**3.1 Spread of HLB in a field under default conditions**

We simulated HLB spread under default conditions. Field size was set at *L*, *M* = 100. Healthy trees (*H*) were distributed at the center of the field (*L*, *M* = 20). The remaining trees were *D*. Then, 100 virulent vector insects were distributed at the center of the *H* field. We set the model calculation period for 84 months.

of 1-*Dl*) are integrated into the next generation. There is insufficient previous research to provide estimates for these parameters, and we could not estimate their value by certain observation or experiment. Thus, we roughly estimated these parameters at *Dm*: 0.7 and *Dl*: 0.9 by speculative inference from life-table analysis and our own limited observation in this

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Empty and solid circles indicate 10,000 adults and 1,000 adults released, respectively. The two arrows (solid: 10,000 adults; dashed: 1,000 adults) indicate the composite wind vectors over the experimental periods, as calculated from the daily dominant wind directions. The average velocities were 2.42 m/s in the case of 10,000 adults released, and 3.98 m/s in the case of 1,000 adults released. From Kobori et al.

Fig. 5. Center of distribution, over the experimental period, of insects released at the zero

We simulated HLB spread under default conditions. Field size was set at *L*, *M* = 100. Healthy trees (*H*) were distributed at the center of the field (*L*, *M* = 20). The remaining trees were *D*. Then, 100 virulent vector insects were distributed at the center of the *H* field. We set

**3. HLB disease-spread simulation using the model 3.1 Spread of HLB in a field under default conditions** 

the model calculation period for 84 months.

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report (e.g. Mead, 1977; Tsai et al., 2002).

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(2011b).

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Within 12*t*, more than 10 newly infected trees had appeared in the given field (Fig. 6 (a)). The spread speed increased with time (Fig. 6 (b)). By the end of the calculation period, more than half of the *H* trees had changed status to *LP, IP* or *D*.

Blue dot indicates Latent Period (*LP*); red: Infectious Period (*IP*), black: Dead (*D*). Healthy (*H*) trees are not shown. Solid line: number of trees newly infected; dotted line: number of initial *H* trees in the simulated field (1,681 trees).

Fig. 6. (a) Snapshots of tree-status distribution for *t*=12, 24, 36, 48, 56, 68, 72, 84. (b) Number of trees newly infected in the field over time.

Development of an Individual-Based Simulation Model

No. of newly infected trees

spread of HLB in a field.

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for the Spread of Citrus Greening Disease by the Vector Insect *Diaphorina citri* 97

trees was more than 1,000 (Fig. 8). When we removed the *IP* trees 24*t* after their status change, the number of newly infected trees was almost same as under the default condition. However, when we removed the *IP* trees 9*t* after their status change, the number of newly infected trees decreased relative to the default condition. Moreover, when we removed the *IP* trees 6*t* after their status change, the number of newly infected trees barely increased. We may thus predict that the removal of infectious trees will be efficacious in preventing the

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Black dashed line: no removal; red dashed line: removal 24*t* after infection; green dash-dotted line: 12*t*; blue dash-dotted line: 6*t.* Black dashed line is number of initial *H* trees in the simulated field

The vector insect population follows seasonal trends (e.g., Nakahira et al., 2011). Thus, we established high/low reproductive periods and conducted the simulation. The number of newly infected trees increased with time without immigration of virulent vector insects. The model forecast that more than 80% of trees were infected with HLB by 84*t*. Hence, we suggest that the use of disease-free seedlings offers a fundamental technique for preventing HLB spread in an orchard. Additionally, we estimated the suppression of the HLB spread rate through systemic pesticide treatment in a newly planted orchard. Several reports have indicated that systemic pesticide treatment causes high mortality rates in *D. citri* (e.g., Ichinose et al., 2010). We assumed that pesticide applied in the new orchard would be effective for two years. Hence, we assumed that, until 24*t* after planting, 100% of the insects

(1,681 trees). No. of newly infected trees = *LP+IP+D* (excluding initial *D* trees).

Fig. 8. Effects of infectious tree (*IP*) removal in the field.

**3.3 Attempts to simulate more realistic scenarios** 

*t*
