# A Laser Irradiation Method for Controlling _Pieris rapae_ Larvae
## 4 Discussion  
This research proposes a laser irradiation method for managing _P. rapae_ larvae as an alternative to chemical control. The effectiveness of controlling larvae and the influencing factors of 450 nm lasers were studied. Furthermore, the optimal combination of parameters was estimated. The results indicate the noncontact method of laser irradiation exhibits high efficiency at controlling _P. rapae_ larvae. It has been shown that many insecticides, such as 1.8% avermectin, 5% chlorobenzamide, 6% spinctoram and some plant extracts [43; 44; 45; 46; 47], have been commonly used to control _P. rapae_ larvae in recent years. Most of these insecticides exhibited a pest reduction rate of less than 80% within 3 days after treatment, and the insecticidal effectiveness decreased over time [47]. Moreover, among the 74 plant extracts tested, the most effective plant extract caused an antifeedant percentage of 96.10% after 48 h [43]. After 24 h, the laser-based method used in this research showed the same insecticidal effectiveness on larvae as traditional chemical control for 3 days and the increase in the antifeedant percentage after 48 h reached 99.27%. Thus, the laser-based method for controlling larvae exhibits the merits of avoiding the development of resistance and effectively reducing the harm of pesticide residues in the environment to human beings. At present, the frequency vibration insecticidal lamp is widely used in physical control methods [48]. The lamp uses the phototaxis of pests to lure pests and then kill them through the power grid. According to the investigation of [PERSON] et al. [49], the lamp can trap and kill 30 species of pests in 5 orders and 17 families and can trap and kill pests in main orders and families in vegetable fields. However, the lamp has the same killing ability for beneficial insects and nontarget insects in the control area, threatening the natural  
Figure 4: Antifeedant percentages (**a**) and mortality rates (**b**) (Mean \(\pm\) SE) of 1 st- to 5 th-instar _P. rapae_ larvae in optimal working parameters tests. Bars with the same letters indicate no significant difference among the tested groups within each observation time (ANOVA followed by [PERSON]’s honestly significant difference test, \(p\) > 0.05), while test between different observation times cannot be compared with each other. ecological balance [50]. On the other hand, the above methods have a certain trapping and killing effect on adults such as moths but have no effect on larvae directly endangering vegetable crops. The application of other laser technologies to control pests is mainly aimed at stored grain pests and adult pests such as flies, which cannot move by themselves and need long-term irradiation [25; 51]. However, the control method proposed in this study directly affects larvae, and the laser opening time is only 1.117 s. This approach can achieve the target killing of crop pests through a noncontact method. Moreover, the results of the study on _P. rapae_ can be used as a basis for laser control of other _Lepidoptera_ pests. Unified approaches for killing a variety of pests remain to be studied further. As revealed from the mentioned research and the experimental results of the paper, the laser irradiation method exhibits high efficiency at controlling _P. rapae_ larvae. In addition, the results here can provide support for eventually application in the field to replace or compliment insecticides and other pest management techniques. This paper also proposes a physical control method for controlling larvae by laser irradiation. In this method, machine vision is used to accurately identify and locate _P. rapae_ larvae in a field or processing plant, and a laser actuator is then used to perform a precise strike to achieve efficient and pollution-free pest mortality. Presently, [PERSON] et al. [52] and our team [53] both designed a laser pest control device based on machine vision.