Fatty alcohols, a minor component of the tree tobacco surface wax, are associated with defence against caterpillar herbivory.

Despite decades of research resulting in a comprehensive understanding of epicuticular wax metabolism, the function of these almost ubiquitous metabolites in plant-herbivore interactions remains unresolved. In this study, we examined the effects of CRISPR-induced knockout mutations in four Nicotiana glauca (tree tobacco) wax metabolism genes. These mutations cause a wide range of changes in epicuticular wax composition, leading to altered interactions with insects and snails. Three interaction classes were examined: chewing herbivory by seven caterpillars and one snail species, phloem feeding by Myzus persicae (green peach aphid) and oviposition by Bemisia tabaci (whitefly). Although total wax load and alkane abundance did not affect caterpillar growth, a correlation across species, showed that fatty alcohols, a minor component of N. glauca surface waxes, negatively affected the growth of both a generalist caterpillar (Spodoptera littoralis) and a tobacco-feeding specialist (Manduca sexta). This negative correlation was overshadowed by the stronger effect of anabasine, a nicotine isomer, and was apparent when fatty alcohols were added to an artificial lepidopteran diet. By contrast, snails fed more on waxy leaves. Aphid reproduction and feeding activity were unaffected by wax composition but were potentially affected by altered cutin composition. Wax crystal morphology could explain the preference of B. tabaci to lay eggs on waxy wild-type plants relative to both alkane and fatty alcohol-deficient mutants. Together, our results suggest that the varied responses among herbivore classes and species are likely to be a consequence of the co-evolution that shaped the specific effects of different surface wax components in plant-herbivore interactions.

A mutation increases the specificity to plant compounds in an insect chemosensory protein.

Host plant recognition are highly dependent on chemosensory perception, which involves chemosensory proteins (CSPs) that bind key chemical compounds the host plants. In this work, we hypothesize that two closely related aphid taxa, which differ in diet breadth, also differ in their CSPs. We detected a non-synonymous difference (lysine for asparagine) between M. persicae sensu stricto (Mpp) and the subspecies M. p. nicotianae (Mpn) in the sequence of a CSP (CSP5). We modeled in silico the binding capacity of both CSP5s variants with 163 different potential ligands from their host plants (120 unique from tobacco, 29 unique from peach, and 14 common ligands). After docking analysis with all ligands, we selected the three best ligands for each variant to perform molecular dynamics (tobacco: 2-cyclopentene-1,4-dione, salicylaldehyde, and benzoic acid; peach: phenol, valeric acid, and benzonitrile). The binding energy of the MpnCSP5 model to the studied ligands was, in all cases, lower than with the MppCSP5 model. The ligands from the host plants showed more stable binding with MpnCSP5 than with MppCSP5. This result suggests that the set of CSPs studied among M. persicae s. str. and M. p. nicotianae are very similar, but focusing on the CSP5 protein, we found a single key mutation that increases affinities for host compounds for M. p. nicotianae, which might have contributed to the specialization to tobacco. This study provides new insights into an evolutionary trend toward specificity in a binding protein.

Differential expression of candidate defense genes of poplars in response to aphid feeding.

Species belonging to the genus Populus (poplars) produce a series of defensive proteins in response to insect damage. Proteinase inhibitors, polyphenol oxidases, and chitinases are the most relevant and intensively studied proteins. Most of the knowledge about the relation between these proteins and herbivores has been obtained from studies with chewing insects. Nothing is known about whether phloem-feeder insects such as aphids are able to trigger a comparable response. In the current study, the expression of genes encoding a Kunitz trypsin inhibitor 3 (KTI3), a polyphenol oxidase 1 (PPO1), and a class I chitinase (CHI) was characterized in two poplar hybrids (one resistant hybrid and one susceptible hybrid, to aphids) attacked by the aphid Chaitophorus leucomelas Koch. The expression pattern was analyzed using a semiquantitative reverse transcription-polymerase chain reaction approach. The expression of KTI3 was increased by aphids only in the aphid-susceptible hybrid. Differently, PPO1 expression was increased by aphids in the aphid-resistant hybrid. The expression of CHI was down-regulated by aphids in the susceptible hybrid. This is the first study to report the differential expression of poplar defense genes in response to phloem-feeder insects such as aphids. The findings from the current study suggest that the expression levels of defensive proteins are affected by poplar genotype and by aphid infestation.

Phylogeographical analysis of neotropical Rhagoletis (Diptera: Tephritidae): did the Andes uplift contribute to current morphological differences? / Análisis filogeográfico de Rhagoletis neotropicales (Diptera: Tephritidae): ¿ha contribuido el levantamiento de los Andes a explicar las actuales diferencias morfológicas?

Neotropical Rhagoletis species are arranged in four groups: nova,psalida,striatella and ferruginea, which include 18 species. On both sides of the Andes, the evolution of morphological differences among these groups has been suggested to be related to the Andes uplift process. In order to test this hypothesis, a phylogenetic analysis of morphological and molecular data was performed. The results suggest that: 1) Neotropical species of Rhagoletis constitute a separate group from Paleartic and North American species, with the only exception being a member of the striatella group having a certain association with the northern species. 2) Neotropical species seem to form a monophyletic clade, although statistical support for this is weak. 3) The split of South American Rhagoletis from other groups was dated at 4.333 million years ago, which is before the emergence of a continuous landbridge between Central and South América. 4) Within species distributed in South América, morphological and molecular data were coincident, placing species of the ferruginea group separate from the other Neotropical Rhagoletis. 5) The divergence of the ferruginea group from the other groups was dated at 3.882 million years ago, which is before the last uplift of the Andes. These results suggest that diversification of the ferruginea,psalida and nova groups, on each side of the Andes, was the result of a vicariant separation followed by dispersal and isolation processes. Thus, these results support the hypothesis that the Andes uplift has played an important role in Neotropical Rhagoletis diversification.

Las especies de Rhagoletis neotropicales han sido agrupadas en cuatro grupos: nova,psalida,striatella y ferruginea, constituyendo 18 especies. Se han descrito diferencias morfológicas entre estas especies a ambos lados de la cordillera de los Andes que podrían relacionarse con el proceso de levantamiento cordillerano. En este trabajo se evalúa esta hipótesis usando análisis filogenético de atributos morfológicos y moleculares. Los resultados muestran que: a) las especies Neotropicales de Rhagoletis constituyen un grupo separado de las especies Palearticas y Norteamericanas, con la excepción de un miembro del grupo striatella el cual presenta cierta asociación con las especies Norteamericanas; 2) Las especies Neotropicales parece conformar un clado monofilético; 3) La separación de los grupos Sudamericanos de otros grupos fue estimada en 4.333 millones de años antes del presente, proceso anterior a la emergencia del puente de tierra entre América Central y Sudamérica; 4) Dentro de las especies con distribución Sudamericana, los caracteres morfológicos y moleculares coinciden en ubicar algunas especies del grupo ferruginea separadas de especies de Rhagoletis Neotropicales. 5) La separación del grupo ferruginea fue estimada en 3.882 millones de años antes del presente, evento que precede al último levantamiento de los Andes. La diversificación de los grupos ferruginea,psalida y nova a uno y otro lado de la cordillera de los Andes parece responder inicialmente a un proceso vicariante y posteriores eventos de dispersión y aislamiento. Estos resultados sugieren que el levantamiento de los Andes habría participado en los patrones de diversificación de las Rhagoletis Neotropicales.