Aedes aegypti is a vector for many diseases worldwide, including malaria, dengue fever, yellow fever and Zika [1,2]. Therefore, mosquito control has become an important measure to prevent the spread of various diseases [3]. Light-activated pesticides, as photosensitive compounds, can be converted into high-energy single-linear oxygen, superoxide anion and other active substances under light, thus destroying the cell structure and metabolic process of harmful organisms [4]. The strong oxidative stress produced by these substances can cause the peroxidation of biomolecules in harmful organisms, leading to organism death. [5]. At present, a lot of research work has been done on light-activated pesticides, both domestically and internationally, including the biological activity against various mosquito fly larvae [6]. Acridines have attracted considerable interest in the field of photoactivated drug research because of their conjugated π-electron structure and aromatic nature [7]. In recent years, thiophenes, acridines and furanocoumarins have been reported to have light-activated larvicidal activity, and triple thiophene is a larvicidal agent because of its extremely significant effect on mosquito larvae [8].

9-methylacridine (AD-9-Me) is a precursor of acridine analogues, whose molecular structure contains activatable aromatic rings and methyl groups that can form excited states by photoexcitation and participate in photochemical reactions [9]. AD-9-Me has a wide range of applications, and its photophysical and chemical properties can be adjusted by chemical modification to enhance photocatalytic reaction performance [10]. Additionally, AD-9-Me can be used as a fluorescent probe in bio-imaging, analysis and detection owing to its excellent fluorescent properties, particularly in observing activities and changes in biomolecules and cells [11]. AD-9-Me is also used as a preservative to prevent corrosion and contamination of metallic materials [12]. When AD-9-Me is irradiated by ultraviolet light, some electrons in its molecule are excited to high-energy states, forming excited-state molecules with triplet states. These molecules react with surrounding oxygen molecules to form triplet oxygen, which has strong oxidation ability and can react with hydrocarbon bonds or amino groups in DNA molecules, thereby causing oxidative damage to DNA [11]. However, little research into AD-9-Me has been conducted in the agricultural field.

This study used Aedes aegypti (A. aegypti) larvae as the research object and AD-9-Me as the test agent. The difference in the toxicity of AD-9-Me to mosquito larvae under light and dark treatments was determined, and the effect of sublethal concentration of AD-9-Me under light treatment on the growth, development and motor function of A. aegypti is studied. Fluorescence observation was performed to analyse the tissue localisation of AD-9-Me in the test insect body. Further morphological, histological, cytological and molecular methods were used in exploring the mechanism of AD-9-Me's photoactivation damage to A. aegypti, laying the foundation for the development of efficient and low-toxicity agricultural photoactivation agents.