecotype Columbia, the results were identical. Plants damaged by unparasitized caterpillars only produced seeds on regrown shoots. Seed production of plants that had been mechanically damaged was statistically similar to that of undamaged plants. Production of the first ripe siliques by plants fed upon by unparasitized caterpillars was delayed by 18–22 days for Landsberg and 9–10 days for Columbia. We conclude that parasitization of P. rapae by C. rubecula potentially confers a considerable fitness benefit for A. thaliana plants when compared to plants exposed to feeding damage by unparasitized P. rapae larvae. Plants that attract parasitoids and parasitoids that respond to herbivore-induced plant volatiles will both experience selective advantage, justifying the use of the term mutualism for this parasitoid-plant interaction. This type of mutualism is undoubtedly very common in nature.     

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.     

Predispersal mortality and fecundity in the grey mangrove (Avicennia marina) in southeastern Australia

Abstract The predispersal mortality of floral buds and fruits in the grey mangrove (Avicennia marina) was examined over a range of populations for 3 years. The average survival of floral buds to anthesis was 34%. Moth larvae (subtribe Phycitina) attack and consume the contents of variable numbers of flower buds, but their activities did not influence bud survival, as experimental exclusion of larvae did not increase the number of buds surviving to anthesis. Fruit mortality is initially high with an average of 21% of floral buds surviving to immature fruit. Subsequent mortality is lower until on average 2.9% of floral buds survive to become viable propagules. Several cohorts of the phycitine moth larvae feed throughout the development of the fruit, and up to 62% of mature fruit show signs of larval attack. Experimental exclusion of moth larvae doubled the survival of fruits. However more than 75% of fruit mortality may be attributed to maternal regulation. Hail storms can also cause fruit mortality. The potential fecundity (number of ovules) of A. marina was measured over a range of age-size classes of trees and the realized fecundity (viable propagules) was estimated from average predispersal mortality. These estimates were subsequently verified in the field. A fecundity schedule was constructed with assumptions on reproductive frequency and reproductive life. The average annual supply of propagules over a lifetime is estimated to be about 247 viable propagules per tree.     

Factors affecting the development of Botrytis cinerea (grey mould) on linseed (Linum usitatissimum) buds, flowers and capsules

A key was produced to describe 10 stages of development of linseed buds, flowers and capsules. Botrytis cinerea conidia germinated more rapidly and germ tubes grew longer on linseed stigmas, petals and mature senescing capsules than on green leaves, sepals and immature capsules. The proportion of conidia which germinated increased and the germ tubes continued growing for longer in the presence of linseed pollen and flower petal extracts. In controlled environment and field experiments, the response of buds, flowers and capsules to inoculation with B. cinerea changed with stage of development; few pre‐flowering buds developed symptoms (brown lesions, then grey mould), but high proportions of flowering and post‐flowering buds did so. Few immature green capsules developed symptoms and the proportion of capsules which developed symptoms increased as they matured. The presence of linseed pollen decreased the incubation period from inoculation with spore suspensions to appearance of B. cinerea symptoms on buds. A disease cycle was produced to suggest the changes in susceptibility of linseed to infection by B. cinerea conidia during bud, flower and capsule development.     

Factors affecting regulation of maternal investment in an indeterminate flowering plant (Cercidium microphyllum; Fabaceae)

On palo verde trees, nearly 80% of potential offspring were lost during flower bud development. Flower buds at the base of racemes developed earliest and were more likely to survive depredations of gelechiid larvae or abortion from putative limited resources. Herbivory accounted for greater cumulative losses than putative resources; however, an herbivore exclusion experiment suggested that buds damaged by herbivores would have aborted anyway without damage. In a natural experiment, plants that received water runoff had significantly higher densities of racemes, with only slight increases in numbers of buds, flowers, or pods per raceme. Similarly, thinning racemes experimentally to assess limited resources among potentially competing racemes increased the number of viable flower buds per raceme only slightly, with negligible herbivore damage. The production of more racemes rather than more reproductive structures per raceme may be a mechanism to allocate limited resources more efficiently. Alternatively, in studies with animals, similar patterns in the production of broods are thought to be mechanisms to avoid nest predation. Thus, while putative limited resources and resource allocation patterns reduced the proximate effects of larvae, herbivory must be considered as a possible ultimate factor in the patterns observed here because limited resources may be allocated in ways to reduce herbivory.     

