**3.3 Attempts to simulate more realistic scenarios**

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

Development of an Individual-Based Simulation Model

although we developed the model for HLB.

**4. Conclusion** 

**5. Acknowledgment** 

for the parameter estimation.

November 1992

**6. References** 

for the Spread of Citrus Greening Disease by the Vector Insect *Diaphorina citri* 99

This chapter described the development of an individual-based modelling technique to simulate disease-spread dynamics. Our model was able to provide parameters for each individual citrus tree and the respective vector insect, and thereby to examine diseasespread dynamics in the simulation field by calculating the cumulative results of the individual behaviors. This model can be applied to many diseases vectored by insects,

Our simulated results suggested that both delaying the transition from latent period (*LP*) to infectious period (*IP*), and removing infectious (*IP*) trees, suppressed the spread rate of HLB in an orchard. Additionally, the results of our a preliminary trail suggested that cooperative control of *D. citri* on the part of orchard owners in a given area*,* to reduce the number of

Part of this study was conducted as part of the collaborative research project between the Japan International Research Center for Agricultural Sciences (JIRCAS) and the Southern Horticultural Research Institute of Vietnam (SOFRI). In addition, part of this work was supported by KAKENHI (23780052). We thank Mr. Masato Shimajiri, Mr. Masakazu Hirata, and the staff of the Technical Support Section of TARF/JIRCAS for their help in managing and maintaining the experimental field for estimation of the parameters. We are grateful to Ms. Aya Yano, Mr. Kenji Mishima, Mr. Hiroyuki Murota, Ms. Kiyomi Toume and Satoshi Kawate for their help in producing the released insects and controlling our plant conditions

Aubert, B. (1987). *Trioza erytreae* del Guercio and *Diaphorina citri* Kuwayama (Homoptera:

*Organization of Citrus Virologists (IOCV)*, pp. 276-278, China, November 2005 Buitendag, C. H. & von Broembsen, L. A.(1993). Living with Citrus Greening in South

Bové, J. M., Garnier, M., Ahlawat, Y. S., Chakraborty, N. K. & Varma, A. (1993). Detection of

Capoor, S. P., Rao, D. G. & Viswanath, S. M. (1974). Greening disease of citrus in the Deccan

possible control strategies. *Fruits, Vol.* 42, pp.149-162, ISSN 0248-1294 Aubert, B., Grisoni, M., Villemin, M. & Rossolin. G. (1996). A case study of huanglongbing

*Virologists (IOCV)*, pp. 269-273, India, November 1992

*(IOCV)*, pp. 43-49, Swaziland, August 1972

Psylloidea), the two vectors of citrus greening disease: Biological aspects and

(greening)control in Réunion, *Proceedings of 13th Conference of the International* 

Africa, *Proceedings of 12th Conference of the International Organization of Citrus* 

the Asian Strains of the Greening BLO by DNA-DNA Hybridization in Indian Orchard Trees and Malaysian *Diaphorina citri* Psyllids, *Proceedings of 12th Conference of the International Organization of Citrus Virologists (IOCV)*, pp. 258-263, India,

Trap Country and its relationship with the vector, *Diaphorina citri* Kuwayama, *Proceedings of 6th Conference of the International Organization of Citrus Virologists* 

virulent individuals, may be effective in suppressing the spread rate of HLB.

that had migrated from an infected orchard into the newly planted orchard would die after feeding (if an individual was virulent it might transmit HLB, but would not reproduce on the tree). After this period, individuals migrating from the infected orchard would reproduce in the newly planted orchard. The number of newly infected trees was lower in the plantings treated with systemic pesticide than in those with the negative controls. We concluded that treatment with systemic pesticide was effective in suppressing the spread rate of HLB in a newly planted orchard, and the effect was definitive when the virulent *D. citri* migrated from a nearby orchard (Fig. 9). Part of this study have been reported in Kobori et al. (2011c).

Dashed line, negative control (did not treat systemic pesticide); soiled line, treated with systemic pesticide (effective for 24*t*). Number of initial *H* trees in the simulated field was 256. No. of newly infected trees = *LP+IP+D* (excluding initial *D* trees). Modified from Kobori et al. (2011).

Fig. 9. Effects of systemic pesticide to suppress HLB in the field.

Although these results generated valuable suggestions, there was a problem in our simulated conditions. In a number of replications, extinction of the vector insect occurred. In actual observation, even insects not found in a given season could be found in later observations. One cause of this may be the closed nature of our simulation system. In reality, vector insects could immigrate into the field. Currently, we are expanding the model to incorporate this possibility. In addition, the dispersal kernel was developed for calculations of single-field behavior. We must revise the kernel to simulate larger scenarios, such as those involving multiple, separated fields.
