Extraction from soil of apterous Pemphigus populitransversus (Hemiptera: Pemphigidae) feeding on cruciferous vegetable roots

The poplar petiolegall aphid, Pemphigus populitransversus Riley (Hemiptera: Pemphigidae), is a gall-forming aphid attacking leaf petioles of Populus spp., its primary hosts. Its secondary hosts are the roots of cruciferous (Brassicaceae) plants, where it is also commonly known as the "cabbage root aphid." The apterous forms are destructive pests of cruciferous vegetables in many parts of the world. In our experiments, the root-feeding apterous forms were extracted from the soil using a Berlese funnel, which drives the aphids downward by using light and heat. The results show that a majority of apterous aphids (96.9%) were extracted from the soil in 2 h by using a 15-W light bulb in the Berlese funnels, whereas only 18.2% of aphids were extracted using a 25-W light bulb in a similar time period. The 25-W light bulb in the funnel generated too much heat (40-44 degrees C), which dried the soil too fast so that the aphids were unable to crawl downward to the collecting jars or killed the aphids directly. The advantages of using a Berlese funnel equipped with a 15-W light bulb as the light and heat source for sampling and extraction of the root feeding aphids include a uniform handling of each sample, less time spent, extraction of many samples at the same time, and storage of the aphids in containers for later counting in the laboratory. This technique seems to also be useful for extracting other mobile, small soil-dwelling arthropods.     

The cost of conflict in aphid societies

Most social aphids are found within plant galls, inside of which clonally‐derived family groups feed, and specialized larval castes forego reproduction and perform various cooperative tasks, including group defence. When unrelated aphids move between clones, conditions are ripe for conflict because galls and cooperative defence are shared resources that are vulnerable to exploitation. A key unknown is whether conflict is costly in aphid social groups. We show that diversity within groups is negatively correlated with performance in the North American social aphid, Pemphigus obesinymphae. A substantial fraction of productivity is invested into drifting. However, drifting aphids tend to mature and depart non‐natal galls prior to the seasonal peak in fecundity. These results suggest that when unrelated individuals move between groups, social aphids may experience conditions consistent with a tragedy of the commons. These results also emphasize the strongly convergent properties associated with conflict across the spectrum of animal and microbial sociality.     

Detection of fungal metabolites of various Trichoderma species by the aphid Schizaphis graminum

The feeding preferences of alate and apterous morphs of the aphid Schizaphis graminum (Rondani) (Homoptera: Aphididae) were evaluated using leaves treated with powdered rice cultures of four fungal isolates belonging to different species of the genus Trichoderma (Deuteromycotina: Hyphomycetes). All of the fungal isolates restrained alate morphs of S. graminum from visiting treated leaves, but only Trichoderma citrinoviride Bisset also influenced the preference of apterous morphs. Trials carried out with supernatants obtained by centrifuging aqueous suspensions of the fungal cultures showed that the feeding preference of aphids was maintained in the absence of fungal spores and mycelia, supporting the hypothesis that at least part of the fungal metabolites responsible for this effect were water‐soluble compounds. Electrophysiological studies showed that the structures involved in the perception of the fungal metabolites are located on the aphid tarsomeres.     

Occurrence of entomopathogenic fungi in migratory alate aphids in Yunnan Province of China

