Intraspecific Variation In Susceptibility Research Articles

Susceptibility of Eucalyptus trees to defoliation by the Eucalyptus snout beetle, Gonipterus sp. n. 2, is enhanced by high foliar contents of 1,8-cineole, oxalic acidand sucrose and low contents of palmitic and shikimic acid.

Gonipterus sp. n. 2 (Coleoptera, Curculionidae) is an invasive, commercially important weevil that causes large-scale defoliation of Eucalyptus trees. The weevil specifically feeds on young leaves and new shoots, thus reducing tree growth. The weevil displays a very strong preference for certain Eucalyptus genotypes, however, this behaviour and the chemistry underlying it is poorly understood, thereby complicating the selection of resistant trees. To elucidate the feeding preference of Gonipterus sp. n. 2, we assessed the relative levels of susceptibility of 62 Eucalyptus genotypes from 23 species using a laboratory choice assay. This revealed large intraspecific variation in susceptibility to weevil feeding, which for certain species, exceeded the interspecific variation. A semiquantitative metabolite profile analysis on 13 genotypes revealed strong correlations of 10 metabolites to feeding damage. The behavioural effects of the identified compounds were assessed through an in vitro feeding preference assay using artificial diets as well as under field conditions. This revealed three phagostimulants (1,8-cineole, oxalic acidand sucrose) and two feeding deterrent compounds (shikimic acid and palmitic acid) for Gonipterus sp. n. 2. These chemical markers can be applied to tree breeding programmes for the selection of resistant genotypes to reduce damage caused by Gonipterus weevils.

Interspecific and intraspecific variation in susceptibility of two co-occurring pest thrips, Frankliniella occidentalis and Thrips palmi, to nine insecticides.

Field control of pest thrips mainly relies on insecticides, but the toxicity of insecticides can vary among thrips species and populations. In this study, we examined the susceptibility of multiple field populations of two thrips pests, Frankliniella occidentalis, and Thrips palmi, that often co-occur on vegetables, to nine insecticides belonging to seven subgroups. The highest level of variation in susceptibility among F. occidentalis populations was for spinetoram (73.92 fold difference between most resistant and most susceptible population), followed by three neonicotinoids (8.06-15.99 fold), while among T. palmi populations, it was also for spinetoram (257.19 fold), followed by emamectin benzoate, sulfoxaflor, and acetamiprid (23.64-45.50 fold). These findings suggest evolved resistance to these insecticides in some populations of the two thrips. One population of F. occidentalis had a particularly high level of resistance overall, being the most resistant for five of the nine insecticides tested. Likewise, a population of T. palmi had high resistance to all nine insecticides, again suggesting the evolution of resistance to multiple chemicals. For F. occidentalis, the LC95 values of most populations were higher than the field-recommended dosage for all insecticides except chlorfenapyr and emamectin benzoate. For several T. palmi populations, the LC95 values also tended to be higher than recommended dosages, except in the case of emamectin benzoate and spinetoram. Our study found interspecific and intraspecific variations in the susceptibility of two thrips to nine insecticides and multiple resistance in some populations, highlighting the need for ongoing monitoring and resistance management. © 2023 Society of Chemical Industry.

Co‐occurrence of defensive traits in the potato aphid Macrosiphum euphorbiae

1. Insecticide usage selects strongly for resistance in aphid populations, but this could entail fitness costs in other resistance traits. The potato aphid Macrosiphum euphorbiae Thomas exhibits intraspecific variation in susceptibility to parasitism by braconid wasps and provides a suitable species to study the relation between the defensive traits of parasitism and insecticide resistance.2. Clonal lines (23 in total) of M. euphorbiae were established from aphids collected in 2013 from geographically separate populations in the U.K. Clonal lines belonged to five aphid genotypes, but one genotype predominated (78% of samples), and the facultative endosymbiont Hamiltonella defensa was detected in c. 40% of lines.3. Total esterase activity in aphid tissues varied significantly between aphid genotypes and collection areas, but there was no clear pattern in relation to H. defensa infection or between collection sites likely to differ in insecticide pressures.4. Five clonal lines representing low to moderate levels of enzyme activity, which included different aphid genotypes and presence/absence of H. defensa infection, were assayed for their susceptibility to the parasitoid wasp Aphidius ervi Haliday. Aphid mummification varied significantly between aphid genotypes, with low values in one genotype of aphids irrespective of H. defensa presence.5. The results revealed that aphid lines belonging to the parasitism‐resistant genotype exhibited moderate levels of total esterase activity, indicating a competitve advantage for this genotype of M. euphorbiae when exposed to chemical and biological control factors in agroecosystems.

