Electroantennographic Responses of Cerambyx welensii Küster to Host-Related Volatiles

Wood-boring insects, such as Cerambyx welensii Küster, are involved in oak decline in Mediterranean areas. To advance our understanding of the olfactory perception of C. welensii, we recorded electroantennographic (EAG) responses from male and female antennae to 32 tree volatile organic compounds typical of emissions from its main Quercus L. hosts, and also analysed the dose-dependent response. Cerambyx welensii antennae responded to 24 chemicals. Eight odorants elicited the highest EAG responses (normalized values of over 98%): 1,8-cineole, limonene-type blend, β-pinene, pinene-type blend, sabinene, α-pinene, turpentine and (E)-2-hexenal. Cerambyx welensii exhibits a broad sensitivity to common tree volatiles. The high EAG responses to both limonene- and pinene-type blends suggest the detection of specific blends of the main foliar monoterpenes emitted by Q. suber L. and Q. ilex L. (limonene, α- and β-pinene, sabinene and myrcene), which could influence the intraspecific host choice by C. welensii, and in particular, females may be able to detect oak trees with a limonene-type chemotype. In addition, C. welensii showed high antennal activity to some odorants that characterize emissions from non-host tree species (1,8-cineole, β-pinene, α-pinene, turpentine, δ3-carene and camphene). The results obtained may be applicable to optimize monitoring and mass-trapping programmes in an integrated pest management context.

Characterization of Actinomycetes Strains Isolated from the Intestinal Tract and Feces of the Larvae of the Longhorn Beetle Cerambyx welensii

Actinomycetes constitute a large group of Gram-positive bacteria present in different habitats. One of these habitats involves the association of these bacteria with insects. In this work, we have studied twenty-four actinomycetes strains isolated from the intestinal tract and feces from larvae of the xylophagous coleopteran Cerambyx welensii and have shown that seventeen strains present hydrolytic activity of some of the following substrates: cellulose, hemicellulose, starch and proteins. Fourteen of the isolates produce antimicrobial molecules against the Gram-positive bacteria Micrococcus luteus. Analysis of seven strains led us to identify the production of a wide number of compounds including streptanoate, alpiniamide A, alteramides A and B, coproporphyrin III, deferoxamine, demethylenenocardamine, dihydropicromycin, nocardamine, picromycin, surugamides A, B, C, D and E, tirandamycins A and B, and valinomycin. A significant number of other compounds, whose molecular formulae are not included in the Dictionary of Natural Products (DNP), were also present in the extracts analyzed, which opens up the possibility of identifying new active antibiotics. Molecular identification of ten of the isolated bacteria determined that six of them belong to the genus Streptomyces, two of them are included in the genus Amycolatopsis and two in the genus Nocardiopsis.

Evidencia de actividad feromonal de contacto en Cerambyx welensii Küster y compuestos candidatos

Este trabajo analizó la existencia potencial de feromona sexual de contacto en Cerambyx welensii. Muestras de élitros y protórax (micro extracción en fase sólida) de ambos sexos se analizaron mediante CG-MS. Para confirmar la existencia de feromona de contacto en la cutícula de las hembras, se estudió la respuesta de machos de C. welensii frente a: hembras intactas, hembras muertas, hembras sometidas a extracción hexánica de lípidos cuticulares y hembras recubiertas de su propi extracto hexánico cuticular. Se encontraron 44 hidrocarburos cuticulares en élitros y 17 en protórax. Los mismos 6 compuestos comprendieron en conjunto, tanto en élitros como en protórax, entre el 68.1% (élitros de machos) y el 85.4% (protórax de hembras) del contenido lipídico total. Ninguno de los compuestos resultó específico de las hembras, pero se encontraron diferencias entre sexos en la presencia relativa para algunos compuestos. Los compuestos candidatos para actuar como feromona de contacto podrían localizarse tanto en élitros como en protórax, pudiendo actuar como componentes mayoritarios (abundancias relativas >17% en MEFS) el 11-Me-C29, C27, 2-Me-C26 y 11/13-Me-C27; como componentes minoritarios (abundancia relativa <2.5%) podrían ser candidatos el 11/12/13-Me-C26 y el C28. La mayoría de los machos (82%) mostró la secuencia de cópula característica en Cerambycidae: Contacto antenal – Giro - Lamido – Arqueo abdominal. La retirada de componentes cuticulares redujo fuertemente el interés de los machos (lamido y arqueo abdominal: <5%); la restitución de los extractos hexánicos devolvió la respuesta positiva en un 22% de los casos, indicando que la feromona de contacto se encontraba en el extracto cuticular.

