Validation of reference genes for quantitative PCR in the forest pest, Ips calligraphus

The six-spined ips, Ips calligraphus, is a North American bark beetle that can exploit most eastern North American Pinus species and can cause mortality. Biotic and abiotic disturbances weaken trees, creating breeding substrate that promotes rapid population growth. Management historically relied on silvicultural practices, but as forests become increasingly stressed, innovative management is needed. Manipulation of the cellular RNA interference (RNAi) pathway to induce gene silencing is an emerging means of insect suppression, and is effective for some bark beetles. Quantitative PCR (qPCR) is a powerful tool for analysis of gene expression, and is essential for examining RNAi. To compare gene expression among individuals, stably expressed reference genes must be validated for qPCR. We evaluated six candidate reference genes (18s, 16s, 28s, ef1a, cad, coi) for stability under biotic (beetle sex, developmental stage, and host plant), and abiotic (temperature, photoperiod, and dsRNA exposure) conditions. We used the comprehensive RefFinder tool to compare stability rankings across four algorithms. These algorithms identified 18s, 16s, and 28s as the most stably expressed. Overall, 16s and 28s were selected as reference genes due to their stability and moderate expression levels, and can be used for I. calligraphus gene expression studies using qPCR, including those evaluating RNAi.

Registro de escarabajos descortezadores (Curculionidae: Scolytinae) en el Bosque La Primavera, Jalisco

Se obtuvieron los primeros registros de Scolytinae para el Bosque La Primavera, Jalisco (área natural protegida), con 11 especies y seis géneros, así como su distribución altitudinal. Los insectos fueron capturados mediante trampas, dos de ellas tipo Lindgren de 10 embudos (cebadas con feromonas de Dendroctonus ponderosa e Ips typographus), las cuales se instalaron en vegetación de pino-encino; las otras tres fueron tipo embudo metálica (cebadas con alcohol etílico al 70 %, anticongelante y en el interior de la trampa se colocó thinner), se ubicaron en vegetación de pino, de encino y una más en una asociación de acacias. Las cinco trampas se distribuyeron a diferente gradiente altitudinal: de 1 380 a 1 580 msnm. El grupo más abundante, con respecto a especies fueron Xyleborus affinis, X. ferruginueus, X. volvulus y Gnathotrichus perniciosus. De esta colecta se presentan tres nuevos registros para el estado de Jalisco: Hylurgops subcostulatus alternans, Premnobius cavipennis y Xyleborus horridus; y locales: Ips calligraphus e I. cribicollis. La trampa cinco presentó la mayor captura, con ocho especies (cebada con alcohol etílico al 70 %), seguida por la trampa uno con siete (cebada con feromonas); los dos tipos de trampas demostraron ser eficientes para la captura de insectos descortezadores.

Ips calligraphus. [Distribution Map].

A new distribution map is provided for Ips calligraphus (Germar) sens. lat. Coleoptera: Scolytidae. Hosts: most Pinus spp. within its range, especially thick-barked species such as Pinus ponderosa and P. strobus. Information is given on the geographical distribution in Asia (Philippines), Africa (South Africa), North America (Canada (Nova Scotia, Ontario, Quebec, Saskatchewan), Mexico, USA (Alabama, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Illinois, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Virginia, West Virginia, Wisconsin, Wyoming)), Central America and Caribbean (Cuba, Dominican Republic, Guatemala, Haiti, Honduras, Jamaica, Nicaragua).

Impact of Platysoma parallelum and Plegaderus transversus (Coleoptera: Histeridae) Predation on Developing Ips calligraphus and Ips grandicollis (Coleoptera: Scolytidae) Brood

As a group, arthropod natural enemies have been shown to substantially reduce within-tree pine bark beetle populations. However, little is known about the impacts of individual species on bark beetle mortality. In a controlled laboratory study, we measured the effects of two predaceous histerid species, Platysoma parallelum (Say) and Plegaderus transversus (Say), on Ips calligraphus (Germar) and Ips grandicollis (Eichhoff) brood mortality. Platysoma parallelum was found to have a greater impact on I. grandicollis mortality than Ple. transversus when only one histerid and prey species were present. No significant differences in I. calligraphus mortality were observed for either of the two histerid species. More I. grandicollis brood was killed per introduced Pla. parallelum adult than per introduced Ple. transversus adult likely as a result of the larger size and biomass requirements of Pla. parallelum. The results of this experiment indicate that histerids, by themselves, have the ability to lower within-tree bark beetle populations and could have potential use in a bark beetle biological control program.