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.     

Effect of black bean aphid, Aphis fabae, on transpiration, stomatal conductance and crude protein content of faba bean

This study was initiated to investigate effects of damage by 0, 5 and 10 aphids/plant on the physiology of faba bean plants throughout different feeding periods and at two plant development stages. Immediately following removal of Aphis fabae, measurements showed 84–229% increase in transpiration rate. These changes were proportional to the number of aphids and infestation duration. Injury by A. fabae caused the stomatal conductance to be much higher in the leaves of infested plants. Leaf stomatal conductance of the infested plants increased significantly by 51–224% depending on initial aphid densities and feeding intervals. This increase was proportional to the infestation level for each date. Length of infestation period and plant growth stage seemed to have no clear effect on stomatal apertures. Aphid feeding caused a damage of about 7–33% of crude protein levels in the leaf tissue. This reduction increased with increasing infestation levels and time, except for 28‐day‐old plants on 28 days. The physiological effects of aphid feeding on water vapour and chemical composition of damaged leaves are particularly serious when the population is high.     

Scab disease of cowpea (Vigna unguiculata) caused by Sphaceloma a species of the fungus

Scab disease of cowpea (Vigna unguiculuta) was shown to be caused by Sphaceloma sp. It affects all above ground parts of the plant. The first symptom of the disease, appearing within 3 to 6 days of inoculation, is puckering of the lamina. Spots on mature leaves are white with or without brown margins. Typical scab lesions on petiole, stem, peduncle and pod are white turning dark brown when chlamydospores are formed and are oblong-elongate except for pod lesions that are ovoid. The most destructive phase is scab of the flowering axis which causes flower and, or, pod abortion or completely prevents flower formation. Inoculation of asparagus pea (V. sesquipedalis) with a cowpea isolate of Sphaceloma sp. produced symptoms similar to those on cowpea. Inoculated hyacinth bean (Lablab niger) produced atypical mild lesions. The following legumes were not affected when artificially inoculated with the fungus: black gram (Phaseolus mungo), green gram (P, aureus), French bean (P. vulgaris), Lima bean (P. lunatus), groundnut (Arachis hypogaea), and soyabean (Glycine max). The characteristics of the fungus on potato dextrose agar are described.     

Leaf epidermal characters related with plant's passive resistance to pathogens vary among accessions of wild beans Phaseolus vulgaris var. aborigineus (Leguminosae–Phaseoleae)

We report here whether accessions of Phaseolus vulgaris var. aborigineus, collected from the southernmost part of the Andean domestication center of common bean, presented differences among leaf epidermal characters. Epidermal microcharacters such as deposition of wax crystalloids, cuticle thickness, trichome types, size and density, stomata types and size, stomatal density and index were examined on the surface of 66 leaves of 11 accessions of P. vulgaris var. aborigineus by means of light and scanning electron microscopy. Unlike the leaves of cultivated beans, those of P. vulgaris var. aborigineus were hypostomatous. Among epidermal characters only the stomatal density, stomatal index, and the number of trichomes on the abaxial leaf epidermis were different between bean accessions. The stomatal density and index of the accessions were inversely related to the altitude of the area of the wild bean collection. This is the first report describing the presence of diversity among epidermal characters (e.g. hypostomatous leaves) in P. vulgaris var. aborigineus that might contribute to plant resistance to pathogens.     

Responses of ethylene biosynthesis to saline stress in seedlings of eight plant species

The effect of salinity (100 mM NaCl) on ethylene metabolism in the early phase of vegetative development of several plant species has been investigated. The effects of saline treatment on shoot and root growth, ranged in sensitivity with respect to species: pepper (Capsicum annum L. cv Pairal) > tomato (Lycopersicon esculentum Mill. cv Malpica) > broccoli (Brassica oleraceae L. var. Italica Plenk. cv Marathon F1) ≅ lettuce (Lactuca sativa var. longifolia Lam. cv Inverna) ≅ melon (Cucumis melo L. cv Ruano F1, Roche type) > bean (Phaseolus vulgaris L. cv. Gator Green 15) ≅ spinach (Spinacia oleracea L. cv Boeing) > beetroot (Beta vulgaris L. var. crassa (Alef.) J. Helm. cv Detroit). After saline treatment, ethylene production increased 4.2-fold in pepper shoots. Significant increases were also found in shoots of tomato, broccoli and bean. In contrast, salinity decreased shoot ethylene production rate in melon, spinach, and beetroot. In roots, the general effect of salinity was a decrease in ethylene production, especially in broccoli and bean, except in tomato root, in which a sharp increase in ethylene production occurred. In general, saline treatment increased total ACC concentration in both shoot and root in most of the plant species examined, which was related to plant sensitivity to salinity. For example, pepper shoot was the most sensitive to saline treatment, showing the highest fresh weight inhibition and the highest increase in total ACC concentration (8.5-fold), while, beetroot was less affected by salinity and showed no effect on total ACC concentration in response to saline treatment.     