Direct effects of a biocontrol agent are greater than indirect effects through flower visitors for the alien plant Dalmatian toadflax (Linaria dalmatica: Scrophulariaceae)

Herbivory and pollination are important determinants of female reproductive success in flowering plants. Plants must interact with herbivores and flower visitors simultaneously and interaction with one may alter the outcome of the interaction with the other. These indirect effects can have dramatic impacts on plant fitness. The purpose of this study was to examine whether the stem-boring weevil Mecinus janthiniformis (Curculionidae: Coleoptera) affects flower visitation rate and seed set of the exotic plant Dalmatian toadflax (Linaria dalmatica (L.) Mill. Scrophulariaceae). We compared the flower production, flower morphology, visitation rate, fruit production, and pollen limitation on Dalmatian toadflax plants with and without larval feeding by M. janthiniformis. Feeding by M. janthiniformis reduced the number of flowers and per plant visitation rate, and there was a significant interaction between herbivory and flower number suggesting that the change in visitation rate was not solely a function of a reduction in flower abundance. Herbivory also had direct negative impacts on the reproductive success of Dalmatian toadflax. Total flower and fruit production decreased by over 30 % in plants attacked by M. janthiniformis. However, plants with M. janthiniformis were not more pollen-limited than those without M. janthiniformis. This suggests that herbivory had primarily direct effects female reproductive success.     

Feeding behavior of bollworm and tobacco budworm (Lepidoptera: Noctuidae) larvae in mixed stands of nontransgenic and transgenic cotton expressing an insecticidal protein

Feeding behavior of third-instar bollworm, Helicoverpa zea (Boddie), and tobacco budworm, Heliothis virescens (F.), was observed in pure and mixed stands of nontransgenic and transgenic cotton (BTK), Gossypium hirsutum L., expressing an insecticidal protein CryIA(c) from a bacterium, Bacillus thuringiensis Berliner subsp. kurstaki. Five plant stands composed of BTK and non-BTK plants were evaluated; two pure stands and three mixed stands. Percentage ratios of BTK to non-BTK plants in the stands were 100:0, 75:25, 50:50, 25:75 and 0:100, respectively. In all stands with BTK plants, fewer bollworm and tobacco budworm larvae were found on BTK plants than non-BTK plants 24 h after infestation with third instars. At 48 h, significantly fewer tobacco budworm larvae, but not fewer bollworm larvae, were found on BTK plants. However, the number of larvae of either insect did not increase on non-BTK plants compared with the initial infestation density of three larvae per plant. The number of obacco budworm injured flower buds, and capsules was lower in all plant stands containing BTK plants compared with the pure stand of non-BTK at 48 h after infestation. Higher numbers of larvae on non-BTK plants were possibly the result of larval intoxication, reduced feeding, and increased plant abandonment and death on BTK plants rather than a classical feeding preference. Unexpectedly, the number of flower buds and capsules injured by bollworm and tobacco budworm when averaged per plant for all plants in a stand, differed little among the 75:25, 50:50 and 25:75 plant mixtures. These data suggest that larvae of both species frequently moved among plants, feeding indiscriminately on BTK and non-BTK plants.     

