Aphid Aphis Nerii Research Articles

Exploring horizontal transfer of mariner transposable elements among ants and aphids

Aphids and ants are mutualistic species with a close space-time relationship, which may facilitate the occurrence of horizontal transfer events between these insect groups. Myrmar-like mariner elements were previously isolated from two ant (Myrmica ruginodis and Tapinoma ibericum) and two aphid species (Aphis fabae and Aphis hederae). The aim of this work is to determine the presence of Myrmar-like mariner elements in new ant and aphid species, as well as to analyze the likelihood of horizontal transfer events between these taxa. To accomplish this, the Myrmar-like element has been isolated from five aphid species and six ant species. Among these new analyzed species, full-length Myrmar-like mariner elements with very high sequence similarity have been isolated from the aphids Aphis nerii, Aphis spiraecola, Brachycaudus cardui, and Rhopalosiphum maidis as well as from the ants Lasius grandis and Lasius niger, even though aphids and ants belong to two insect orders (Hemiptera and Hymenoptera) that have evolved independently for at least 300 million-years. Both Lasius species establish frequent mutualistic relationships with multiple aphid species, including A. nerii, A. spiraecola, and B. cardui. The study of the putative protein encoded by them and the phylogenetic analysis suggests that they could be active transposons shared by aphids and ants through horizontal transfer events. Additionally, mariner elements with internal deletion were found in several aphids and one ant species, showing a high degree of sequence similarity among them. The characteristics of these elements with internal deletion suggest a complex origin involving various evolutionary processes, possibly including also horizontal transfer events. Myrmar-like elements have also been isolated from the other ant species, although without similarity with the aphid mariner sequences. Myrmar-like elements are also present in phylogenetically distant insect species, as well as in one crustacean species. The phylogenetic study carried out with all Myrmar-like elements suggests the probable occurrence of horizontal transfer events.

Contribution of Surrounding Flowering Plants to Reduce Abundance of Aphis nerii (Hemiptera: Aphididae) on Oleanders (Nerium oleander L.)

Oleander is very frequently planted as an ornamental shrub in urban areas of the Mediterranean. Its most common pest is the aphid Aphis nerii, and heavy infestations produce aesthetic damage and disturbances to the citizens, and they are frequently sprayed with insecticides in order to reduce the population density. One alternative method is conservation biological control which is enhanced by the provisioning of alternative food, refuges, and reproduction sites. In this study, the usefulness of four flowering service plants (Lobularia maritima, Calendula officinalis, Coreopsis grandiflora, and Achillea millefolium) is evaluated for aphid infestation levels and aphid natural enemy abundances. Aphid levels were consistently lower in oleander plots surrounded by service plants. Natural enemy abundances tended to be higher in plots surrounded by service plants, but significant differences could not be found until the fourth year of the study, when more lacewings, total predators, and mummies were higher in plots surrounded by service plants. On these plots, hoverflies, ladybeetles, and lacewings were the most common predators. Paragus sp. and Hippodamia variegata were the prevalent hoverfly and ladybeetle species, respectively. The potential toxicity effect on the prevalence of natural enemy species is discussed. On service plants, significantly more hoverflies were recorded on L. maritima than on C. officinalis and C. grandiflora, and more true bugs were recorded on C. officinalis and A. millefolium than on L. maritima or C. grandiflora. Our results suggest that planting service plants (such as sweet alyssum, marigold, or yarrow) surrounding oleanders can improve conservation biological control by enhancing the abundance of aphid natural enemies and thus a reduction of the abundance of A. nerii.