Occurrence of entomopathogenic fungi in migratory alate aphids was investigated by trapping air-borne aphids on cabbage and wheat plants and observing the insects for fungal infection. Potted cabbage and wheat plants put 30 m apart on yellow cloth, were placed on the top of a tall building (six-story building) in Yunnan Province, China away from cultivated fields or other vegetation. Seven species of aphids trapped on the plants collected and monitored for fungal infection in the laboratory at a daily basis from 19 February to 31 December, 2003. Aphids were trapped every day during the experimental period. A total of 3,681 aphids were trapped on cabbage and 3,028 on wheat. Myzus persicae (Sulzer), Brevicoryne brassicae (L.), and Sitobion avenae (F.) were the major aphid species accounting for 94.7 and 93.1% of the insect specimens landing on cabbage and wheat, respectively. Other aphis species encountered included, Acyrthosiphon pisum (Harris), Lipaphis erysimi (Kaltenbach), Pemphigus sinobursaris Zhang, and Rhopalosiphum padi (L.). Preference for host plant played significant role in attraction of aphids, especially of the three major species. Accumulated over the whole experimental period nearly 33% of the aphids landing on cabbage and 37% landing on wheat were infected with fungi. Erynia neoaphidis Remaudiere and Hennebert, Entomophthora planchoniana Cornu, and Beauveria bassiana (Balsamo) Vuilemin were the major fungal pathogens encountered and accounted for nearly 95% of the infested aphids on cabbage and 97% on wheat. Other entomopathogenic fungi encountered included Zoophthora radicans (Brefeld) Batko, Conidiobolus obscurus (Hall and Dunn) Remaudiere, and Neozygites fresenii (Nowakowski), Paecilomyces fumosoroseus (Wize) Brown and Smith, and Aspergillus flavus Link. Although the number of aphids trapped throughout the experimental period did not vary consistently with temperature or humidity, the fungal was directly related to relative humidity. Higher insect mortality, especially due to Entomophthorales, positively related relative humidity.     

3种寄主上桃蚜的选择性及形态分化

桃蚜是一种重要的农业害虫,寄主广泛,种下分化复杂。以采自黄土高原旱作区桃树、烟草、甘蓝上的桃蚜为研究对象,通过叶片选择法、传统比较形态测定法研究了3种寄主上桃蚜的选择性及形态分化。结果表明:在3种寄主同时存在的情况下,烟草上的桃蚜嗜食烟草,表现为63.5%的桃蚜选择烟草叶,13.8%选择甘蓝叶,8.2%选择桃叶,而甘蓝和桃树上的桃蚜对原寄主没有表现出明显的嗜好性;从形态指标来看,3种寄主上的桃蚜在体长、触角末节长度、后足腿节长度、触角与体长的比例方面存在显著差异(P0.05),说明这几个特征可以作为区分这3种寄主上桃蚜的依据。综合分析可以初步认为黄土高原旱作区烟草上的桃蚜可能形成了寄主专化型-烟草型。     

Differential inter- and intra-specific defense induction in Lupinus by Myzus persicae feeding

Experiments were conducted to investigate the potential induction of plant defenses by Myzus persicae Sulzer (Homoptera: Aphididae) feeding on five lupin, Lupinus spp. (Leguminosae), varieties with well‐characterized levels of aphid resistance. Myzus persicae feeding on L. angustifolius and L. luteus varieties induced genotype‐specific changes in their host that were not consistent with the level of aphid resistance or the plant species. The plant responses were systemically detected by apterous and alate forms of the aphids. Chemical assays revealed no induction of oxidizing enzyme (catalase, peroxidase, or polyphenol oxidase) activity, serine or cystein proteinase inhibitors, or soluble phenolics in any of the five varieties tested following 3 days of feeding by 10 or 30 aphids. However, there were significant differences among the five lupin varieties in the levels of peroxidase and polyphenol oxidase activity, proteinase inhibitors, and soluble phenolics.     

UV‐B impact on aphid performance mediated by plant quality and plant changes induced by aphids

Plants face various abiotic and biotic environmental factors and therefore need to adjust their phenotypic traits on several levels. UV‐B radiation is believed to impact herbivorous insects via host plant changes. Plant responses to abiotic challenges (UV‐B radiation) and their interaction with two aphid species were explored in a multifactor approach. Broccoli plants [Brassica oleracea L. convar. botrytis (L.), Brassicaceae] were grown in two differently covered greenhouses, transmitting either 80% (high UV‐B) or 4% (low UV‐B) of ambient UV‐B. Three‐week‐old plants were infested with either specialist cabbage aphids [Brevicoryne brassicae (L.), Sternorrhyncha, Aphididae] or generalist green peach aphids [Myzus persicae (Sulzer), Sternorrhyncha, Aphididae]. Plants grown under high‐UV‐B intensities were smaller and had higher flavonoid concentrations. Furthermore, these plants had reduced cuticular wax coverage, whereas amino acid concentrations of the phloem sap were little influenced by different UV‐B intensities. Cabbage aphids reproduced less on plants grown under high UV‐B than on plants grown under low UV‐B, whereas reproduction of green peach aphids in both plant light sources was equally poor. These results are likely related to the different specialisation‐dependent sensitivities of the two species. The aphids also affected plant chemistry. High numbers of cabbage aphid progeny on low‐UV‐B plants led to decreased indolyl glucosinolate concentrations. The induced change in these glucosinolates may depend on an infestation threshold. UV‐B radiation considerably impacts plant traits and subsequently affects specialist phloem‐feeding aphids, whereas aphid growth forces broccoli to generate specific defence responses.     