Primera aproximación al estudio de la actividad fisiológica en Quercus suber con alta presencia de Cerambyx welensi Küster

La incidencia de Cerambyx welensii en Quercus suber es un factor clave en el decaimiento de árboles en las dehesas. Las pautas de selección de hospedantes por C. welensii son poco conocidas; entre otros factores, los volátiles de plantas se consideran claves en la localización de hospedantes en cerambícidos. En el presente trabajo estudiamos algunas características morfológicas de los árboles, así como la variación a corto plazo en la actividad fisiológica en Q. suber con distintos niveles de presencia de adultos de C. welensii. Nuestro objetivo fue analizar si la actividad fisiológica de Q. suber en condiciones de estrés veraniego podría variar entre árboles con distinta preferencia por C. welensii. Se estudiaron 36 Q. suber (18 árboles muy frecuentados por C. welensii; 18 sin avistamientos del insecto), en los cuales se midió la fotosíntesis neta, conductancia estomática y transpiración durante un período previo e incluyendo el inicio de vuelo diario de C. welensii (19:00 – 21:20 h); se analizó además el perímetro y la superficie de proyección de copa de los árboles. Los árboles con C. welensii exhibieron tasas fotosintéticas más altas (1.5–2.15 veces) que los árboles sin avistamientos del insecto entre las 19:35 y las 20:45, así como mayor perímetro y menor cociente superficie de proyección de copa a perímetro. Los resultados sugieren que tanto los ajustes fisiológicos bajo estrés ambiental (influyendo en el patrón de emisión de monoterpenos) como las características morfológicas de los árboles podrían tener un efecto en la selección intraespecífica de hospedantes por C. welensii.

DNA barcoding of large oak-living cerambycids: diagnostic tool, phylogenetic insights and natural hybridization between Cerambyx cerdo and Cerambyx welensii (Coleoptera: Cerambycidae)

Three large saproxylic cerambycids with different pest/legal status co-occur in the Iberian oak woodlands, Cerambyx welensii (Cw), Cerambyx cerdo (Cc) and Prinobius myardi (Pm): Cw is an emerging pest, Cc is a protected but sometimes harmful species and Pm is a secondary/minor pest. A precise taxonomic diagnosis is necessary for research, management or protection purposes, but may be problematic mainly because Cw and Cc larvae are morphologically indistinguishable. To resolve this constraint, we genotyped adults, larvae and eggs collected over a wide geographical range using the mitochondrial barcoding of the cytochrome c oxidase subunit I (COI). A Neighbour-Joining tree phylogram revealed three distinct clusters corresponding to Cw, Cc and Pm. We further first sequenced for Cw and Cc two mitochondrial (12S rRNA and 16S rRNA) and one nuclear (28S rRNA) gene fragments. For the first two genes, interspecific divergence was lower than in COI, and for the 28S (lower mutation rate), the two species shared identical haplotypes. Two approaches for species delimitation (General Mixed Yule Coalescent (GMYC), Barcode Index Number (BIN)) confirmed the species distinctiveness of Cc and Cw. The Bayesian COI gene tree showed a remarkable genetic divergence between Cc populations from Iberia and the rest of Europe. Such divergence has relevant taxonomic connotations and stresses the importance of a wide geographical scale sampling for accurate DNA barcoding species identification. Incongruities between morphology/lineage and COI barcodes in some individuals revealed natural hybridization between Cw and Cc. Natural hybridization is important from a phylogenetic/evolutionary perspective in these cerambycids, but the prevalence of (and the behavioural/ecological factors involved in) interspecific cross-breeding remain to be investigated.

Reproductive traits and number of matings in males and females of Cerambyx welensii (Coleoptera: Cerambycidae) an emergent pest of oaks

The longhorn beetle Cerambyx welensii is an emerging pest involved in oak decline episodes, whose damage is increasingly reported in dehesa open woodlands. Knowledge of the reproductive biology of C. welensii is a crucial goal due to its new pest status. In this study, we assess the reproductive traits of both sexes in the laboratory (25°C and 60% relative humidity ). In females, body length was 44.9 ± 0.9 mm (mean ± SE), fecundity 132 ± 12 eggs, fertility 70 ± 1 %, longevity 70 ± 3 days, preoviposition period 2 ± 0.2 days, oviposition period 44 ± 3 days and postoviposition period 19 ± 3 days. Fecundity was positively correlated with female size, longevity and oviposition period. Daily fecundity was 3.0 ± 0.2 eggs/day and showed a fluctuating synovigenic pattern with a slight decreasing trend over time. Egg length was 4.24 ± 0.01 mm and egg volume 8.14 ± 0.04 mm3. Egg size was correlated with female size but the relative size of eggs was larger in smaller females. Incubation time was 13.9 ± 0.1 days and hatching did not depend on egg size. Neonate size was positively correlated with egg length. Females were polyandrous (more than 20 lifetime matings) but multiple mating did not increase fecundity, fertility or longevity. In males, body length was 43.7 ± 0.6 mm and longevity 52 ± 3 days. Unlike with females, longevity was positively correlated with male size. Males were polygynous (up to 30 lifetime matings) but mating history did not affect male longevity. Rather to the contrary, long-lived males mated more times because they had more mating chances. Lastly, C. welensii reproductive traits were compared with those other Cerambycidae species and discussed from an adaptive perspective. Our data will be useful to improve management of C. welensii in order to prevent or mitigate its impact in dehesa woodlands and other oak forests.