Effect of fluensulfone and fluopyram on the mobility and infection of second-stage juveniles of Meloidogyne incognita and M. javanica.

BACKGROUND: Fluensulfone and fluopyram are new nematicides whose mode of action is not fully understood. Differences in the nematicidal activity of these compounds among two Meloidogyne incognita populations and a Meloidogyne javanica population, and the effect of sublethal exposure to the nematicide on their infection process were studied in vitro. RESULTS: The M. incognita populations were more sensitive to fluensulfone than M. javanica, whereas M. javanica was more sensitive to fluopyram. A more than 10-fold difference in median lethal concentration (LC50 ) was observed between the M. incognita populations after 17-h exposure to fluensulfone. Exposure of M. incognita and M. javanica to 4 mg L-1 fluopyram for 48 h resulted in irreversible immobilization, whereas lower concentrations or 17-h exposure to fluopyram caused reversible immobilization. Pre-exposure of M. javanica to fluensulfone at sublethal concentrations reduced the number of juveniles attracted to root tips and caused smaller galls. Pre-exposure to fluopyram delayed the nematodes' attraction. Presence of fluopyram in a Pluronic gel at concentrations that immobilized the nematodes in water showed no or only slight inhibition of the nematodes' attraction to root tips and gall formation. CONCLUSION: Different sensitivities to nematicides were observed among Meloidogyne species and populations. Sublethal exposure to fluensulfone reduced nematode attraction to root tips and infection. Pluronic gel negatively affected nematicidal activity, especially for fluopyram. © 2019 Society of Chemical Industry.

Prevalence of the symbiont Cardinium in Culicoides (Diptera: Ceratopogonidae) vector species is associated with land surface temperature.

Prevalence of infection by bacterial symbionts may reflect their interactions with the host and has been shown to be correlated with environmental factors. Yet, it is still unclear whether infection by symbionts is determined by environmental factors affecting the early or imago stage of the host. Here, we identified and localized the symbiont Candidatus Cardinium hertigii (Bacteroidetes) in sympatric Culicoides biting midge species, examined its abundance, and studied its association with environmental factors. The prevalence of adult infection differed, with 50.7% from C. imicola, 31.4% from C. oxystoma, and 0% from C. schultzei gp., although phylogenetic analyses showed that Cardinium in these species is almost identical. In addition, prevalence of infection differed between climate regions, with lowest prevalence in the arid region and highest prevalence in the Mediterranean region. Multivariate linear regression analysis of Cardinium prevalence together with climatic and satellite imagery data-derived environmental variables revealed that infection prevalence is significantly associated with land surface temperature and explained up to 89.7% of infection prevalence variability. These findings suggest that the observed variation of Cardinium infection of the imago stage of Culicoides may be influenced by environmental conditions during the latter's early developmental stages.

Molecular identification, phylogenetic status, and geographic distribution of Culicoides oxystoma (Diptera: Ceratopogonidae) in Israel.

Culicoides oxystoma (Diptera: Ceratopogonidae) is an important vector species, reported mainly from Asia, with high potential to transmit viral diseases affecting livestock. In Japan, many arboviruses have been isolated from C. oxystoma, suggesting it as a key player in the epidemiology of several Culicoides-borne diseases. Over the years, C. oxystoma has also been reported in the Middle East region, including Israel. In this region, however, C. oxystoma cannot be easily distinguished morphologically from its sibling species included in the Culicoides schultzei complex. We therefore used genomic data for species identification and phylogeny resolution. Phylogenetic analyses based on internal transcribed spacer 1 (ITS-1) of ribosomal DNA and the mitochondrial gene encoding cytochrome oxidase subunit I (COI) showed that C. oxystoma from Israel is closely related to C. oxystoma from Japan. Using differential probing PCR, we showed that C. oxystoma is distributed all over the country, especially in Mediterranean climate regions. Culicoides oxystoma is less common or even absent in arid regions, while the other genetic cluster of C. schultzei complex was found only in the east of the country (mostly arid and semiarid regions). The molecular finding of C. oxystoma in wide geographical regions, together with its high proportion in the general Culicoides population and its vectoring potential, imply that it may be an important vector species in the Middle East.