Spatio-temporal patterns of mortality in Pemphigus populicaulis and P. populitransversus on cottonwoods

Summary Galls of the aphid species Pemphigus populitransversus and P. populicaulis from a single cottonwood in Clinton, New York were censused for mortality approximately every ten days during the summer of 1978. P. populitransversus had significantly higher survival than P. populicaulis. Both species of aphid showed considerably elevated mortality later in the season. Mortality was not spatially random, but neighboring galls had a tendency to die at close to the same time. This tendency to spatially autocorrelated mortality varied from time to time, being more pronounced earlier in the season than later. Later in the season, galls on the outer portions of branches tended to have a higher mortality rate than galls closer to the main trunk of the tree. This effect was highly significant in P. populicaulis, but only suggestive in P. populitransversus.The proportion of dead galls in samples of the two species taken at other times and places was consistent with the data from the censuses. In addition, the potential of two common predators, Anthocoris sp. and Leucopis sp., for producing autocorrelated mortality in Pemphigus was assessed in these collections. There was some association of Leucopis with regions of higher mortality, but this was not the case in Anthocoris. Leucopis tended to be found in galls of P. populicaulis more frequently than in P. populitransversus unlike Anthocoris, suggesting that some of the differential mortality between P. populitransversus and P. populicaulis might be due to this dipteran predator.     

Behavioral and physiological responses of Diaeretiella rapae to semiochemicals

Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae) parasitizes many aphid species, including cabbage aphids on cruciferous crops and Russian wheat aphids on cereal crops. We investigated the olfactory perception of D. rapae to semiochemicals that may be encountered in these two environments while searching for hosts or for mates. We conducted electroantennogram and flight-tunnel experiments on male and female D. rapae and found marked differences between sexes. Cruciferous volatiles elicited physiological and behavioral responses by females but not by males. Males and females responded similarly to (Z)-3-hexen-1-ol, a component of green-leaf volatiles, in both electroantennogram and flight-tunnel assays. Female wasps responded similarly regardless of prior oviposition experience or population origin. Likewise, mating history and aphid presence did not increase responsiveness toward these semiochemicals.     

Feeding location affects demographic performance of cabbage aphids on winter canola

The cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae), is a perennial pest that specializes on plants of the Brassicaceae family, attacking winter canola (Brassica napus L.) mainly during and after flowering. Under field conditions, cabbage aphid colonizes the upper flowering canopy. Population dynamics of aphids in the flowering canopy could be regulated by differences in either plant quality (bottom‐up) or predatory (top‐down) forces. The goal of our study was to determine the effect of feeding location on cabbage aphid demography. A stage‐structured matrix population model was constructed for aphids restricted to reproductive or vegetative plant tissues of canola. We found that feeding location had a large impact on demography of cabbage aphid; the finite rate of increase (λ ± SEM) was higher when aphids were restricted to reproductive tissues, compared to aphids feeding on vegetative tissues: 1.25 ± 0.01 vs. 1.17 ± 0.01 (leaves). Aphids confined to reproductive tissues with higher λ exhibited shorter generation times (T = 14.2 ± 0.2 days) and 53–75% higher net reproductive rates (R₀ = 23.3 ± 1.7) than aphids feeding on vegetative tissues. Prospective analyses showed that there was a nymph‐skewed stable stage distribution, and elasticity values revealed that λ is most sensitive to changes in stasis of adults staying in the adult stage and to adult survival. Retrospective analyses indicated that variation in adult fecundity (value of 0.05) had the largest effect on population dynamics but collectively, growth of nymphal stage 2–3, 3–4, and 4 to adult accounted for most of the difference in λ between the treatments. Monitoring programs should target adults and penultimate instars colonizing reproductive tissues of canola plants in the field as aphids on these plant structures contribute most to population growth.     

