Modeling and dynamics of physiological and behavioral resistance of Asian citrus psyllid

A study of integrated pest management models with instantaneous and non-instantaneous impulse effects

The occurrence of pests and diseases during agricultural production affects the quality and quantity of agricultural products. It is important to evaluate the impact of various factors on pests to achieve optimal results of integrated pest management (IPM) during its implementation. In this paper, we considered the transient and non-transient effects of chemical control on pests and the effects on natural enemies at different times, and developed a corresponding pest control model. Detailed studies and comparisons were conducted for spraying pesticides either more or less frequently as compared to strategies for releasing natural enemies. The threshold conditions for global asymptotic stabilization of the pest extinction period solution was obtained. Using two-parameter and sensitivity analysis techniques, the parameters affecting the variation of the threshold were discussed. By comparing these two pest control strategies, we found the existence of optimal application and release frequencies. Finally, in order to control pests below the economic threshold level, the state-dependent pest model was numerically investigated. The results show that the presence or absence of chemical control of pests can depend on the values taken for the parameters in the model. Based on this information, pest control experts can make decisions about the best spraying time and the best release rate.

Overexpression of the Chemosensory Protein CSP7 Gene Contributed to Lambda-Cyhalothrin Resistance in the Bird Cherry-Oat Aphid Rhopalosiphum padi

Lambda-cyhalothrin is one of the most important pyrethroids used for controlling wheat aphids. Extensive spraying of lambda-cyhalothrin has led to the development of high resistance to this pyrethroid inRhopalosiphum padi. The mechanisms of resistance are complex and not fully understood. In this study, we found that a laboratory-selected strain of R. padi showed extremely high resistance to lambda-cyhalothrin and cross-resistance to bifenthrin and deltamethrin. The expression level of RpCSP7 was significantly elevated in the resistant strain compared to that in the susceptible strain. Knockdown of RpCSP7 increased the susceptibility of R. padi to lambda-cyhalothrin, whereas the susceptibility to bifenthrin and deltamethrin was not significantly changed. The recombinant RpCSP7 displayed a high affinity for lambda-cyhalothrin but no affinities to bifenthrin and deltamethrin. These findings suggest that the overexpression of RpCSP7 contributes to the resistance of R. padi to lambda-cyhalothrin. This study provides valuable insights into CSP-mediated insecticide resistance in insects.

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

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.