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An unprecedented plant health emergency in olives has been registered over the last decade in Italy, arguably more severe than what occurred repeatedly in grapes in the United States in the last 140 years. These emergencies are epidemics caused by a stealthy pathogen, the xylem-limited, insect-transmitted bacterium Xylella fastidiosa. Although these epidemics spurred research that answered many questions about the biology and management of this pathogen, many gaps in knowledge remain. For this review, we set out to represent both the U.S. and European perspectives on the most pressing challenges that need to be addressed. These are presented in 10 sections that we hope will stimulate discussion and interdisciplinary research. We reviewed intrinsic problems that arise from the fastidious growth of X. fastidiosa , the lack of specificity for insect transmission, and the economic and social importance of perennial mature woody plant hosts. Epidemiological models and predictions of pathogen establishment and disease expansion, vital for preparedness, are based on very limited data. Most of the current knowledge has been gathered from a few pathosystems, whereas several hundred remain to be studied, probably including those that will become the center of the next epidemic. Unfortunately, aspects of a particular pathosystem are not always transferable to others. We recommend diversification of research topics of both fundamental and applied nature addressing multiple pathosystems. Increasing preparedness through knowledge acquisition is the best strategy to anticipate and manage diseases caused by this pathogen, described as "the most dangerous plant bacterium known worldwide.", Competing Interests: The author(s) declare no conflict of interest.

The red streaked leafhopper, Balclutha rubrostriata (Melichar) (Hemiptera: Cicadellidae), is an invasive insect from southeastern Asia that is known to be a vector of the phytoplasma that causes Sugarcane White Leaf Disease (SCWL). Sugarcane is a vital crop for the United States and is being considered as a biofuel source. The purpose of this survey was to determine whether B. rubrostriata has established populations in Texas and Louisiana, USA; and, if established, to estimate its range expansion. The gulf coast region of Texas, east Texas, and 2 southwestern parishes of Louisiana were surveyed for the red streaked leafhopper. Samples of the leafhopper were collected in all Gulf Coast regions and the majority of east Texas counties. However, it was only collected in one Louisiana parish. The leafhopper appears to be closely associated with an invasive grass, King Ranch Bluestem, Bothriochloa ischaemum (L.), throughout much of its present range in the United States, and it is now common along much of the Texas Gulf Coast and is moving into Louisiana. [ABSTRACT FROM AUTHOR]

Compared to human- and wildlife-transmitted pathogens, less emphasis has been placed on developing models of plant pathogen transmission by insects. Here, we describe the transmission ecology of the bacterium Xylella fastidiosa Wells et al., the causal agent of Pierce’s disease in grapevines, by its leafhopper vectors. First, we performed a meta-analysis of transmission studies of X. fastidiosa by its two most important vectors in the Western USA, the invasive glassy-winged sharpshooter, Homalodisca vitripennis Germar, and the native blue-green sharpshooter, Graphocephala atropunctata Signoret (both Hemiptera: Cicadellidae). The importance of vector number, pathogen acquisition period, and inoculation access period (IAP) for transmission differed between the two species. We fit these transmission datasets to two biologically derived transmission models, i.e., a binomial and a Poisson probability model. The Poisson model provided substantially better fit and produced estimates of H. vitripennis transmission efficiency that were dramatically lower than for G. atropunctata. We also conducted a separate pair of experiments that decoupled vector number from IAP. These experiments supported the results of the meta-analysis. Interestingly, high vector loads not only increased transmission rate, but also shortened X. fastidiosa incubation period in grapevines. This work provides quantitative estimates of transmission of an economically important pathogen that is analogous to risk models for arthropod-vectored human and wildlife diseases. In addition, this work suggests that heterogeneous vector loads may accelerate the disease cycle, increasing the potential for secondary spread in vineyards. [ABSTRACT FROM AUTHOR]