Comparative study of interspecific genetic divergence and phylogenic analysis of genus <Emphasis Type="Italic">Jatropha</Emphasis> by RAPD and AFLP

Genus Jatropha with 172 species having significant economic importance belongs to the family Euphorbiaceae. There are no reports on molecular characterization and phylogenetic relationship among the species of Jatropha. Hence, the present study was undertaken to assess the extent of genetic variability that exist and also to establish phylogenetic relationship among Jatropha curcas, J. glandulifera, J. gossypifolia, J. integerrima, J. multifida, J. podagrica and J. tanjorensis using RAPD and AFLP. The percentage of loci that are polymorphic among the species studied was found to be 97.74% by RAPD and 97.25% by AFLP. The mean percentage of polymorphism (PP) was found to be 68.48 by RAPD and 71.33 by AFLP. The phylogram generated with RAPD and AFLP data showed maximum similarity. With the generated data maximum relatedness was found between J. curcas and J. integerrima this may be the reason for the success of inter hybrid crosses between these two species. Neither RAPD nor AFLP data generated in this study supports the view of J. tanjorensis, a natural interspecific hybrid between J. curcas and J. gossypifolia. The present study concludes that both RAPD and AFLP techniques are comparable in divergence studies of Jatropha species. The markers generated by RAPD and AFLP can be employed efficiently for interspecific hybrids identification, marker assisted selection and genetic resource management.     

Effects of integrating companion cropping and nitrogen application on the performance and infestation of collards by Brevicoryne brassicae

Sustainable management of cabbage aphids, Brevicoryne brassicae (L.) (Hemiptera: Aphididae), is a major goal for collard, Brassica oleracea (L.) var. acephala (Brassicaceae), growers globally. Host finding ability of insect pests is significantly affected by diversified cropping systems, and this approach is being utilized currently as a pest management tool. Soil nutrition and its interaction with the cropping systems could have a significant effect on the general performance of collards and the infestation by cabbage aphids. In a search for a sustainable cabbage aphid control, a two‐season field experiment was carried out with two intercrops, collards and chilli, Capsicum frutescens (L.) (Solanaceae), and collards and spring onions, Allium cepa (L.) (Alliaceae), and a collard monoculture. For each of the cropping systems, nitrogen (N) was applied to the soil as a top‐dress at 20, 25, 30, and 35 g per collard plant. The response factors monitored were collard yield (fresh weight) and aphid infestation on collards. Spring onion‐collard intercrop had the lowest aphid density and the highest yield. Collard monoculture had the highest aphid infestation and the lowest yield. High levels of N led to increased infestation of collards by aphids, but also led to a significant increase in the yield of collards. Significant interactions between the N rates and the cropping systems were observed on some sampling dates, with the highest yield being realized under a combination of spring onion‐collard intercrop at a N rate of 30 g per plant. High aphid density led to a decrease in the yield of collards. It was concluded that with a spring onion‐collard intercrop, the soil N level could be raised from the blanket rate of 20–30 g per plant and this would lead to an increase in yield.     

Macrosiphum on ferns: taxonomy,biology and evolution,including the description of three new species (Hemiptera: Aphididae)

The phytophagous insect fauna of ferns has often been described as depauperate, and some have pointed to the paucity of evidence for adaptive radiation of insect groups feeding specifically on ferns. This paper examines the world's species of fern‐specific Macrosiphum aphids and attempts to determine whether fern‐feeding is a monophyletically derived trait in Macrosiphum. All sixteen species reported to feed on ferns, including three new species, were included in a cladistic analysis, along with fifteen other Macrosiphum species selected to represent the diversity of the genus, Papulaphis sleesmani (Pepper), because of its similarity to fern‐feeding Macrosiphum, and Sitobion avenae (Fabricius), which was used as outgroup. The results gave good support for the monophyly of fifteen of the sixteen fern‐feeders, and also supported a clade consisting of these fifteen fern‐feeders plus Macrosiphum equiseti (Holman), an Equisetum‐specific aphid. One species, Macrosiphum lapponicum Shaposhnikov, from northern Russia, was concluded to be unrelated to other fern‐feeding Macrosiphum. Whether this species truly feeds on a fern requires confirmation. Taxonomic and biological notes are provided for all fern‐feeding Macrosiphum of the world. These include one new combination, Macrosiphum cyatheae (Holman) comb.n., and three new species: Macrosiphum longirostratum sp.n. on Woodsia mollis and Woodsia sp. from Mexico (Michoacán), Macrosiphum miho sp.n. on ‘Aspidium’ sp. from the U.S.A. (Illinois) and Macrosiphum rebecae sp.n. on Adiantum sp. from Mexico (Michoacán). Keys to apterous and alate viviparae of Macrosiphum living on ferns are given.     

