Morphological and Phylogenetic Analyses Reveal a New Species of Ceratocystiopsis (Ophiostomataceae, Ophiostomatales) Associated with Ips subelongatus in Inner Mongolia (China) with Weak Host Pathogenicity

Ophiostomatoid fungi are known for their associations with bark beetles, and some species are important sources of tree diseases. Ceratocystiopsis is a genus of the ophiostomatoid fungi in order Ophiostomatales. The shortage of DNA barcodes for many species in this genus has resulted in the presence of many unnamed cryptic species. In this study, Ceratocystiopsis subelongati sp. nov. associated with Ips subelongatus infesting Pinus sylvestris var. mongolica in Inner Mongolia, China, was identified and described based on phylogenetic inference of multi-gene DNA sequences and morphological characteristics. The species is characterized by a hyalorhinocladiella- to sporothrix-like asexual state and an optimal growth temperature of 30 °C. Artificial inoculation tests in the field showed that it is mildly pathogenic to five-year-old larch trees, the main host of I. subelongatus. It is also the first described Ceratocystiopsis species associated with I. subelongatus in China. This discovery should provide new avenues for studying the symbiosis between bark beetles and ophiostomatoid fungi.

Ophiostomatoid fungi including a new species associated with Asian larch bark beetle Ips subelongatus, in Heilongjiang (Northeast China)

Ips subelongatus (Coleoptera, Scolytinae) is an important bark beetle species that infests Larix spp. in Asia. Individuals of this beetle are vectors of ophiostomatoid fungi, on their exoskeletons, that are transmitted to infested trees. In this study, the symbiotic assemblage of ophiostomatoid fungi associated with I. subelongatus in Northeast China was studied. Fungal isolates were identified based on their morphological characters and sequences of ITS, beta-tubulin, elongation factor 1-alpha and calmodulin gene regions. In total, 48 isolates were collected and identified, residing in six taxa. These included a novel species, described here as Ophiostoma gmelinii sp. nov.

Forecasting Spring Flight of Ips subelongatus (Coleoptera: Curculionidae: Scolytinae) in Japanese larch Larix kaempferi (Pinales: Pinaceae) Forests in the Republic of Korea

Ips subelongatus is a species of bark beetle experiencing population outbreaks in Korea. In this study, a predictive model and empirical prediction were used to forecast the spring flight of these beetles in Japanese larch forests. The number of beetles caught in pheromone traps was investigated in larch forests thinned in 2009, 2010, 2012, or 2013. Data from the sites thinned in 2009, 2010, or 2012 were used in the predictive model based on a degree-day model that was validated using data from the site thinned in 2013. The lower threshold temperature for flight (LTF) and a thermal sum for the spring flight of I. subelongatus were estimated. The empirical prediction that beetles initiate their flight when daily maximum temperatures reach 16 or 20°C was tested using daily maximum temperature and the beetles caught. The LTF was estimated as 5.97°C, with 42.95 degree-days required for initiation of spring flight. The median flight dates were estimated with a discrepancy from 1 to 3 d by the predictive model. Using the empirical prediction, differences between the day when daily maximum temperature reached 16 or 20°C and flight peak days ranged from 4 to 45 d. These results demonstrate that the predictive model is more suitable than the empirical prediction for predicting the spring flight of I. subelongatus. Overwintering I. subelongatus adults seem to need to gain a determined thermal sum before initiating spring flight rather than merely waiting for the daily maximum temperature to exceed a critical temperature.

Ophiostoma olgensis, a new species associated with Larix spp. and Ips subelongatus in northern China

A new ophiostomatoid species, Ophiostoma olgensis sp. nov., isolated from Larix olgensis and Larix gmelini infested by Ips subelongatus in northern China, is described and illustrated. The fungus produces abundant short-necked perithecia in phloem as well as on artificial substrates. The short-necked perithecia are characteristic of the Ophiostoma minus complex and more specifically, of Ophiostoma kryptum, isolated from European larch. However, O. olgensis can be distinguished from O. kryptum on the basis of combined morphological traits and phylogenetic data from ITS, partial β-tubulin, EF-1α, and actin gene region analyses of single-spore isolates. The most obvious morphological differences between both species are the asexual forms and the conidial morphology. The pathogenicity of O. olgensis and O. kryptum was evaluated in situ on local mature Larix spp. by stem inoculation. All inoculations of O. olgensis and O. kryptum resulted in serious lesions on the inner bark, and thus the new species is considered to be a pathogen on Larix spp. (L. olgensis, L. gmelini, L. principis-rupprechtii and L. kaempferi ).