Skin sloughing rate increases with chytrid fungus infection load in a susceptible amphibian

Summary Amphibian chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is responsible for the greatest disease‐driven loss of vertebrate biodiversity in recorded history. Understanding drivers of host susceptibility to this cutaneous disease is hindered by gaps in our knowledge of the host–pathogen relationship. One such overlooked aspect of susceptibility is variation in skin maintenance processes, particularly skin turnover via routine sloughing. It has been suggested that sloughing plays a role in immune defence, by removing skin‐associated microbes. Thus, skin sloughing may play an important role in the pathogenesis of chytridiomycosis. To determine the relationship between skin sloughing and disease progression, we exposed adult Australian green tree frogs (Litoria caerulea) to a local Bd strain and monitored sloughing rates and individual infection loads on a naturalistic cycling temperature regime (15–23 °C). We determined sloughing rates in real‐time by using an array of infrared video cameras to film frog behaviour and monitored infection load before and after sloughing by swabbing and analysis with quantitative PCR. We found that sloughing rate increased with Bd infection load in infected frogs, but sloughing itself did not affect Bd load on the ventral skin surface. Furthermore, Bd infection did not affect the duration of characteristic sloughing behaviour, and sloughing retained rhythmicity even at high infection loads. Although an increased sloughing rate might be considered advantageous for Bd‐infected animals, it does not appear to curb the progression of disease and may actually contribute to the loss of physiological homoeostasis seen in terminally ill frogs by further inhibiting water and electrolyte transport across the skin. By measuring sloughing rates directly for the first time, our results shed light on how Bd interacts with the physiological processes of the skin and indicate that variation in skin sloughing frequency may play a role in the observed inter‐ and intraspecific variation in susceptibility to disease.

Intraspecific variation in susceptibility to dothistroma needle blight within native Scottish Pinus sylvestris

Dothistroma needle blight (DNB), caused by Dothistroma septosporum, is the most important disease currently affecting pine plantations in Britain. Intraspecific variation in susceptibility to DNB has been observed in several pine species, but it is not clear if similar variation occurs in Pinus sylvestris (Scots pine), Britain's only native pine. In three separate experiments 2‐ and 3‐year‐old Scots pine saplings from six native Scottish populations were artificially inoculated with D. septosporum conidial suspensions and incubated under conditions optimal for disease development. Conidial suspensions were produced using a single isolate from northeast Scotland. In one experiment, plants were also treated with various spore suspension concentrations to assess the impact of inoculum load on disease severity. There were no significant interactions between host population, plant height, and experiment/inoculum load (anova, P > 0·05), but population, height and inoculum load all significantly affected disease severity (anova, P < 0·05). Among the 2‐year‐old trees, those from Amat were less susceptible than those from Glen Loyne and Glen Cannich (anova, P < 0·05). Among the 3‐year‐old trees, those from Beinn Eighe were less susceptible than those from Abernethy. Plant height and DNB susceptibility had a slightly negative relationship. The use of a spore suspension with a concentration of 1·6 × 106 spores mL−1 was optimum for disease development. In an in vitro experiment, production of conidia was greater when cultures were incubated in darkness. This paper is the first to report intraspecific variation in DNB susceptibility within Scots pine.

Plant traits predict inter‐ and intraspecific variation in susceptibility to herbivory in a hyperdiverse Neotropical rain forest tree community

Summary A key issue in plant/herbivore interaction research is to understand which plant traits drive differences in herbivore damage. Variation in chemical, physical or phenological traits of plants may all modulate the degree of herbivore damage among species and individuals, yet the relative importance of these factors is still subject to debate, particularly in species‐rich systems such as tropical rain forests. To address this issue, we quantified leaf herbivore damage in 28 common tree species of the Yasuní forest dynamic plot (YFDP) in the Ecuadorian Amazon over 11 months. Census data from the YFDP allowed us to quantify several aspects of tree ecology potentially affecting herbivory including leaf turnover and spatial distribution patterns. We measured six chemical, eight physical and four ecological traits of the focal species. Using a combination of multivariate analyses and phylogenetic generalized linear regression model (PGLS), we assessed trade‐offs between physical and chemical traits and the relative effect of all these traits on leaf herbivore damage. Herbivore damage was highly variable among species and individuals, with leaves on average displaying damage over 13.4% (2.5–29.5%) of their area. We found no significant trade‐off between physical and chemical defences for the 28 studied tree species. Overall, leaf size, shearing resistance, cellulose, ash content and leaf size × ash were the best predictors of herbivore damage. Surprisingly, condensed tannins and latex did not significantly correlate with herbivore damage. In addition, we found no relationships between herbivory and local tree density. However, we did find a weak effect of tree clustering and strong effect of tree leaf turnover rates on herbivore damage. Synthesis. In the western Amazon, leaves are defended against herbivores through a combination of physical (toughness), chemical (toughness‐related elements), and phenological (rapid leaf replacement) characteristics that do not appear to be subject to obvious trade‐offs. Conventional strategies, such as condensed tannins or latex, do not seem to be strongly involved as a defence against herbivores in this community.