The influence of glucosinolates and sugars on feeding by the cabbage stem flea beetle,Psylliodes chrysocephala

Agar was used as an artificial substrate to investigate the feeding behaviour of the cabbage stem flea beetle,Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae), an important pest of winter oilseed rape (Brassica napus) in Europe. Both glucosinolates and sugars stimulated feeding when added to agar. The amount of feeding that occurred was affected by the type and concentration of glucosinolate and surgar and also by combinations of components. Although glucosinolates were potent feeding stimulants forP. chrysocephala, they were not a prerequisite for feeding, nor does it seem likely that glucosinolate profiles are used by this species to discriminate amongst cruciferous plants at the gustatory level.     

Performance of clones and morphs of two cereal aphids on wheat plants with high and low nitrogen content

The great variability of the aphid life cycle and their tendency for host alternation gives rise to aphid clones and morphs. Inter‐ and intraclonal variability may be observed in the responses of aphids to various environmental factors. In this study we aimed to evaluate the influence of intrinsic factors (clone and morph type) on the intrinsic rate of increase (r_m) of the English grain aphid, Sitobion avenae (Fabricius), and the bird cherry‐oat aphid, Rhopalosiphum padi (Linnaeus). For each species four apterous clones were collected from established laboratory colonies and compared to assess their relative fitness on high‐ and low‐nitrogen wheat plants under laboratory conditions. The clones had significantly different intrinsic rates of increase on high‐ and low‐nitrogen plants. All R. padi clones had a higher intrinsic rate of increase and mean relative growth rate than S. avenae. Experiments were also conducted to compare the mean fecundity of apterous and alate morphs of S. avenae and R. padi clones on high‐ and low‐nitrogen wheat plants. On high‐nitrogen plants the apterous morphs of S. avenae clones had significantly higher mean fecundity than alate morphs. There were no significant differences between the mean fecundity of alate morphs of the same species on high‐ and low‐nitrogen plants. The results support the idea of better fitness of specific clones/morphs on certain host plants due to higher and lower intrinsic rates of increase.     

Maternal host plant effects on aphid performance: contrasts between a generalist and a specialist species on Brussels sprout cultivars

• 1 The performance of the second generation (G₂) of alates and apterae of a generalist, Myzus persicae, and a specialist, Brevicoryne brassicae, aphid species reared on Chinese cabbage or cabbage was evaluated on five cultivars of Brussels sprout.
• 2 Aphid performance was influenced both by the type of host on which the parent aphid had been reared and by the host on which it was feeding when reproducing.
• 3 The fecundity of the G₂ of alates of both aphid species reared on Chinese cabbage differed significantly between all the cultivars of Brussels sprout and, on average, was 25% higher than those reared on cabbage. These differences were also apparent for the intrinsic rate of increase of B. brassicae but not for M. persicae.
• 4 There was a trend for the G₂ of alates from Chinese cabbage to have greater fecundity compared with aphids from cabbage. These differences were significant for the fecundity of the G₂ of alates of both aphid species on Brussels sprout cultivars Fillbasket (30% higher), Red Delicious (35% higher) and Winter Harvest (25% higher) than those reared on cabbage.
• 5 The intrinsic rate of increase for the G₂ of alates of B. brassicae from Chinese cabbage was significantly different on all Brussels sprout cultivars tested. The intrinsic rate of increase differed significantly between aphids reared on either Chinese cabbage or cabbage on cultivars Oliver and Darkmar‐21 (M. persicae) and Red Delicious and Winter Harvest (B. brassicae). The cv. Oliver appeared to be the most consistently good host; Red Delicious was the poorest host overall.

