Modeling Study of the Effects of Ageratum conyzoides on the Transmission and Control of Citrus Huanglongbing

Abstract

Ageratum conyzoides (A. conyzoides) is commonly found or intentionally planted in citrus orchards due to its ability to provide habitat and breeding grounds for the natural enemies of citrus pests. This study aims to expand from a switching Huanglongbing model by incorporating the effects of A. conyzoides, vector preferences for settling, and pesticide application intervals on disease transmission. Additionally, we establish the basic reproduction number R0 and its calculation for a general switching compartmental epidemic model. Theoretical findings demonstrate that the basic reproduction number serves as a threshold parameter to characterize the dynamics of the models: if R0<1, the disease will disappear, whereas if R0>1, it will spread. Numerical results indicate that the recruitment rate of A. conyzoides not only affects the spread speed of Huanglongbing but also leads to paradoxical effects. Specifically, in cases of high infection rates, a low recruitment rate of A. conyzoides can result in a decrease, rather than an increase, in the basic reproduction number. Conversely, a high recruitment rate can accelerate the spread of Huanglongbing. Furthermore, we show how different vector bias and pesticide spraying periods affect the basic reproduction number.