Arbuscular mycorrhizal fungi mediate herbivore‐induction of plant defenses differently above and belowground

Plants are exposed to herbivores and symbionts above and below ground. Herbivores above ground alter plant defenses in both leaves and roots, affecting plant–herbivore interactions above and below ground. Root symbionts, such as arbuscular mycorrhizal fungi (AMF), also influence the defenses of leaves and roots, and alter plant responses to herbivory. However, we lack an understanding of how AMF mediate plant responses to herbivores simultaneously in above and belowground plant tissues, despite the ubiquity of such interactions and their consequences for ecological communities. In a full factorial experiment, we subjected plants of four milkweed (Asclepias) species under three levels of AMF inoculum availability to damage by aphids Aphis nerii, caterpillars Danaus plexippus, or no herbivores. We then measured foliar and root cardenolides (chemical defenses), leaf toughness, latex exudation (physical defenses), foliar carbon, nitrogen, and phosphorous concentrations, plant biomass, and levels of AMF colonization of roots.Plants inoculated with AMF generally produced tougher leaves with higher cardenolide concentrations than did plants without AMF. In contrast, root cardenolides were altered by AMF inoculum availability in a plant species‐specific manner. The relative induction or suppression of foliar cardenolides and leaf toughness by herbivores was altered strongly by the level of AMF inoculum available to plants. However, AMF did not influence caterpillar‐induction or aphid‐suppression of root cardenolides. In addition, herbivore feeding induced substantial changes in levels of AMF colonization of roots in a plant species‐specific manner. We demonstrate that the availability of AMF in soil alters herbivore induction and suppression of plant defenses strongly, and does so differently in above and belowground plant tissues. Furthermore, we show that herbivore feeding alters levels of AMF colonization substantially, completing a feedback loop between above‐ and belowground organisms. Our study suggests that indirect interactions between AMF and herbivores may have community‐wide consequences by altering plant phenotype above and below ground.

What doesn’t kill you makes you stronger: The burdens and benefits of toxin sequestration in a milkweed aphid

Abstract Specialized insect herbivores commonly co‐opt plant defences for protection against predators, but the costs, benefits and mechanisms of sequestration are poorly understood. We quantified sequestration of toxic cardenolides by the specialist aphid Aphis nerii when reared on four closely related milkweed (Asclepias) species with >20‐fold variation in cardenolide content, and in the presence or absence of generalist ladybug predators. Increasing concentrations of apolar plant cardenolides increased sequestered amounts in aphids. High concentrations in plants impaired aphid population growth, but also reduced the top‐down effects of predators. An in vitro enzymatic assay of total cardenolides in aphid bodies using the cardenolides’ target (animal Na+/K+‐ATPase) revealed that the subset of sequestered cardenolides is disproportionally more toxic than cardenolides in leaves. All aphids accumulated two cardenolides not present in their host plant, even on plants with very low foliar cardenolide concentrations. Sequestration of potent cardenolides by A. nerii thus involves passive, concentration‐dependent uptake from the host plant, as well as a presumably more active mechanism of modification and up‐concentration of plant cardenolides. The concentration of toxins in the host plant thus not only determines the negative impacts on growth and performance of an aphid, but also the ease and efficiency by which toxins are sequestered for the aphid’s defence, making the costs and benefits of plant toxins highly context‐dependent for both the plant and the herbivore. Therefore, variation in plant toxins is of central importance for co‐evolutionary plant–insect interactions, particularly in environments with variable predator pressure. A plain language summary is available for this article.

Reciprocal interactions between native and introduced populations of common milkweed, Asclepias syriaca, and the specialist aphid, Aphis nerii