     

Associational resistance or susceptibility: the indirect interaction between chemically‐defended and non‐defended herbivore prey via a shared predator

Many organisms possess chemical defences against their natural enemies, which render them unpalatable or toxic when attacked or consumed. These chemically‐defended organisms commonly occur in communities with non‐ or less‐defended prey, leading to indirect interactions between prey species, mediated by natural enemies. Although the importance of enemy‐mediated indirect interactions have been well documented (e.g. apparent competition), how the presence of prey chemical defences may affect predation of non‐defended prey in terrestrial communities remains unclear. Here, an experimental approach was used to study the predator‐mediated indirect interaction between a chemically‐defended and non‐defended pest aphid species. Using laboratory‐based mesocosms, aphid community composition was manipulated to include chemically‐defended (CD) aphids Brevicoryne brassicae, non‐defended (ND) aphids Myzus persicae or a mixed assemblage of both species, on Brassica oleracea cabbage plants, in the presence or absence of a shared predator (Chrysoperla carnea larvae). Aphid population growth rates, aphid distributions on host plants and predator growth rates were measured. In single‐species treatments, C. carnea reduced M. persicae population growth rate, but had no significant impact on B. brassicae population growth rate, suggesting B. brassicae chemical defences are effective against C. carnea. Chrysoperla carnea had no significant impact on either aphid species population growth rate in mixed‐species treatments. Myzus persicae (ND) therefore experienced reduced predation in the presence of B. brassicae (CD) through a predator‐mediated indirect effect. Moreover, predator growth rates were significantly higher in the M. persicae‐only treatments than in either the B. brassicae‐only or mixed‐species treatments, suggesting predation was impaired in the presence of B. brassicae (CD). A trait‐mediated indirect interaction is proposed, consistent with associational resistance, in which the predator, upon incidental consumption of chemically‐defended aphids is deterred from feeding, releasing non‐defended aphids from predatory control.     

PEMPHIGUS REVISITED: CHANGES IN GEOGRAPHIC VARIATION BUT CONSTANCY IN VARIABILITY AND COVARIATION

Samples of the gall-forming aphids Pemphigus populicaulis and P. populitransversus (both elongate and globular morphs) were re-collected at sites in eastern North America after 13 to 16 years. Twenty-three morphometric characters of the galls, stem mothers, and alate fundatrigeniae were analyzed by univariate and multivariate methods. Varying proportions of the variance of each character are attributable to the four levels of variation—locality, year, year by locality interaction, and among galls (within one year and locality). The year by locality interaction level generally has the greatest variation and is highly significant. Year and locality effects tend to be lower and not significant. The variance components do not exhibit trends with time. Geographic variation patterns of single variables or factor scores in the original and revisited populations show significant spatial structure overall but lack clear-cut spatial patterns, especially clines. Observable patterns of variation match results of the spatial analyses: most characters lack clear trends; patterns in the revisited data do not resemble patterns for the same variables in the original data. Variability profiles for characters change little over the time span and are comparable among and within localities. Covariation among characters over localities is largely maintained during the time interval despite the changes in patterns. Fluctuating interclonal competition among aphids on secondary hosts is believed to cause the marked heterogeneity in space and time among the aphids in the galls.     

Characterization of genetic diversity of nuclear and mitochondrial genomes in Daucus varieties by RAPD and AFLP

The genetic diversity of nuclear genomes of five Daucus species and seven Daucus carota L. subspecies involving 26 accessions was characterized with random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP). AFLP produced more than four times as many discrete bands per reaction compared with RAPD analysis, while both AFLP and RAPD basically led to similar conclusions. The dendrograms constructed with both RAPD and AFLP revealed that all accessions of D. carota were grouped into a major cluster delimited from other Daucus species, in good agreement with the classification by morphological char-acteristics. All accessions of cultivated carrots [(D. carota ssp. sativus (Hoffm.) Arcang.] were clustered in the same group while the variation within D. carota was relatively extensive. Genetic diversity of mitochondrial genomes was also documented with RAPD for the same accessions. The mitochondrial dendrogram differed from that of the nuclear genome, suggesting that nuclear and mitochondrial genomes of some accessions had separate evolutionary histories. Received: 20 September 1997 / Revision received: 19 January 1998 / Accepted: 28 March 1998