Factors driving susceptibility and resistance in aphids that share specialist fungal pathogens (original) (raw)
Related papers
Insects
Pandora neoaphidis and Entomophthora planchoniana (phylum Entomophthoromycota) are important fungal pathogens on cereal aphids, Sitobion avenae and Rhopalosiphum padi. Here, we evaluated and compared for the first time the virulence of these two fungi, both produced in S. avenae cadavers, against the two aphid species subjected to the same exposure. Two laboratory bioassays were carried out using a method imitating entomophthoralean transmission in the field. Healthy colonies of the two aphid species were exposed to the same conidial shower of P. neoaphidis or E. planchoniana, in both cases from a cadaver of S. avenae. The experiments were performed under LD 18:6 h at 21 °C and a successful transmission was monitored for a period of nine days after initial exposure. Susceptibility of both S. avenae and R. padi to fungal infection showed a sigmoid trend. The fitted nonlinear model showed that the conspecific host, S. avenae, was more susceptible to E. planchoniana infection than the ...
European Journal of Entomology, 2007
The performance of the aphid-specific fungal pathogen Pandora neoaphidis was studied in relation to changes in herbivore resources for the pea aphid, Acyrthosiphon pisum, on different host plant species. Dose-response bioassays were conducted with A. pisum which had been reared on dwarf bean then inoculated with P. neoaphidis and returned to dwarf bean or inoculated and transferred to field bean, pea or lucerne. The smallest estimated median lethal concentration (LC50) was 7.7 conidia mm -2 (95% confidence interval 5.4-11.2) for aphids returned to dwarf bean, with LC50s of 13.0 (9.2-19.1) and 14.6 (10.2-21.5) conidia mm -2 for aphids transferred to field bean or pea, respectively. The LC50 when aphids were transferred to lucerne [2941.0 conidia mm -2 (237.3-2.1x10 9 )] was greater than for the other three plants. In a subsequent experiment, A. pisum were reared on pea as well as dwarf bean for four generations before bioassays. The LC50 was 7.3 conidia mm -2 (4.4-12.4) for aphids reared and incubated on dwarf bean, compared to 13.3 (8.0-23.9) and 15.3 (8.8-29.9) conidia mm -2 when aphids were transferred between dwarf bean and pea, and vice versa, respectively. The LC50 for aphids reared then incubated on pea plants was 27.9 (15.8-57.3) conidia mm -2 . Hence, the virulence of P. neoaphidis, measured by LC50, was greatest when A. pisum was reared and maintained on dwarf bean, the plant used for long-term routine culturing of the aphid in our facilities. In conclusion, virulence of P. neoaphidis was greater on plant species to which A. pisum had become adapted during long-term laboratory rearing. Plant resources may affect infection by P. neoaphidis and the fungal entomopathogen will have a greater impact on aphid herbivores which are not suffering physiological stress related to a change in host plant.
Journal of Pest Science, 2019
Symbiosis in insects has been recognized as contributing to their ecological and evolutionary success. In the case of agricultural pests, endosymbionts may help insects colonize and expand their niches, allowing them to use different crops and to confront climatic variation. Moreover, endosymbionts provide improved defences against pathogens, predators, and parasitoids. In aphids, facultative endosymbionts have been found capable of generating these characteristics. However, evidence for this has been gathered from only a few model organisms. Here, we studied the effect of the facultative endosymbiont Regiella insecticola on the predation of Sitobion avenae clones by the ladybird Hippodamia variegata. In the laboratory, we assessed the predation rate of this coccinellid and the concomitant anti-predator behaviour of S. avenae with and without R. insecticola. We also evaluated the effect of the presence of this endosymbiont on the constitutive levels of E-β-farnesene, on the metabolic rate, and on the reproductive performance of S. avenae. All these traits were studied on two common alternative crops: wheat and barley. We found that R. insecticola-infected aphids were more predated irrespective of host plants and did not improve defences against coccinellid predators or metabolic rates on any host plants. Levels of E-β-farnesene were higher on wheat plants, irrespective of the presence of R. insecticola. Interestingly, R. insecticola-infected aphids had increased performance on wheat, while the opposite was true on barley. We discuss our findings based on the importance of secondary symbionts as providers of traits allowing aphids to be very invasive crop pests worldwide.