In situ hybridization to metaphase chromosomes in six species ofPhaseolus andVigna using ribosomal DNA as the probe

In situ hybridization with a biotin-labeled rice ribosomal DNA (rDNA) probe to the somatic metaphase chromosomes of six species ofPhaseolus andVigna (P. angularis, P. calcaratus, P. coccineus, P. vulgaris, V. sesquipedalis andV. sinensis) was done to determine the sites of rDNA. Hybridization signals were present in the terminal and subterminal chromosome regions of each of the six species. The number of rDNA sites was two inP. angularis andP. calcaratus, four inP. coccineus andP. vulgaris, and six inV. sesquipedalis andV. sinensis.     

Glandular trichomes as an inflorescence defence mechanism against insect herbivores in Iberian columbines

Glandular trichomes play a defensive role against herbivores in the leaves of many plant species. However, their functional role in inflorescences has not been studied, even though theory suggests that tissues with a higher fitness value, such as inflorescences, should be better defended. Using manipulative experiments, we analysed the defensive role of glandular trichomes against herbivorous insects in the inflorescence of Iberian columbines (genus Aquilegia), and its inter-population and inter-taxa variation in relation to herbivore abundance and potential selective pressure. The experiments were conducted in eight populations belonging to four subspecies of two columbines (Aquilegia vulgaris and Aquilegia pyrenaica). For each population, we estimated the density of glandular trichomes in the inflorescences, the abundance of insects stuck in the inflorescences, the abundance of small herbivorous insects, the incidence of damage on flowers and fruits, and the fruit set. The density of glandular trichomes on the inflorescence of A. vulgaris and A. pyrenaica was higher in regions of higher herbivore abundance. We also found that when the plants lose the protection of glandular trichomes, small insects have better access to flowers and fruits, causing more damage and reducing plant fitness. This study concludes that glandular trichomes are part of an adaptive response against phytophagous insect herbivory. The observed variation in herbivore pressure between taxa, likely caused by habitat differentiation, might have played a role in trait differentiation through divergent selection. This result adds evidence to the differentiation of the Iberian columbines through habitat specialization.     

Life history of western flower thrips, Frankliniella occidentalis (Thysan., Thripae), on five different vegetable leaves

Biological characteristics of western flower thrips, Frankliniella occidentalis (Pergande) (Thysan., Thripae), were investigated on excised leaves of five vegetables: cabbage (Brassica oleracea L. var. Jingfeng 1), cucumber (Cucumis sativus L. var. Zhongnong 8), capsicum (Capsicum annuum L. var. Zhongjiao 5), kidney bean (Phaseolus vulgaris L. var. Gonggeizhe) and tomato (Lycopersicon esculentum M. var. zhongza 9). The developmental time from egg to adult on the cucumber, cabbage, bean, capsicum and tomato leaf was 9.22 ± 0.13, 10.19 ± 0.08, 10.42 ± 0.06, 12.15 ± 0.07 and 12.91 ± 0.04 days, respectively. Survivorship of immatures on cucumber, cabbage and tomato was high (75–80%) but low on capsicum (50%). The total number of first instars produced was highest on cabbage (76.62 ± 11.79), while the daily first instar production was highest on cucumber (6.12 ± 1.81), whereas the total and daily first instar production rates were lowest on capsicum (7.67 ± 3.35 and 1.89 ± 0.91). F. occidentalis had the highest intrinsic rate of increase (r_m) on cucumber (0.208), followed by cabbage (0.184), bean (0.164), tomato (0.100) and capsicum (0.017). The results indicate that cucumber was the most suitable host plant for F. occidentalis, whereas capsicum was the least suitable.     

