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The Asian citrus psyllid (Diaphorina citri Kuwayama) is the principal vector of 'Candidatus Liberibacter asiaticus' (CLas) associated with huanglongbing (HLB), the most serious citrus disease worldwide. New control measures including pesticides are urgently needed to combat HLB, especially to protect young or newly planted citrus trees from CLas-inoculation by vector psyllids. Here, we tested CLas-inoculation by D. citri adults (CLas-exposed, reared on infected plants) by feeding them for 7 d on excised healthy citrus leaves with dry residues of cyantraniliprole (Exirel), a novel insecticide, in comparison with fenpropathrin (Danitol 2.4EC), an insecticide commonly used against D. citri. Fewer adults settled (putatively feeding or probing) on leaves treated with cyantraniliprole than those treated with fenpropathrin or water controls. Also, psyllid adults died at a slower rate on leaves treated with cyantraniliprole than those treated with fenpropathrin, although the final cumulative mortality did not differ between the two treatments. In quantitative real-time polymerase chain reaction tests, 59.0-65.3% of the CLas-exposed psyllid adults were proven to be CLas-positive. Inoculation rates of CLas (using 10 adults per leaf) into untreated healthy citrus leaves (47.5-85%) were significantly higher than rates into leaves treated with cyantraniliprole or fenpropathrin (2.5-12.5%). Reduced inoculation rates to leaves treated with cyantraniliprole probably occurred as a result of reduced feeding or probing by D. citri. The excised leaf assay method, which took only a few weeks compared with up to a year or longer using whole plants, can be an effective tool for testing the effect of new pesticides or other treatments in reducing CLas inoculation or transmission by psyllid vectors., (Published by Oxford University Press on behalf of Entomological Society of America 2015. This work is written by a US Government employees and is in the public domain in the US.)

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is the primary vector of Candidatus Liberibacter asiaticus (Las) associated with huanglongbing, or citrus greening, the most devastating citrus (Citrus spp.) disease worldwide. Here, we developed a new "excised-leaf assay" that can speed up Las-inoculativity tests on Asian citrus psyllid from the current 3-12 mo (when using whole citrus seedlings for inoculation) to only 2-3 wk. Young adults of Asian citrus psyllid that had been reared on Las-infected plants were caged on excised healthy sweet orange [Citrus sinensis (L.) Osbeck] leaves for a 1-2-wk inoculation access periods (IAP), and then both psyllids and leaves were tested later by quantitative polymerase chain reaction (PCR). When single adults were tested per leaf, percentages of Las-positive leaves averaged 2-6% by using HLBaspr primers and 10-20% by using the more sensitive LJ900 primers. Higher proportions of Las-positive leaves were obtained with 1) higher densities of inoculating psyllids (5-10 adults per leaf), 2) longer IAPs, and 3) incubation of leaves for 1 wk postinoculation before PCR. Logistic regression analysis indicated a positive correlation between Las titer in Asian citrus psyllid adults tested singly and the probability of detecting Las in the inoculated leaves, correlations that can be very useful in epidemiological studies. Comparison between excised leaves and whole seedlings, inoculated consecutively for 1 wk each by one or a group of psyllids, indicated no significant difference between Las detection in excised leaves or whole plants. This new excised-leaf assay method saves considerable time, materials, and greenhouse space, and it may enhance vector relation and epidemiological studies on Las and potentially other Liberibacter spp. associated with huanglongbing disease.