Endoparasitism in cereal aphids: molecular analysis of a whole parasitoid community
Molecular Ecology, 2008
Insect parasitoids play a major role in terrestrial food webs as they are highly diverse, exploit a wide range of niches and are capable of affecting host population dynamics. Formidable difficulties are encountered when attempting to quantify host-parasitoid and parasitoid-parasitoid trophic links in diverse parasitoid communities. Here we present a DNA-based approach to effectively track trophic interactions within an aphid-parasitoid food web, targeting, for the first time, the whole community of parasitoids and hyperparasitods associated with a single host. Using highly specific and sensitive multiplex and singleplex polymerase chain reaction, endoparasitism in the grain aphid Sitobion avenae (F) by 11 parasitoid species was quantified. Out of 1061 aphids collected during 12 weeks in a wheat field, 18.9% were found to be parasitized. Parasitoids responded to the supply of aphids, with the proportion of aphids parasitized increasing monotonically with date, until the aphid population crashed. In addition to eight species of primary parasitoids, DNA from two hyperparasitoid species was detected within 4.1% of the screened aphids, with significant hyperparasitoid pressure on some parasitoid species. In 68.2% of the hyperparasitized aphids, identification of the primary parasitoid host was also possible, allowing us to track species-specific parasitoid-hyperparasitoid links. Nine combinations of primary parasitoids within a single host were found, but only 1.6% of all screened aphids were multiparasitized. The potential of this approach to parasitoid food web research is discussed.
Aphid-encoded variability in susceptibility to a parasitoid
BMC Evolutionary Biology, 2014
Background: Many animals exhibit variation in resistance to specific natural enemies. Such variation may be encoded in their genomes or derived from infection with protective symbionts. The pea aphid, Acyrthosiphon pisum, for example, exhibits tremendous variation in susceptibility to a common natural enemy, the parasitic wasp Aphidius ervi. Pea aphids are often infected with the heritable bacterial symbiont, Hamiltonella defensa, which confers partial to complete resistance against this parasitoid depending on bacterial strain and associated bacteriophages. That previous studies found that pea aphids without H. defensa (or other symbionts) were generally susceptible to parasitism, together with observations of a limited encapsulation response, suggested that pea aphids largely rely on infection with H. defensa for protection against parasitoids. However, the limited number of uninfected clones previously examined, and our recent report of two symbiont-free resistant clones, led us to explicitly examine aphid-encoded variability in resistance to parasitoids. Results: After rigorous screening for known and unknown symbionts, and microsatellite genotyping to confirm clonal identity, we conducted parasitism assays using fifteen clonal pea aphid lines. We recovered significant variability in aphid-encoded resistance, with variation levels comparable to that contributed by H. defensa. Because resistance can be costly, we also measured aphid longevity and cumulative fecundity of the most and least resistant aphid lines under permissive conditions, but found no trade-offs between higher resistance and these fitness parameters. Conclusions: These results indicate that pea aphid resistance to A. ervi is more complex than previously appreciated, and that aphids employ multiple tactics to aid in their defense. While we did not detect a tradeoff, these may become apparent under stressful conditions or when resistant and susceptible aphids are in direct competition. Understanding sources and amounts of variation in resistance to natural enemies is necessary to understand the ecological and evolutionary dynamics of antagonistic interactions, such as the potential for coevolution, but also for the successful management of pest populations through biological control.
Insect Science
Bacterial endosymbionts have enabled aphids to adapt to a range of stressors, but their effects in many aphid species remain to be established. The bird cherry-oat aphid, Rhopalosiphum padi (Linnaeus), is an important pest of cereals worldwide and has been reported to form symbiotic associations with Serratia symbiotica and Sitobion miscanthi L-type symbiont endobacteria, although the resulting aphid phenotype has not been described. This study presents the first report of R. padi infection with the facultative bacterial endosymbiont Hamiltonella defensa. Individuals of R. padi were sampled from populations in Eastern Scotland, UK, and shown to represent seven R. padi genotypes based on the size of polymorphic microsatellite markers; two of these genotypes harbored H. defensa. In parasitism assays, survival of H. defensa-infected nymphs following attack by the parasitoid wasp Aphidius colemani (Viereck) was 5 fold higher than for uninfected nymphs. Aphid genotype was a major determinant of aphid performance on two Hordeum species, a modern cultivar of barley H. vulgare and a wild relative H. spontaneum, although aphids infected with H. defensa showed 16% lower nymph mass gain on the partially resistant wild relative compared with uninfected individuals. These findings suggest that deploying resistance traits in barley will favor the fittest R. padi genotypes, but symbiontinfected individuals will be favored when parasitoids are abundant, although these aphids will not achieve optimal performance on a poor quality host plant.