Plant species variation in bottom‐up effects across three trophic levels: a test of traits and mechanisms

1. An increasing number of studies have addressed the mechanisms by which plant inter‐specific variation influence interactions at higher trophic levels, but little is known about the underlying plant traits driving these dynamics. 2. Here we investigated the effects of host plant species on herbivore‐parasitoid interactions and the underlying traits driving such effects. For this, we measured the abundance of seed‐eating bruchids and their parasitoids across seven sympatric populations of the bean species Phaseolus coccineus and Phaseolus vulgaris in Central Mexico. To investigate the mechanisms underlying differences between bean species in bruchid‐parasitoid interactions, we carried out two laboratory experiments to test whether bruchid and parasitoid performance differed between plant species. We also measured seed size and phenolic compounds to investigate if seed traits mediate bruchid‐parasitoid interactions by influencing herbivore susceptibility or resistance to parasitoids. 3. Field surveys revealed that the rate of parasitoid recruitment to bruchids was significantly higher on P. vulgaris than on P. coccineus. Subsequent laboratory bioassays indicated that bruchids developed more slowly and exhibited lower fitness on P. vulgaris seeds than on P. coccineus seeds. Accordingly, we found that bean species differed in seed size, with P. vulgaris having smaller (less nutritious) seeds, which explains why bruchid development was slower on this plant species. 4. These results provide a mechanism for why bruchids exhibited higher parasitism rates on seeds of P. vulgaris in the field which could be due to Slow‐Growth/High‐Mortality effects, a smaller physical refuge provided by the seed, or both factors. The roles of these mechanisms remain inconclusive without further study.     

Studies of the infection of the winged bean by Synchytrium psophocarpi in Papua New Guinea

Infection of leaves and stems of Psophocarpus tetragonolobus by Synchytrium psophocarpi only occurred following spray inoculation of motile zoospore suspensions and incubation for a minimum of 12 h in polyethylene bags or a mist chamber. The incubation period was 7 days and generation time 22 days at temperatures of 31 ^oC max, 24 ^oC min and r.h. of 90% max, 70% min. Young, 1–2 day-old leaves were most susceptible; there was no infection on 10 day-old leaves and susceptibility was not increased by the removal of leaf waxes. No infection occurred when plants were grown from seed from infected pods, seed inoculated with zoospores or sporangia and seed sown in soil containing infected leaf debris. Resting spores were not found in infected tissues stored for 12 wk or in plant debris. S. psophocarpi did not infect Arachis hypogaea, Glycine max, Phaseolus aureus, P. coccineus, P. vulgaris, Pisum sativum, Psophocarpus scandens, Vicia faba, Vigna sesquipedalis and V. unguiculata. S. minutum did not infect winged bean. Inoculation confirmed the susceptibility of the winged bean lines UPS 62, UPS 122, UPS 126 and resistance of two Thai winged bean lines 1602/1 and 1611/2.     

Enzyme inhibitors from plants: Enterokinase inhibitors in tubers and seeds

Of the 22 tubers and 9 pulses screened for inhibitors of enterokinase activity, the following 12 tubers,Curcuma amada, Kyllinga monocephala, Solanum tuberosum, Canna indica, Helianthus tuberosus, Coleus parviformis, Mirabilis jalapa, Colocasia antiquorum (red variety),Alium cepa, Amorphophalus companulatus, Maranta arundinacea, Daucus carota, and 9 pulses namely,Vigna sinensis, Arachis hypogea, Pisum sativum, Phaseolus vulgaris (white bean),Phaseolus vulgaris (kidney bean),Phaseolus mungo, Cicer arietinum, Dolichos lablab and Cajonus cajan contained inhibitory activity. Three tubers,Amorphophalus companulatus, Maranta arundinacea andDaucus carota and all the nine pulses exhibited endogenous esterase activity towards benzoyl arginine ethyl ester. Among the 8 pulses and 3 tubers processed by affinity chromatography on trypsin-sepharose, to separate trypsin inhibitor from enterokinase inhibitor,Phaseolus vulgaris (kidney bean),Phaseolus vulgaris (white bean) andDolichos lablab contained distinct enterokinase inhibitors. These fractions were devoid of trypsin inhibitor activity. The trypsin inhibitor fromColeus parviformis tubers alone did not bind to trypsinsepharose and was recovered in the unbound fraction along with the enterokinase inhibitor.     

