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PREMISE: Of all orchid species described, 70% live on phorophytes. Trees offer a vital space with characteristics that influence the successful establishment and life cycle of orchids. Field inventory and distribution analysis suggest that phorophyte selection is biased to certain tree species that would serve as better hosts. Phorophyte bark is known as an important factor that influences this preference, but the chemical and physical properties of bark that contribute to creating a favorable space for orchids are still poorly understood. In this work, the effect of bark physical characteristics on phorophyte preference of tropical orchids was studied. METHODS:Orchids and their phorophytes were counted and identified along transects inside two natural reserves in Southeast Mexico. A rhytidome classification was used to describe the bark decoration patterns of the phorophytes. To quantify bark fissuring, we developed a new protocol based on image processing of light micrographs using free-access software. Bark topology characterization was complemented with scanning electronic microscopy. Maximum and minimum water content was also determined. RESULTS:Analyses of bark decorations and bark fissuring were not enough to explain the preference found for some tropical trees. In contrast, a positive relationship was found among water-storage capacity, bark porosity, and phorophyte preference. The host trees preferred by most orchids have bark with higher pore density and higher water retention after draining. CONCLUSIONS: Unexpectedly, the phorophytes preferred by orchids are not those with more fissured bark but those with a higher ability to retain minimum water content after draining, which is a bark property positively correlated with higher pore density. Our data indicate that the bark microenvironment, determined by topology and water storage capacity, has a pivotal role in phorophyte specificity, a key factor that affects orchid diversity and distribution in the world.

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Gall (Trioza rusellae Tuthill) insect identification in AbstractT he insect Trioza rusellae Tuthill (Hemiptera-Triozidae) produces galls on the leaves of the Ramon (Brosimum alicastrum Swartz) tree, species with high nutritional value of the Peninsula of Yucatan. The insect was isolated and identified from collections in the municipalities of Muna and Sacalum, Yucatán. Five to 10 years old trees were sampled selecting branches with leaves showing galls. The samples were placed in plastic bags and taken to the laboratory, and placed in entomological cages. Adult insects were collected using a manual vacuum, while galls were dissected to collect the nymphs directly with a brush (0001). The samples were preserved in alcohol (70 %) and in fixative formalin-alcohol-water (FAW). Nymphs and adult insects from the alcohol samples were mounted and observed on a stereoscopic microscope. The samples in FAW were processed and observed under a scanning electron microscope (SEM). As a result, photographs were obtained and development phases of T. rusellae were identified by entomological keys. Resumen E l insectoTrioza rusellae Tuthill (Hemiptera-Triozidae) produce agallas en las hojas del árbol de ramón (Brosimum alicastrum Swartz), especie con alto valor nutricional de la península de Yucatán. El insecto fue aislado e identificado a partir de colectas en los municipios de Muna y Sacalum, Yucatán. Los árboles de cinco a 10 años de edad se muestrearon seleccionando ramas con hojas que presentaban agallas. Las muestras se colocaron en bolsas de plástico y se trasladaron al laboratorio confinándolas en jaulas entomológicas. Los adultos se recolectaron con un aspirador manual, mientras que las agallas se disectaron para colectar las ninfas directamente con un pincel (0001). Las muestras se conservaron en alcohol (70 %) y en fijador formol-alcohol-agua (FAA). Las ninfas y adultos de las muestras en alcohol se montaron y observaron en el microscopio estereoscópico. Las muestras en FAA se procesaron y observaron en el microscopio electrónico de barrido (MEB). Como resultado, se obtuvieron fotografías y se identificaron las fases de desarrollo de T. rusellae mediante claves entomológicas.Received: August 05, 2014 / Accepted: March 10, 2015. Palabras clave:Ramón, agallas, plaga, caracterización, microscopio electrónico de barrido.

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