Experimental defoliation affects male but not female reproductive performance of the tropical monoecious plant Croton suberosus (Euphorbiaceae)

Background and Aims

Monoecious plants have the capacity to allocate resources separately to male and female functions more easily than hermaphrodites. This can be advantageous against environmental stresses such as leaf herbivory. However, studies showing effects of herbivory on male and female functions and on the interaction with the plant''s pollinators are limited, particularly in tropical plants. Here, the effects of experimental defoliation were examined in the monoecious shrub Croton suberosus (Euphorbiaceae), a wasp-pollinated species from a Mexican tropical dry forest.

Methods

Three defoliation treatments were applied: 0 % (control), 25 % (low) or 75 % (high) of plant leaf area removed. Vegetative (production of new leaves) and reproductive (pistillate and staminate flower production, pollen viability, nectar production, fruit set, and seed set) performance variables, and the abundance and activity of floral visitors were examined.

Key Results

Defoliated plants overcompensated for tissue loss by producing more new leaves than control plants. Production of staminate flowers gradually decreased with increasing defoliation and the floral sex ratio (staminate : pistillate flowers) was drastically reduced in high-defoliation plants. In contrast, female reproductive performance (pistillate flower production, fruit set and seed set) and pollinator visitation and abundance were not impacted by defoliation.

Conclusions

The asymmetrical effects of defoliation on male and female traits of C. suberosus may be due to the temporal and spatial flexibility in the allocation of resources deployed by monoecious plants. We posit that this helps to maintain the plant''s pollination success in the face of leaf herbivory stress.     

Flowering phenology and female fitness: impact of a pre-dispersal seed predator on a sexually polymorphic species

In order to produce seeds, animal-pollinated plants must flower synchronously with and be attractive to their pollinators while avoiding antagonists. Here, we explore temporal and inter-individual patterns in pollination and pre-dispersal seed predation of Dianthus sylvestris by Hadena moths, within and among three sex morphs. We scored plants that started flowering at different periods in 2001 and 2003 and found that fruit set decreased and predation rates increased over one season, and most of the other season, granting a female reproductive advantage to early flowering plants, though, we found no morph-specific temporal patterns. Female plants set more fruits, and more of their fruits escaped predation in one year, but this did not grant them a reproductive advantage since they produce fewer flowers per plant than the other morphs. Instead, mixed plants showed a clear female reproductive advantage. We also examined predation types by Hadena and seed production in attacked and intact fruits of individually marked flowers. Though female Hadena moths laid eggs preferentially into perfect flowers, flower sexes suffered similar predation by itinerant caterpillars. Attacked fruits contained fewer and lighter seeds than un-attacked ones. We conclude that pre-dispersal seed predation by Hadena may select on flowering onset of this sexually polymorphic species.     

Can plants mediate the humoral immunity and biochemical metabolism of entomopathogen‐infected caterpillars?

Plant‐insect herbivore‐entomopathogen interactions are one of the hot topics in biological control and humoral immunity, and biochemical metabolism are important responses of herbivores to pathogen infection. Entomopathogens are key biocontrol agents of caterpillars, but how plants affect the responses of caterpillars to these organisms is not well understood. We studied hormonal immunity (lysozyme and phenoloxidase activities) and biochemical metabolism (total protein and lipid contents) of Beauveria bassiana‐infected beet armyworm (Spodoptera exigua) larvae that feed on five different host plants (soya bean, Chinese cabbage, edible amaranth, water convolvulus and pepper). Results indicated that plant species differentially affected lysozyme and phenoloxidase activity and lipid content, but had no effect on protein content of pathogen‐infected caterpillars. Both lysozyme and phenoloxidase activities were generally higher in entomopathogen‐infected larvae that feed on edible amaranth or water convolvulus compared with the other three plants from days 1 to 5 after treatment. Plant species did not affect in regular changes during the 5 days in the lipid content of infected or non‐infected caterpillars. Our study reveals that plants fail to affect the biochemical metabolism but plants can mediate the humoral immunity of caterpillars to defend against pathogens. This study provides insight into plant‐mediated effects on the response of herbivores to pathogens.