Evaluation of induced responses, insect population growth, and host-plant fitness may change the outcome of tests of the preference-performance hypothesis: a case study

The preference‐performance hypothesis predicts that insect preference should correspond to host suitability for offspring development. We studied the pattern of within‐plant preference in the aphid Sipha flava and its consequences for offspring performance on the host‐plant Sorghum halepense, regarding the role of induced responses of plants to aphid feeding. The consequences of within‐plant preference on aphid population growth and host‐plant traits were also evaluated. Our results showed that winged and wingless aphids preferred to settle on mature rather than young leaves. In contrast, aphid individual growth rate was higher on young leaves when compared with mature leaves, suggesting that the outcome of this test rejected the preference‐performance hypothesis. However, the inclusion of the factor ‘previous aphid infestation’ changed the outcome from a maladaptive choice to a neutral one. Thus, individual growth rates of S. flava increased when aphids developed on leaves that had been previously infested. Interestingly, aphid growth rate on previously infested leaves did not differ between young and mature leaves. On the other hand, aphid population reproductive rate was higher and the percentage of winged aphids lower when infestation occurred on mature rather than young leaves. Aphid infestation reduced plant and shoot biomass, and increased leaf mortality. These negative effects on plant traits related to plant fitness were greater when aphid infestation occurred on young leaves. Likewise, whereas infestation on mature leaves did not cause a significant reduction in the number of flowering plants compared with control plants, aphid infestation on young leaves did reduce the number of plants at the flowering stage. Consequently, if both the reproductive rate of aphids in the mid‐term, and host‐plant fitness are taken into account, the results indicate that aphid preference for mature leaves may be an adaptive choice, thus supporting the preference‐performance hypothesis.     

Do pollinators influence seed-set in Banksia paludosa Sm. and Banksia spinulosa R. Br.?

The consequences of observed variations in pollinator activity for plant reproduction depend on the breeding system of the plant and also on whether pollination is a resource in short supply. These factors are frequently assumed rather than tested. In bagging experiments with Banksia paludosa in heath and B. spinulosa var. spinulosa in woodland, the present study demonstrated that seed-set does not occur by autogamy and that pollinators are indeed necessary. Experimental addition of outcrossed pollen to inflorescences failed to produce any increase in the mean number of seeds per inflorescence, measured for non-barren inflorescences, for either species. However, in B. paludosa, the addition of pollen increased the numbers of inflorescences that set seed from 20% (controls) to 45% (pollen-added treatment). This suggests either unusual patterns of pollen movement among and within plants or control of the pattern of seed-set within a plant. Pollen additions failed to alter seed-set in B. spinulosa. It is possible that a greater abundance of pollinators in the woodland ensures adequate pollination for these plants     

种植茼蒿对蚕豆苜蓿蚜的田间控制作用

[目的] 探讨不同生育期和不同种植方式的茼蒿对蚕豆蚜虫的诱集作用,为利用茼蒿控制蚕豆蚜虫提供理论依据。[方法] 在蚕豆田四周种植不同生育期（幼苗期、现蕾期、开花期）和不同行数（1行、2行）的茼蒿,观察不同处理的蚕豆田有蚜株率和蚜害等级,各处理设在互不干扰的小区内进行。[结果] 蚕豆四周种植不同生育期茼蒿后,蚕豆上有蚜株率和蚜害等级比例存在显著差异,且与茼蒿的生育期有明显的相关性,各处理有蚜株率从低到高分别为茼蒿开花期（28.33%） < 现蕾期（41.67%） < 幼苗期（55.00%）,并均显著低于对照（63.33%）;种植不同生育期茼蒿后,各处理蚕豆蚜害等级也不同,5级蚜害在种植开花期茼蒿处理后仅为5.00%,现蕾期为23.33%,幼苗期为33.33%,对照蚕豆上蚜害最高,达40.00%。分别种植1行（33.33%）和2行（23.33%）茼蒿后,最高有蚜株率均显著低于对照（66.67%）,低蚜害等级比例明显增高,高蚜害比例明显下降,且种植2行的效果更佳。[结论] 开花期的茼蒿对蚕豆蚜虫诱集作用最强,种植2行开花期茼蒿可以有效降低蚕豆蚜虫为害。在蚕豆生产上,种植茼蒿可以作为蚕豆蚜虫生态防控的重要手段之一。     

Tunisian isolates of Trichoderma spp. and Bacillus subtilis can control Botrytis fabae on faba bean

