h Huanglongbing, or citrus greening, is a devastating disease of citrus plants recently spreading worldwide, which is caused by an uncultivable bacterial pathogen, "Candidatus Liberibacter asiaticus," and vectored by a phloem-sucking insect, Diaphorina citri. We investigated the infection density dynamics of "Ca. Liberibacter asiaticus" in field populations of D. citri with experiments using field-collected insects to address how "Ca. Liberibacter asiaticus" infection density in the vector insect is relevant to pathogen transmission to citrus plants. Of 500 insects continuously collected from "Ca. Liberibacter asiaticus"-infected citrus trees with pathological symptoms in the spring and autumn of 2009, 497 (99.4%) were "Ca. Liberibacter asiaticus" positive. The infections were systemic across head-thorax and abdomen, ranging from 10 3 to 10 7 bacteria per insect. In spring, the infection densities were low in March, at ϳ10 3 bacteria per insect, increasing up to 10 6 to 10 7 bacteria per insect in April and May, and decreasing to 10 5 to 10 6 bacteria per insect in late May, whereas the infection densities were constantly ϳ10 6 to 10 7 bacteria per insect in autumn. Statistical analysis suggested that several factors, such as insect sex, host trees, and collection dates, may be correlated with "Ca. Liberibacter asiaticus" infection densities in field D. citri populations. Inoculation experiments with citrus seedlings using field-collected "Ca. Liberibacter asiaticus"-infected insects suggested that (i) "Ca. Liberibacter asiaticus"-transmitting insects tend to exhibit higher infection densities than do nontransmitting insects, (ii) a threshold level (ϳ10 6 bacteria per insect) of "Ca. Liberibacter asiaticus" density in D. citri is required for successful transmission to citrus plants, and (iii) D. citri attaining the threshold infection level transmits "Ca. Liberibacter asiaticus" to citrus plants in a stochastic manner. These findings provide valuable insights into understanding, predicting, and controlling this notorious citrus pathogen. H uanglongbing (HLB), or citrus greening, is one of the most serious diseases of citrus plants in many countries across Asia, Africa, and North and South America (1-5). This disease is caused by the phloem-inhabiting, noncultivable, and insect-vectored bacterial pathogens "Candidatus Liberibacter asiaticus" (Asia, North America, and Brazil), "Ca. Liberibacter africanus" (Africa), and "Ca. Liberibacter americanus" (Brazil) (6-8).The Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Liviidae) is the principal vector of "Ca. Liberibacter asiaticus" in Asia, North America, and Brazil (1-5). On the grounds that "Ca. Liberibacter asiaticus"-infected D. citri insects are primarily responsible for infection and spread of HLB among citrus plants, monitoring and investigation of the infection dynamics of "Ca. Liberibacter asiaticus" in field populations of D. citri are of pivotal importance (9-12). Furthermore, infection densities of "Ca. Liberibacter asiaticus" within vector in...

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A series of 3-oxygenated α-ionone analogs have been developed as highly specific male lures for the solanaceous fruit fly Bactrocera latifrons, a pest of solanaceous fruits. We compared the attractant and phagostimulant activities of analogs with or without (i) unsaturations at the 4,5- and/or 7,8-positions and (ii) oxygen moieties at the 3- and/or 9-positions of the ionone molecule. Since naturally occurring vomifoliol (V2) was found to induce a highly potent phagostimulant activity in B. latifrons males, related analogs including, dehydrovomifoliol (V1), 6-hydroxy-α-ionone (U1) and 6-hydroxy-α-ionol (U2) were synthesized to evaluate their attractant and phagostimulant activities. Synthetic V1, V2, U1 and U2 exhibited low attractant activity, but their phagostimulant activity was relatively high. Optical isomers of 3-oxo-7,8-dihydro-α-ionone (P3) and V1 were prepared to examine the stereochemical specificity of attractants. (+)-(6R)-P3 and (+)-(6S)-V1 exhibited the corresponding activities, while their respective antipodal enantiomers were found entirely inactive.