Resistance levels of Spanish conifers against Fusarium circinatum and Diplodia pinea

SummaryPitch canker, caused by Fusarium circinatum, and Diplodia shoot blight, caused by Diplodia pinea, are both damaging to pines (Pinus spp.) grown in plantations throughout the world, including Spain. To assess the potential for interspecific differences in susceptibility to contribute to the management of pitch canker and Diplodia shoot blight in the Atlantic region of Spain, the present study was undertaken to characterize the susceptibility of six pine species (P. sylvestris, P. nigra, P. pinaster, P. radiata, P. halepensis and P. pinea) and Douglas‐fir (Pseudotsuga menziesii) to F. circinatum and D. pinea. Based on inoculations of 2‐year‐old trees, Ps. menziesii, P. pinea and P. nigra were the most resistant to F. circinatum, with lesion lengths ranging from 3.7 to 21.5 mm, 2.2 to 12.6 mm and 2.8 to 30.9 mm, respectively. At the other extreme, Pinus radiata was the most susceptible, sustaining lesions that ranged from 8.5 to 74.8 mm in length. Pinus sylvestris, P. pinaster and P. halepensis showed an intermediate response to F. circinatum. Broadly similar results were observed in inoculations with D. pinea, with Ps. menziesii being relatively resistant and P. radiata being highly susceptible. Consistent with these results, field surveys revealed no pitch canker in stands of Ps. menziesii and low severity of Diplodia shoot blight, whereas P. radiata was severely affected by both diseases. Our findings suggest that selection of appropriate species can greatly reduce the risk of damage from two important canker diseases affecting pine plantations in the Atlantic region of Spain. Furthermore, intraspecific variation in susceptibility implies that selection may allow for the enhancement of resistance in otherwise susceptible species.

Phytophthora cinnamomi invasion, a major threatening process to conservation of flora diversity in the South-west Botanical Province of Western Australia

The invasive soilborne plant pathogen Phytophthora cinnamomi Rands is a major threatening process in the South-west Botanical Province of Western Australia, an internationally recognised biodiversity hotspot. Comparatively recent introduction of P. cinnamomi into native plant communities of the South-west Botanical Province of Western Australia since the early 1900s has caused great irreversible damage and altered successional change to a wide range of unique, diverse and mainly susceptible plant communities. The cost of P. cinnamomi infestation to community values is illustrated by examination of direct (mortality curves, changes in vegetation cover) and indirect impacts on biodiversity and ecosystem dynamics, the proportion of Threatened Ecological Communities infested, Declared Rare Flora either directly or indirectly threatened by infestation and estimates of the proportion of the native flora of the South-west Botanical Province susceptible to the pathogen. While direct impacts of P. cinnamomi have been poorly documented in the South-west Botanical Province, even less attention has been given to indirect impact where destruction of the habitat by the pathogen affects taxa not directly affected by infection. Current poor understanding and quantification of indirect impacts of P. cinnamomi through habitat destruction results in an underestimation of the true impact of the pathogen on the flora of the South-west Botanical Province. Considerable variation of susceptibility to P. cinnamomi among and within families of threatened flora and responses of taxa within the genus Lambertia show how classification within family and genus are poor predictors of species susceptibility. Within apparently susceptible plant species, individuals are resistant to P. cinnamomi infection. Intra-specific variation in susceptibility can be utilised in the long-term management of threatened flora populations and needs to be a high research priority. Current control strategies for conservation of flora threatened by P. cinnamomi integrate hygiene and ex situ conservation with disease control using fungicide. Application of the fungicide phosphite has proven effective in slowing progress of P. cinnamomi in infested, threatened communities. However, variation in plant species responses to phosphite application is a major factor influencing effective control of P. cinnamomi in native communities. A greater understanding of the mechanisms of action of phosphite in plant species showing different responses to the fungicide may provide options for prescription modification to increase phosphite effectiveness in a range of plant species. The range of responses to P. cinnamomi infection and phosphite application described for Lambertia taxa suggests that the genus would make an ideal model system to elucidate the mechanisms of resistance to P. cinnamomi and the effectiveness of phosphite against the pathogen.