Faba bean crops worldwide are often attacked by different diseases, particularly chocolate spot caused by Botrytis fabae Sard. Fungal and bacterial isolates collected from faba bean and barley leaves in Tunisia were evaluated for their antagonistic potential against B. fabae. In a test on detached leaves, the highest rate of decrease in disease severity was scored by Trichoderma viride, followed by T. harzianum, the fungicide Carbendazim then Bacillus subtilis. Under glasshouse conditions, all tested fungi resulted in significant disease severity reduction. T. viride reduced the rate of chocolate spot infestation on leaves and stems by 35% and 31.5%, respectively, when the rate on the control was 100%. For T. harzianum, Carbendazim and B. Subtilis, the rates of infestation on the leaves were 41.7%, 43.1% and 59.7%, respectively. On the stems, T. harzianum scored the lowest rate of 54.2% followed by B. subtilis with 79.2% then Carbendazim with 87.5%. Two consecutive seasons of field trials using the Trichoderma species, B. subtilis and Carbendazim showed significant and consistent reduction in the severity of chocolate spot infestation rates. The highest protection against the disease was obtained from T. viride. Based on these results, Tunisian isolates of Trichoderma spp. can be recommended for developing commercial bio-fungicides for integrated management of chocolate spot.     

The interaction between host and host plant influences the oviposition and performance of a generalist ectoparasitoid

The successful development of parasitoids of herbivores depends on the quality of their host, which is often affected by the host plant. Therefore, a parasitoid’s oviposition decisions will directly depend on the host, but also on plant quality. Here, we investigated the direct effects of host species and the indirect effects of the host’s food plant on the oviposition decisions and performance of the gregarious ectoparasitoid Euplectrus platyhypenae Howard (Hymenoptera: Eulophidae). With a series of no‐choice experiments, we determined the oviposition and performance of the parasitoid on: (1) two caterpillar species, fall armyworm, Spodoptera frugiperda JE Smith (Lepidoptera: Noctuidae), and velvet armyworm, Spodoptera latifascia Walker, reared on maize (Zea mays L., Poaceae), (2) the same caterpillars reared on maize, bean (Phaseolus vulgaris L., Fabaceae), or squash (Cucurbita pepo L., Cucurbitaceae) leaves, and (3) S. latifascia caterpillars reared on leaves of wild and cultivated lima bean, Phaseolus lunatus L. All these insects and plants originate from Mesoamerica where they have coexisted for thousands of years in the traditional agricultural system known as Milpa in which maize, beans, and squash are planted together. We found that the preferred and best combination of host and host plant for parasitoid performance was S. frugiperda on maize. Parasitoids laid larger clutches, had higher survival, and more females and larger adults emerged from S. frugiperda reared on maize. However, when both caterpillar species were reared on squash, S. latifascia was the better host. Contrary to the literature, S. frugiperda was not able to develop on bean plants. Results from the lima bean experiment showed that parasitoid performance was best when S. latifascia was reared on leaves of cultivated compared to wild lima bean. These findings are discussed in the context of mixed cropping in which the ability of generalist parasitoids to switch among hosts and host plant species could be advantageous for pest management.     

Feeding ecology of the vulnerable aoudad (Ammotragus lervia) in north-western Sahara

The feeding ecology of the aoudad (Ammotragus lervia) was investigated for the first time in north-western Sahara, Djebel Antar (Bechar province, Algeria), from autumn 2015 to summer 2016. Microhistological analyses of faeces revealed an annual diet composed of 23 identified taxa belonging to 16 plant families. The highest species diversity was recorded in spring and summer (23 species), despite a marked consumption of two species: Vachellia tortilis (17.7%) and Avena sterilis (14.0%); diet diversity was lower in autumn and winter (16 species), including mainly Teucrium polium (14.7%, 21.0%) and Gymnocarpos decander (19.7%, 10.0%). The main plant parts consumed during these seasons were stems (77.7%, 65.3%), while leaves and inflorescences were mostly consumed during spring and summer (54.7%, 52.3%). Forbs dominated the aoudad's diet, with 46.3% average relative abundance, including mainly T. polium, Limoniastrum feei, and Chrysanthemum macrocarpum. Woody plants including mainly V. tortilis and G. decander accounted for 33.3% (50.0% in autumn), and grasses including A. sterilis and H. murinum for 20.4% (32.0% in summer). Based on this diet, A. lervia can be classified as a “generalist mixed-feeder.”     