Following its introduction into Europe (EU), the common milkweed (Asclepias syriaca) has been free of most specialist herbivores that are present in its native North American (NA) range, except for the oleander aphid Aphis nerii. We compared EU and NA populations of A. nerii on EU and NA milkweed populations to test the hypothesis that plant–insect interactions differ on the two continents. First, we tested if herbivore performance is higher on EU plants than on NA plants, because the former have escaped most of their herbivores and have perhaps been selected for lower defence levels following introduction. Second, we compared two A. nerii lines (one from each continent) to test whether genotypic differences in the herbivore may influence species interactions in plant–herbivore communities in the context of species introductions. The NA population of A. nerii developed faster, had higher fecundity and attained higher population growth rates than the EU population. There was no overall significant continental difference in aphid resistance between the plants. However, milkweed plants from EU supported higher population growth rates and faster development of the NA line of A. nerii than plants from NA. In contrast, EU aphids showed similar (low) performance across plant populations from both continents. In a second experiment, we examined how chewing herbivores indirectly mediate interactions between milkweeds and aphids, and induced A. syriaca plants from each continent by monarch caterpillars (Danaus plexippus) to compare the resulting changes in plant quality on EU aphid performance. As specialist chewing herbivores of A. syriaca are only present in NA, we expected that plants from the two continents may affect aphid growth in different ways when they are challenged by a specialist chewing herbivore. Caterpillar induction decreased aphid developmental times on NA plants, but not on EU plants, whereas fecundity and population growth rates were unaffected by induction on both plant populations. The results show that genetic variation in the plants as well as in the herbivores can determine the outcome of plant–herbivore interactions.

Asymmetry of plant‐mediated interactions between specialist aphids and caterpillars on two milkweeds

Summary Plant‐mediated interactions between co‐occurring herbivores play an important role in insect herbivore communities. Although induced resistance pathways associated with jasmonic acid and salicylic acid are often implicated in such plant‐mediated interactions, there are few examples from non‐model systems involving specialized herbivores that regularly interact in nature. Here, we tested reciprocal impacts between co‐occurring specialist herbivores from two feeding guilds, monarch caterpillars Danaus plexippus and oleander aphids Aphis nerii, on two co‐occurring and closely related, but defensively contrasting milkweeds, Asclepias syriaca and A. tuberosa. Larvae grew 38% faster on aphid‐infested A. syriaca compared to controls. Reciprocally, aphid growth was >50% lower on caterpillar‐damaged A. syriaca compared to controls. While caterpillar feeding on A. syriaca induced a jasmonate burst and higher defensive end products (cardenolides and latex), this induction was substantially attenuated in the presence of aphids. We found a negative correlation between jasmonic acid and salicylic acid only on A. syriaca infested by both caterpillars an aphids. Asclepias tuberosa displayed distinct hormonal dynamics and lacked induction of defensive end products. Accordingly, we found no evidence for plant‐mediated interactions between monarchs and aphids on A. tuberosa. Thus, A. syriaca has specific responses to each herbivore, but if challenged simultaneously, the outcome is asymmetric: monarchs benefit from defence attenuation by aphids, while aphids are impaired by monarch feeding. Our results suggest phytohormonal trade‐offs induced by two feeding guilds can differ between closely related plant species, and our notion of trade‐offs in defence based on phytohormonal pathways would improve with further comparative designs from both model and non‐model systems.

Insecticidal activity of chitosans of different molecular weights and chitosan-metal complexes against cotton leafworm Spodoptera littoralis and oleander aphid Aphis nerii

As an alternative to synthetic pesticides, chitosan has received much attention as a biopolymer active against some agricultural pests. The, insecticidal activity of chitosans of four molecular weights (2.27 × 10<sup>5</sup>,3.60 × 10<sup>5</sup>,5.97 × 10<sup>5</sup>,and9.47 × 10<sup>5 </sup>g/mol) was investigated against two species of arthropod pests: oleander aphid Aphis nerii and cotton leafworm Spodoptera littoralis. In addition, the most active chitosan of 2.27 × 10<sup>5 </sup>g/mol was chemically modified with metals of Ag(I), Cu(II), Ni(II), and Hg(II) to give corresponding chitosan-metal complexes. Larval mortality, growth inhibition, and antifeedant activities for third instar larvae of S. littoralis were evaluated at 4 g (a.i.) chitosan/kg diet. Chitosan of 2.27 × 10<sup>5 </sup>g/mol and its complexes with Ni and Hg were the most active compounds. The results against A. nerii indicated that chitosans of 3.60 × 10<sup>5</sup> and 5.97 × 10<sup>5 </sup>g/mol showed high activity among the different molecular weights in leaf-dip bioassay after 24 h of treatment with 48 and 49% mortalities, respectively, at 1000 mg/l. All compounds had a systemic effect against A. nerii. Chitosans of 2.27 × 10<sup>5</sup>,3.60 × 10<sup>5</sup>,and5.97 × 10<sup>5 </sup>g/mol showed the highest efficacy at all concentrations tested; however, chitosan-Cu was significantly the most active among the complexes.

