Artificial release of marked adult Diaphorina citri, the insect vector of citrus greening disease, was performed in July 2007 (10,000 adults released, experiment 1) and October 2008 (1,000 adults released, experiment 2) to determine the association of the dispersal pattern with disease invasion risk. During the experimental periods, in experiment 1, the mean dispersal distances from the release point were 5-6 m and in experiment 2 they were 6-12 m. Further examination of the relationship between dispersal distance and season is needed. The number of released D. citri declined with increasing distance from the release point and did not change markedly with time. The center of distribution moved little during the experimental period. These results suggest that the adult D. citri barely moved once they had colonized a host plant within a few days after their release. Our results also suggest that the released D. citri moved with the wind. The diffusion coefficient was estimated at 7.23 from experiment 1, but random diffusion might be a poor descriptor of the dispersal of adult D. citri.

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Asian citrus greening disease (CGD) is caused by Candidatus Liberibacter asiaticus, transmitted by the Asian citrus psyllid, Diaphorina citri Kuwayama. An effective method for controlling the pathogen is currently unavailable; therefore, controlling psyllids is a more practical strategy for minimizing damage from CGD. However, ecological/ethological field studies on this insect are limited due to a lack of effective marking methods. This study examined the effectiveness of a marking method for psyllids using fluorescent powder (FZ-2803). Equal numbers of marked and unmarked psyllids were released at a distance of 2 m from a light. The collection of marked psyllids near the light was significantly lower than that of unmarked psyllids until 4 h after marking. After 5 h, no significant difference was observed. No significant differences in mortality were detected between the two groups during a 40-day period after marking. The persistence of a mark on the psyllid body was confirmed visually in the laboratory for 40 days. One hundred marked psyllids were released in an orange jasmine field (18 mϫ18 m). The marked insects were detected visually, and the proportion of marked insects was 30% after 20 days and 20% after 40 days. These results indicate that the marking method using fluorescent powder does not affect survival, and it can be used for ca. 5 weeks in the field.

The citrus psyllid Diaphorina citri Kuwayama transferred huanglongbing (HLB) are distributed in the southern Islands (Yaku, 30°20ЈN, 130°30ЈE) of Japan. To predict the northern limit of the spread of the insect, I examined temperature-dependent development and determined the developmental zero of the insects in a laboratory. Eggs and nymphs were reared at temperatures of 15.0 to 32.5°C at an interval of 2.5°C with 16L : 8D on shoots of orange jasmine, Murraya exotica L. Nymphs at 15.0°C fail to develop to adults, and the mortality of those at 32.5°C increased. The incubation period decreased at higher temperatures, varying 15.0 to 2.5 d. These nymphs became adults in 36.3 d at 15.0°C and in 10.7 d at 30°C, but 16.8 d at 32.5°C. The developmental zero and effective accumulative temperatures were 13.66°C and 46.93 d-degrees in the egg group, 11.56°C and 192.27 d-degrees in the nymph group, respectively. Based on these results and winter temperatures, the northern limit of nymphal overwintering of the psyllid in Japan was predicted: the northern limit may be off the southern shores of Kyushu Island, southern Japan, and ca. 31°N.

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