Variation in the phenology and abundance of flowering by native and exotic plants in subalpine meadows

The timing and abundance of flower production is important to the reproductive success of angiosperms as well as pollinators and floral and seed herbivores. Exotic plants often compete with native plants for space and limiting resources, potentially altering community floral dynamics. We used observations and a biomass-removal experiment to explore the effects of an invasive exotic flowering plant, Linaria vulgaris, on community and individual species flowering phenology and abundance in subalpine meadows in Colorado, USA. Invasion by L. vulgaris was associated with a shift in both the timing and abundance of community flowering. Invaded plant communities exhibited depressed flowering by 67% early in the season relative to uninvaded communities, but invaded sites produced 7.6 times more flowers than uninvaded sites once L. vulgaris began flowering. This increase in flowers at the end of the season was driven primarily by prolific flowering of L. vulgaris. We also found lower richness and evenness of resident flowering species in invaded plots during the period of L. vulgaris flowering. At the species level, a common native species (Potentilla pulcherrima) produced 71% fewer flowers in invaded relative to uninvaded plots, and the species had reduced duration of flowering in invaded relative to uninvaded sites. This result suggests that L. vulgaris does not simply alter the flowering of subordinate species but also the flowering of an individual common species in the plant community. We then used observational data to explore the relationship between L. vulgaris density and resident floral production but found only partial evidence that higher densities of L. vulgaris were associated with stronger effects on resident floral production. Taken together, results suggest that a dominant invasive plant can affect community and individual-species flowering.     

Stem borer's species composition,abundance and infestation on maize and millet in Maiduguri,Nigeria

The species composition, abundance and plant infestation of stem borers attacking maize and millet were investigated in farmers' fields during the cropping season of 2010 and 2011 in Maiduguri, Nigeria. Stem borers were collected via destructive sampling. In total, three stem borer species (Busseola fusca, Sesamia calamistis and Coniesta ignefusalis) were found, of which S. calamistis (64%) and C. ignefusalis (72%), respectively, were predominant on maize and millet. Across both years, whereas mean plant infestation ranged from 4.8% on millet to 20.8% on maize, mean stem borer abundance ranged from 1.6 individuals on millet to 13.8 individuals on maize. Mean total plant infestation and stem borer abundance varied with different years and both were significantly higher during the 2010 than 2011 cropping season. In spite of the generally low stem borer abundance per farmers' field, plant infestation particularly on maize plants seems to be moderate during different years.     

Community‐wide impact of an exotic aphid on introduced tall goldenrod

1. The aphid Uroleucon nigrotuberculatum Olive, which is specialised to the tall goldenrod, Solidago altissima L., in its native range, has become a dominant species on the introduced tall goldenrod in Japan. How this exotic aphid influenced arthropod communities on the introduced tall goldenrod in aphid‐present (spring) and aphid‐absent (autumn) seasons was examined, using an aphid removal experiment. 2. In spring, aphid presence increased ant abundance because aphid honeydew attracted foraging ant workers. A significant negative correlation was found between the numbers of ants and herbivorous insects other than aphids on the aphid‐exposed plants, but no significant correlation was detected on the aphid‐free plants. Thus, the aphid presence was likely to decrease the abundance of co‐occurring herbivorous insects through removal behaviour of the aphid‐tending ants. There were no significant differences in plant traits between the aphid‐exposed and aphid‐free plants. 3. In autumn, the numbers of lateral shoots and leaves, and the leaf nitrogen content were increased in response to the aphid infestation in spring. Because of the improvement of plant traits by aphid feeding, the abundance of leaf chewers increased on aphid‐exposed plants. In contrast, the abundance of sap feeders decreased on the aphid‐exposed plants. In particular, the dominant scale insect among sap feeders, Parasaissetia nigra Nietner, decreased, followed by a decrease in the abundance of ants attending P. nigra. Thus, aphid feeding may have attenuated the negative impacts of the tending ants on leaf chewers. 4. Aphid presence did not change herbivore species richness but changed the relative density of dominant herbivores, resulting in community‐wide effects on co‐occurring herbivores through ant‐mediated indirect effects, and on temporally separated herbivores through plant‐ and ant‐mediated indirect effects. The aphid also altered predator community composition by increasing and decreasing the relative abundance of aphid‐tending ants in the spring and autumn, respectively.