Variation in multiple traits of vegetative and reproductive seagrass tissues influences plant–herbivore interactions

Plant-herbivore interactions have strong ecological and evolutionary consequences, but have been traditionally overlooked in marine higher plants. Despite recent advances in seagrass ecology that highlight the importance of herbivory, the mechanisms that regulate the feeding behaviour of seagrass consumers remain largely unknown. Herbivores have been shown to reduce the sexual reproductive success of seagrasses through direct consumption of inflorescences and seeds, but we know little about intraspecific variation in susceptibility to grazing of different seagrass tissues. We contrasted the relative palatability of reproductive and vegetative tissues of the temperate seagrass Posidonia oceanica in the field, and we assessed the feeding preferences among these tissues of the main consumers of the plant, the fish Sarpa salpa and the urchin Paracentrotus lividus. Moreover, we identified the plant traits that explained the observed feeding behaviour. We provide strong evidence for herbivore selectivity among seagrass tissues. In the field, 70-90% of inflorescences were damaged by herbivores compared to 3-60% of leaves of similar age. In feeding assays, the urchin P. lividus showed over a twofold preference for reproductive tissue at various stages of development. By contrast, we detected no feeding activity on either leaves or inflorescences from the fish S. salpa, which is known to migrate to deeper waters soon after flowering starts and during the period of fruit maturation. Despite being the preferred food of urchins, inflorescences were chemically defended, had higher levels of phenolics and lower nutrient and calorific content than leaves. We experimentally demonstrated that leaf structural defences are the primary factor in determining urchin feeding preferences. Removal of plant structure results in a drastic shift in urchin selectivity towards the most nutritious and less chemically defended leaf tissue, indicating that multiple mechanisms of defence to herbivory may coexist in seagrasses.

Variation in susceptibility of Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) (Lepidoptera: Noctuidae) in Australia to two Bacillus thuringiensis toxins

Intra-specific variation in susceptibility of Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) in Australia to the Cry1Ac and Cry2Ab δ-endotoxins from Bacillus thuringiensis (Berliner) (Bt) was determined to establish a baseline for monitoring changes that might occur with the use of Bt cotton. Strains of H. armigera and H. punctigera were established from populations collected primarily from commercial farms throughout the Australian cotton belts. Strains were evaluated for susceptibility using two bioassay methods (surface treatment and diet incorporation) by measuring the dose response for mortality (LC 50) and growth inhibition (IC 50). The variation in LC 50 among H. armigera ( n = 17 strains) and H. punctigera ( n = 12 strains) in response to Cry1Ac was 4.6- and 3.2-fold, respectively. The variation in LC 50 among H. armigera ( n = 19 strains) and H. punctigera ( n = 12 strains) to Cry2Ab was 6.6- and 3.5-fold, respectively. The range of Cry1Ac induced growth inhibition from the 3rd to 4th instar in H. armigera ( n = 15 strains) was 3.6-fold and in H. punctigera ( n = 13 strains) was 2.6-fold, while the range of Cry2Ab induced growth inhibition from neonate to 3rd instar in H. armigera ( n = 13 strains) was 4.3-fold and in H. punctigera ( n = 12 strains) was 6.1-fold. Variation in susceptibility was also evaluated for two age classes (neonates and 3rd instars) in laboratory strains of H. armigera and H. punctigera. Neonates of H. punctigera had the same or higher sensitivity to Bt than 3rd instars. Neonates of H. armigera were more sensitive to Cry2Ab than 3rd instars, while being less sensitive to Cry1Ac than 3rd instars. Differences in the two methods of bioassay used affected relative sensitivity of species to Bt toxins, highlighting the need to standardize bioassay protocols.

Budburst Phenology, Plant Vigor, and Host Genotype Effects on the Leaf-Galling Generation ofCallirhytis cornigera(Hymenoptera: Cynipidae) on Pin Oak