Insects Associated with MilkweedCalotropis procera(Ait.) Ait. in the Ibex Reserve in the Central Region of the Kingdom of Saudi Arabia

The insect fauna of the native milkweed plant Calotropis procera (Ait.) Ait. in the Ibex Reserve, in the Central Region of the Kingdom of Saudi Arabia was studied. Insects were sampled bimonthly from May 2007 to late April 2008, and then irregularly until June 2011. Ninety-nine insect species belonging to eight orders, 43 families and 80 genera were found to have some type of association with the plant during the period of sampling. The carpenter moth, Semitocossus Johannes (Staudinger), scale insect Contigaspis zilla (Hall) and milkweed aphid Aphis nerii (Boyer de Fonscolombe) were pests attacking the plant. Nine taxa collected represent new country records for Saudi Arabia: Clambus sp. (Coleoptera, Clambidae); Angiometopa sp. (Diptera, Sarcophagidae); Steleoneura sp. (Diptera: Tachinidae); Goniurellia longicauda Freidberg (Diptera, Tephritidae); P silochalcis sp. (Hymenoptera, Chalcididae); Odynerus blanchardianus Saussure (Hymenoptera, Chrysididae); Nomioides kenyensis Pesenko & Pauly (Hymenoptera, Halictidae); Cremastus aegyptiacus Szepligeti (Hymenoptera, Ichneumonidae) and Cerceris chlorotica Spinola (Hymenoptera, Sphecidae).

Composition and Epigenetic Markers of Heterochromatin in the Aphid Aphis nerii (Hemiptera: Aphididae)

A detailed karyotype analysis of the oleander aphid Aphis nerii focusing on the distribution, molecular composition and epigenetic modifications of heterochromatin was done in order to better understand the structure and evolution of holocentric/holokinetic chromosomes in aphids. The female karyotype (2n = 8) consisted of 3 pairs of autosomes and a pair of X chromosomes that were the longest elements in the karyotype and carried a single, terminally located nucleolar organizer region. Males showed 2n = 7 chromosomes due to the presence of a single X chromosome. Heterochromatin was located in the X chromosomes only and consisted of 4 satellite DNAs that have been identified. A. nerii constitutive heterochromatin was enriched in mono-, di- and tri-methylated H3 histones and HP1 proteins but, interestingly, it lacked DNA methylation that was widespread in euchromatic chromosomal regions. These results suggest that aphid heterochromatin is assembled and condensed without any involvement of DNA methylation.

