# A Laser Irradiation Method for Controlling _Pieris rapae_ Larvae
## 1 Introduction  
Adult _Pieris rapae_ (L.) (Lepidoptera: Pieridae) is one of the most numerous and tenacious butterflies in the world [1], and the larvae are a notorious pest of Cruciferae. In some serious cases, the larvae consume all the leaves and can even cause soft rot [2]. At present, chemical control remains the main control method for these larvae. The long-term use of chemical pesticides has caused harm to humans and the environment and forms a vicious cycle [3]. Therefore, the identification of an eco-friendly control method is urgently needed to support the demand for a greater quantity cruciferous plant of higher quality.  
Lasers are light sources with high energy density and good monochromaticity and directionality [4]. Since their invention, lasers have been used for many applications; in fact, lasers are a high-tech tool used to meet the challenges of sustainable agriculture [5]. For instance, lasers can be used as biostimulator devices, and studies have shown that laser irradiation can stimulate various plant organs and tissues [6, 7, 8]. The irradiation of seeds, seedlings or plants by a low-intensity laser can improve their yield and quality due to stimulation of their biochemical and physiological processes [9, 10]. In addition, lasers are biological inhibition devices, and some studies have shown that the thermal effects of lasers can damage or cause localized mortality in biological tissues [11, 12, 13]. Compared with traditional treatments [14], the use of laser irradiation for weed control has shown good results in terms of effectiveness, efficiency and environmental protection [15, 16, 17].  
Similarly, lasers can also be used in agricultural pest control. The effect of lasers for pest determination or as a pest deterrent has been investigated since the 1960s [18; 19; 20]. These studies prove that the laser-based pest control uses the laser's thermal effect to damage or kill larvae. When the laser irradiation intensity exceeds the absorption level of the epidermis, heat damages the local exoskeleton and the internal tissue under it [21]. [PERSON] et al. [22] conducted the laser irradiation experiment of drosophila and demonstrated the irradiation of mosquitos or fly pests can cause death or infertility. [PERSON] et al. [23] studied the effect of 254 nm laser irradiation on egg hatching and adult emergence of the stored-grain pest eggs. The significantly reduced hatching and adult emergence caused by laser irradiation in the experimental pests proved that irradiation is an efficacious method for pest control. [PERSON] et al. [24] used the short laser pulses to kill flying pests and studied the effect of laser pulses with different working parameters on the mortality of mosquitoes. [PERSON] et al. [25] proved that laser irradiation can kill arthropod pests, including eggs, nymphs and adults, and had a significant impact on eggs hatching, adult emergence and mortality of the tropical warehouse moth _Ephestia cutella_ ([PERSON]).  
Studies have shown that the biological effects of laser-controlled biological tissue are related to the wavelength, laser power, irradiation area, laser opening time and irradiation position [26; 27]. In this study, the controlling effect of 450 nm laser on _P. rapae_ larvae and the experimental factors of lasers (laser power, irradiation area, laser opening time and irradiation position) were studied. Furthermore, the optimal combination of working parameters was estimated. Ultimately, through verification test, the universality of its ability to prevent the _P. rapae_ at different instars attack was evaluated.