Hematophagous mosquitoes, as medically relevant insects, transmit many micro- and macro-parasitic pathogens to humans, causing diseases such as malaria, dengue fever, yellow fever, Zika-virus fever, chikungunya, and filariasis (Rocklöv and Dubrow, 2020; Kilpatrick and Randolph, 2012). Malaria imposes a remarkable cost on the government and community; it has been estimated that about 1.5 billion people were globally infected with malaria parasites, and almost 7.6 million died from 2000 to 2019 (Saberi et al., 2022). In 2021, 247 million cases and 619,000 deaths were reported in 84 malaria-endemic countries. Nearly 96% of all malaria-related deaths worldwide occurred in just 29 countries. However, in 2022, a significant milestone was achieved as countries and partners raised an unprecedented amount of US$ 15.9 billion for malaria control through the largest replenishment in the history of the Global Fund (WHO, 2023).

Anopheline mosquitoes, of which there are >400 Anopheles Meigen, 1818 (Diptera: Culicidae) species (Azari-Hamidian et al., 2019), transmit the protozoan Plasmodium leading to malaria (Gilles and Warrell, 1996). Some 40 species can vector human malaria worldwide (Azari-Hamidian et al., 2019). Anopheles stephensi Liston is known as the primary vector of malaria (Hoosh-Deghati et al., 2017; Azari-Hamidian et al., 2019) in the Eastern Mediterranean Region (Enayati et al., 2020), which is currently expanding its range and distribution into the African continent necessitating a strong signal to implement further research on this mosquito.

Though malaria vector control causes major reductions in parasite transmission, applying chemical insecticides against mosquitoes has led to the deterioration of environmental balance and destructive effects on humans and animals (Tudi et al., 2021). These chemicals also endanger non-target organisms, which could partially lead to elimination of useful insects in the environment. Besides, repetitive and irregular use of toxic chemicals has generated insect resistance (Sánchez-Bayo, 2021; Pathak et al., 2022). New methods of mosquito control are thus currently under way for subsequent implementation. These botanical insecticides are promising since they are cheap, non-toxic on non-target organisms, compatible with the environment, and readily biodegradable (Werdin González et al., 2017). Natural insecticides may possess mosquito larvicidal and/or imagicidal (adult-killing) molecules. In addition, they use different mechanisms and modes of action, which could alleviate mosquito resistance (Sanei-Dehkordi et al., 2021; Pavela et al., 2019). The insecticidal characteristics of various plant essences and oils against mosquito larvae have been investigated (Osanloo et al., 2022; Sanei-Dehkordi et al., 2022c).

Essential oil (EO) treatment of mosquitoes is an important part of future mitigation strategies. Herbal EOs have been introduced as effective alternative sources of repellents, larvicides, and imagicides against some insects (Radwan et al., 2022; Moemenbellah-Fard et al., 2021). Furthermore, botanical insecticides usually act specifically and are safe for humans. Plant EOs are volatile odorant organic compounds (VOCs) with flavor/fragrance and immediately sublimating or evaporating constituents from different parts such as seed, stem, bark, leaf, flower, and rhizome (Mun and Townley, 2021; Noorpisheh Ghadimi et al., 2020). Due to their high volatility, EOs are enclosed in nanostructured shells like nanoliposomes (Mozafari, 2010; Lammari et al., 2021). In addition, liposomes could increase the EOs' solubility and stability and protect them from evaporation and oxidation (Zarenezhad et al., 2022). For instance, by loading eugenol into nanoliposomes, its larvicidal efficacy was substantially improved; its inhibitory concentration at 50% (IC50) value decreased from 67.6 to 5.4 μg/mL (Sanei-Dehkordi et al., 2022b). In addition, nanoliposomes containing EO have been widely used in all medicinal fields. Nanoliposomes containing Citrus aurantium EO with a particle size of 52 nm showed a lethal concentration at 50% (LC50) value of 6.63 μg/mL against An. stephensi larvae (Sanei-Dehkordi et al., 2022c), while those of Zataria multiflora exhibited an LC50 value of 10.88 μg/mL against the same mosquito larvae (Sanei-Dehkordi et al., 2022a).

Trachyspermum ammi (L) Sprague (known as Ajwain or Ajowan) is an annual herbal member of the Apiaceae family (Ardestani et al., 2020; Torabi-Pour et al., 2017). Previous phytochemical analyses have demonstrated that T. ammi EO (TAEO) has different compounds such as carbohydrates, saponins, proteins, volatile or essential oils (e.g., thymol, γ-terpinene, para-cymene, etc.), and various minerals like phosphorus, calcium, and iron (Chahal et al., 2017). TAEO exhibits anti-oxidant, anti-inflammatory, anti-microbial, gastro-protective, immunomodulatory, and bronchodilator activities (Vitali et al., 2016; Qamar et al., 2020; Escobar et al., 2020). To the best of the authors’ knowledge, this is the first survey on the efficacy of nanoliposomes of TAEO against malaria mosquito larvae. The main aim of this study was to investigate the larvicidal effect of nanoliposomes containing TAEO (TAEO-NL) against the main malaria vector, An. stephensi Liston.