Ecological Entomology, 2016
1. The relationship between endosymbionts and insects represent complex eco-evolutionary interactions. Vertically transmitted endosymbionts can be a source of evolutionary novelty by conferring ecologically important traits to their insect hosts, such as protection against natural enemies. Host-endosymbiont associations could constitute an adaptive complex (holobiont) on which selective pressures present in the environment can act, being transferred to the next generation. 2. Although several laboratory-based studies have confirmed host genotype × symbiont interactions, few studies have been directed at those associations in the natural populations and their ability to protect themselves from parasitism pressure at the field level. 3. A field-based approach to study the aphid genotype-endosymbiont associations and its relationship with the total parasitism in the grain aphid Sitobion avenae was conducted. From the field study, experiments were carried out to study the defensive effect of the two most common facultative endosymbionts (Regiella insecticola and Hamiltonella defensa) present in S. avenae against one of the most important parasitoid species, Aphidius ervi. 4. Evidence is presented here of a high specificity of the aphid clone-endosymbiont associations in the field; however, the field and experimental results here do not support a relationship between the aphid clone-endosymbiont associations and a proxy of total parasitism in S. avenae. These findings highlight the importance of particular host clone-endosymbiont couplings as a key factor in gaining an understanding of the coevolutionary dynamics of endosymbionts in nature and their effect on the invasive potential of pest insects.
Microbial Ecology, 2014
Facultative bacterial endosymbionts can play an important role in the evolutionary trajectory of their hosts. Aphids (Hemiptera: Aphididae) are infected with a wide variety of facultative endosymbionts that can confer ecologically relevant traits, which in turn may drive microevolutionary processes in a dynamic selective environment. However, relatively little is known about how symbiont diversity is structured in most aphid species. Here, we investigate facultative symbiont species richness and prevalence among worldwide populations of the cowpea aphid, Aphis craccivora Koch. We surveyed 44 populations of A. craccivora, and detected 11 strains of facultative symbiotic bacteria, representing six genera. There were two significant associations between facultative symbiont and aphid food plant: the symbiont Arsenophonus was found at high prevalence in A. craccivora populations collected from Robinia sp. (locust), whereas the symbiont Hamiltonella was almost exclusively found in A. craccivora populations from Medicago sativa (alfalfa). Aphids collected from these two food plants also had divergent mitochondrial haplotypes, potentially indicating the formation of specialized aphid lineages associated with food plant (host-associated differentiation). The role of facultative symbionts in this process remains to be determined. Overall, observed facultative symbiont prevalence in A. craccivora was lower than that of some other well-studied aphids (e.g., Aphis fabae and Acyrthosiphon pisum), possibly as a consequence of A. craccivora's almost purely parthenogenetic life history. Finally, most (70 %) of the surveyed populations were polymorphic for facultative symbiont infection, indicating that even when symbiont prevalence is relatively low, symbiont-associated phenotypic variation may allow population-level evolutionary responses to local selection.
Multifaceted determinants of host specificity in an aphid parasitoid
Oecologia, 2009
The host specificity of insect parasitoids and herbivores is thought to be shaped by a suite of traits that mediate host acceptance and host suitability. We conducted laboratory experiments to identify mechanisms shaping the host specificity of the aphid parasitoid Binodoxys communis. Twenty species of aphids were exposed to B. communis females in microcosms, and detailed observations and rearing studies of 15 of these species were done to determine whether patterns of host use resulted from variation in factors such as host acceptance or variation in host suitability. Six species of aphids exposed to B. communis showed no signs of parasitism. Four of these species were not recognized as hosts and two effectively defended themselves from attack by B. communis. Other aphid species into which parasitoids laid eggs had low suitability as hosts. Parasitoid mortality occurred in the egg or early larval stages for some of these hosts but for others it occurred in late larval stages. Two hypotheses explaining low suitability were investigated in separate experiments: the presence of endosymbiotic bacteria conferring resistance to parasitoids, and aphids feeding on toxic plants. An association between resistance and endosymbiont infection was found in one species (Aphis craccivora), and evidence for the toxic plant hypothesis was found for the milkweed aphids Aphis asclepiadis and Aphis nerii. This research highlights the multifaceted nature of factors determining host specificity in parasitoids.