COEXISTENCE OF THREE SPECIALIST APHIDS ON COMMON MILKWEED,ASCLEPIAS SYRIACA

Coexistence of host-specific herbivores on plants is believed to be governed by interspecific interactions, but few empirical studies have systematically unraveled these dynamics. We investigated the role of several factors in promoting coexistence among the aphids Aphis nerii, Aphis asclepiadis, and Myzocallis asclepiadis that all specialize on common milkweed (Asclepias syriaca). Competitive exclusion is thought to occur when interspecific competition is stronger than intraspecific competition. Consequently, we investigated whether predators, mutualists, or resource quality affected the strength of intra- vs. interspecific competition among aphids in factorial manipulations of competition with exposure to predation, ants, and variable plant genotypes in three separate experiments. In the predation x competition experiment, predators reduced aphid per capita growth by 66%, but the strength of intra- and interspecific competition did not depend on predators. In the ants x competition experiment, ants reduced per capita growth of A. nerii and M. asclepiadis (neither of which were mutualists with ants) by approximately one-half. In so doing, ants ameliorated the negative effects of these competitors on ant-tended A. asclepiadis by two-thirds, representing a novel benefit of ant-aphid mutualism. Nevertheless, ants alone did not explain the persistence of competitively inferior A. asclepiadis as, even in the presence of ants, interspecific competition remained stronger than intraspecific competition. In the plant genotype x competition experiment, both A. asclepiadis and M. asclepiadis were competitively inferior to A. nerii, with the strength of interspecific competition exceeding that of intraspecific competition by 83% and 23%, respectively. Yet these effects differed among milkweed genotypes, and there were one or more plant genotypes for each aphid species where coexistence was predicted. A synthesis of our results shows that predators play little or no role in preferentially suppressing competitively dominant A. nerii. Nonetheless, A. asclepiadis benefits from ants, and A. asclepiadis and M. asclepiadis may escape competitive exclusion by A. nerii on select milkweed genotypes. Taken as a whole, the coexistence of three host-specific aphid species sharing the same resource was promoted by the dual action of ants as antagonists and mutualists and by genetic diversity in the plant population itself.

Coexisting congeners: demography, competition, and interactions with cardenolides for two milkweed‐feeding aphids

Explaining the coexistence of closely related species sharing a single resource has been a long‐standing challenge in ecology. Here we report on studies comparing the aphids Aphis nerii and A. asclepiadis that feed sympatrically on the milkweed Asclepias syriaca in northeastern North America. We sought to identify tradeoffs among species’ attributes that might promote coexistence, but in most instances A. nerii was superior to A. asclepiadis. Aphis nerii was 84% more fecund, fed upon 880% more phloem sap, and was affected 70% less by intraspecific competition as compared to A. asclepiadis. In interspecific competition, A. nerii reduced A. asclepiadis abundance by 77%, whereas A. asclepiadis did not affect A. nerii. In dispersal trials, 10% of winged A. nerii but only 1% of A. asclepiadis successfully moved from non‐host plants to A. syriaca. We also investigated whether there were differences in aphid interactions with milkweed cardenolides. Jasmonic acid increased milkweed cardenolides by 33%, a realistic amount similar to that induced by several leaf‐chewing herbivores. Nevertheless, jasmonate‐induced cardenolides failed to affect aphid performance and aphid feeding had no effect on milkweed cardenolide concentration. Yet cardenolides were important for aphid resistance to predators; A. nerii sequestered 25% more cardenolides and was preyed upon 50% less than A. asclepiadis. Interactions with cardenolides thus again favored A. nerii over A. asclepiadis. Given that A. nerii and A. asclepiadis are decidedly not equivalent in their demography, competitive ability, defense and dispersal, our results strongly refute the notion that neutral processes can explain coexistence of these aphids. Based on field observations, we propose two tradeoffs – timing of milkweed colonization and relationships with ants – as putative mechanisms for the coexistence of these congeners.

Effects of variation among plant species on the interaction between a herbivore and its parasitoid

Abstract. 1. Previous studies have demonstrated that phenotypic traits of plants have the potential to affect interactions between herbivores and their natural enemies. Consequently, the impact of natural enemies on herbivore vital rates and population dynamics may vary among plant species. This study was designed to investigate the potential for density‐dependent parasitism of an aphid herbivore feeding on six different host plant species.2. Population densities of the aphid Aphis nerii B de F (Homoptera: Aphididae) and its parasitoid Lysiphlebus testaceipes Cresson (Hymenoptera: Braconidae) were recorded within a single growing season on six different species of milkweed in the genus Asclepias L. (Asclepiadaceae). Asclepias species are known to vary in their quality as food for herbivores. Although data on plant quality were not available in this study, population data were analysed to determine the effects of different Asclepias species on rates of parasitism and aphid population growth.3. Parasitism rates of A. nerii varied among Asclepias species but were temporally density dependent over at least some range of aphid density on all plant species. Aphid population growth rates also varied among Asclepias species, and declined with an increase in the maximum parasitism rates among plant species; however, in no case was density‐dependent parasitism sufficient to prevent exponential population growth of aphids within the growing season. The results serve to emphasise that, if natural enemies are to regulate herbivore populations, density‐dependent mortality is a necessary, but not sufficient, condition for regulation.