Densities of Callirhytis cornigera (Osten Sacken), a cynipid with alternating agamic and sexual generations that develop in woody stem galls and blister-like leaf galls, respectively, often vary among neighboring pin oaks, Quercus palustris Muenchhausen. We studied the ovipositional behavior of agamic wasps and tested several hypotheses to explain intraspecific variation in susceptibility to leaf gall induction. Agamic females laid eggs primarily into green-tip buds. Heavily galled trees had proportionately more vulnerable buds than lightly galled trees during peak oviposition in 1998, supporting the phenological synchrony hypothesis, but not in 1999. Contrary to plant vigor hypothesis predictions, rates of shoot or leaf expansion were similar for lightly and heavily galled trees. Agamic wasps were transferred from heavily infested trees onto shoots of heavily or lightly infested novel trees, or back onto their natal trees, to test for inherent differences in susceptibility to leaf galling. Leaf gall induction was greater on natal than novel trees in 1997, supporting the demic adaptation hypothesis, and there was a trend for greater leaf gall induction on heavily galled than lightly galled novel trees. These patterns, however, did not reoccur in 1998. Although synchrony of emergence with budburst is critical to ovipositional success of agamic C. cornigera, other host-related factors, including those affecting stem gall induction or survival of the agamic generation, probably are more important in determining variation in tree infestation levels. Once a suitable host is colonized, limited wasp dispersal may also contribute to buildup of insular populations on particular trees.

Foliar Concentration of a Single Toxin Creates Habitat Patchiness for a Marsupial Folivore

We examined intraspecific variation in susceptibility to herbivory by common ringtail possums (Pseudocheirus peregrinus) for two species of Eucalyptus, (E. polyanthemos and E. sideroxylon) and the chemical basis for that variation. Using a no-choice protocol, we observed dry matter intakes by common ringtail possums ranging from 3.28 to 44 g·(kg body mass)−0.75·d−1 for E. polyanthemos and from 2.4 to 67 g·(kg body mass)−0.75·d−1 for E. sideroxylon. We investigated, using correlative analyses, the relationships between dry matter intake and a range of foliage chemical characteristics, including measures of nutritional quality (total nitrogen, cellulose, hemi-cellulose, lignin, in vitro dry matter digestibility) and plant secondary chemistry (total phenolics, condensed tannins, cyanogenic glycosides, terpenes, and sideroxylonal, a recently identified Eucalyptus toxin). Significant relationships were identified only for terpenes (and 1,8-cineole in particular) and sideroxylonal. Bioassay experiments confirmed that the foliar concentration of sideroxylonal alone was sufficient to explain the variation observed. To undertake a field study of variation in foliar sideroxylonal and dry matter intake by possums of E. polyanthemos, we developed calibrations of both variables against the near infrared spectra of foliage samples. Acceptable calibration equations were developed, and we applied these to samples collected from a number of E. polyanthemos individuals within an area approximating the home range size of common ringtail possums. We found that foliar sideroxylonal varied from nil to 12.6 mg/g, while predicted dry matter intakes by possums ranged from nil to 42.8 g·(kg body mass)−0.75·d−1. We conclude that significant patchiness in nutritional quality of foliage, resulting from variation in foliar concentrations of a single compound, exists at a scale relevant to the feeding decisions of individual animals.

FOLIAR CONCENTRATION OF A SINGLE TOXIN CREATES HABITAT PATCHINESS FOR A MARSUPIAL FOLIVORE

We examined intraspecific variation in susceptibility to herbivory by common ringtail possums (Pseudocheirus peregrinus) for two species of Eucalyptus, E. polyanthemos and E. sideroxylon, and the chemical basis for that variation. Using a no-choice protocol, we observed dry matter intakes by common ringtail possums ranging from 3.28 to 44 g.kg body mass-0.75.d-1 for E. polyanthemos and 2.4 to 67 g.kg body mass-0.75.d-1 for E. sideroxylon. We investigated, using correlative analyses, the relationships between dry matter intake and a range of foliage chemical characteristics, including measures of nutritional quality (total nitrogen, cellulose, hemi-cellulose, lignin, in vitro dry matter digestibility) and plant secondary chemistry (total phenolics, condensed tannins, cyanogenic glycosides, terpenes and sideroxylonal, a recently identified Eucalyptus toxin). Significant relationships were identified only for terpenes (and 1,8-cineole in particular) and sideroxylonal. Bioassay experiments confirmed that the foliar concentration of sideroxylonal alone was sufficient to explain the variation observed. To enable a field study of variation in foliar sideroxylonal and dry matter intake by possums of E. polyanthemos, we developed calibrations of both variables against the Near Infrared spectra of foliage samples. Acceptable calibration equations were developed and we applied these to samples collected from a number of E. polyanthemos individuals within an area approximating the home range size of common ringtail possums. We found that foliar sideroxylonal varied from nil to 12.6 mg/g, and predicted dry matter intakes by possums ranged from nil to 42.8 g.kg body mass-0.75.d-1. We conclude that significant patchiness in nutritional quality of foliage, resulting from variation in foliar concentrations of a single compound, exists at a scale relevant to the feeding decisions of individual animals.