Growth, development, and survival of a generalist predator fed single- and mixed-species diets of different quality.

It is often assumed that prey species consumed by generalist predators are largely, though not entirely, equivalent in terms of their value to the predators. In contrast to this expectation, laboratory feeding experiments uncovered distinctly varied developmental responses of a generalist predator, the wolf spider Schizocosa, to different experimental diets. Naive Schizocosa attacked and fed upon all the prey species offered; however, highly divergent patterns of survival, development, and growth of Schizocosa spiderlings reared on different single-prey diets revealed a wide spectrum of prey qualities. Spiderlings fed the collembolan Tomocerus bidentatus sustained the highest overall rates of survival, growth, and development. Fruit flies (Drosophila melanogaster) were intermediate-quality prey: spiders fed Drosophila initially exhibited rates of survival, growth, and development equal to those of spiders on a diet of T. bidentatus, but after about 3 months, rates declined markedly. Fungus gnats (Sciaridae; Bradysia sp.) and conspecfic spiderlings are low-quality prey for Schizocosa: a sole diet of either of these prey types resulted in positive but markedly submaximal rates of growth, retarded rates of development, and survival rates much lower than that supported by a diet of Drosophila. Worst were the collembolans Folsomia candida and Isotoma trispinata, and the aphid Aphis nerii: spiderlings fed solely one of these species did not grow and died without molting. A. nerii is classified as poor quality because survival was no better than that of starved controls. F. candida and I. trispinata were toxic: survival of Schizocosa hatchlings fed these collembolans was lower than that of starved controls. A mixed diet of T. bidentatus and fruit flies yielded positive synergistic effects with respect to growth, but development and rate of survival were similar to those of spiders on a sole diet of T. bidentatus. Including toxic prey did not produce a better diet, while inclusion of toxic prey with prey of higher quality created diets that were no better than the toxic prey alone. The results of these experiments suggest that prey species that are similar in morphology and behavior, and that are initially killed and consumed, may differ dramatically in their suitability as food for generalist arthropod predators.

An investigation of preferential feeding habit in fourAsclepiadaceae by the Aphid,Aphis nerii B. de F.

Penetration of the stems ofAraujia sericofera, Asclepias curassavica, Cynanchum ellipticum andSarcostemma viminale by stylets of the aphidAphis nerii was studied with light and differential interference contrast microscopes. Of a total of 118 stylets and 446 stylet tracks observed in cross-sections of stems of the fourAsclepiadaceae, 97 stylets and 372 stylet tracks terminated within the internal primary phloem. Of the remainder, 15 stylets and 74 tracks terminated within the external primary phloem. 22 stylets and 179 of the stylet tracks penetrated the external phloem on the way to the internal phloem. Of these, only four stylets and 32 of the stylet tracks showed signs of attempted probes of the external phloem. It is suggested thatAphis nerii may obtain not only its essential food requirements but also cardiac glycosides as a basis for chemical aposematism.

Cardiac glycosides in the oleander aphid, Aphis nerii

Cardiac glycosides were found in the aposematic aphid Aphis nerii fed on both Nerium oleander and Asclepias curassavica. The absence of oleandrin and calactin in the body tissues of this insect suggests they are absent from the phloem on which the aphids are believed to feed.