Broccoli (Brassica oleracea L. var. italica) contains high levels of fiber, minerals, and antioxidants, which are beneficial for health(Handayani & Ayustaningwarno, 2014). According to Statistic Indonesia(Statistik, 2023), cabbage and broccoli production in West Sumatra decreased by 17.62%, from 211,711 tons in 2020 to 174,387 tons in 2021. One of the contributing factors to this decline is the incidence of plant-disrupting organisms, including of plant pests, pathogens, and weeds. Pests and diseases are major causes of yield instability in cabbage and broccoli crops. Among the most damaging insect pests affecting these crops are cabbage head caterpillar (Crocidolomia pavonana Fab.) and the diamondback moth (Plutella xylostella Linn.), both of which are key pests of Brassicaceae crops(Jamtsho et al., 2021).

Farmers continue to rely on synthetic insecticides to control C. pavonana and P. xylostella, primarily due to their practicality, cost-efficiency, and quick action in reducing pest populations(Indiati & Marwoto, 2017). However, if used unwisely, synthetic insecticides can have adverse effects such as pest resistance, pest resurgence, and mortality of non-target organisms(Indiati & Marwoto, 2017). Insecticides, including carbamate and organophosphates, are extensively utilized in agriculture and have the potential to lethally affect various non-target organisms, such as earthworms, natural enemies (predators and parasitoids), and other ecologically significant species. Research indicates that the insecticides carbosulfan, carbofuran, and BPMC result in the mortality of the earthworm Eisenia fetida, with mortality rates ranging from 66% to 76% at elevated concentrations (300 mg/kg)(Kinasih et al., 2014). Therefore, botanical insecticides are considered a promising alternative, as they offer a more environmentally friendly approach and help mitigate the negative consequences associated with synthetic insecticide use.

Botanical insecticides offer several advantages, such as biodegradability, environmental friendliness, and a lower risk of inducing pest resistance(Yusuf, 2012). Several plant species possess the potential to be developed into effective insecticides. According to previous reports, spiked pepper (Piper aduncum L.) contains secondary metabolites such as dillapiole, alkaloids, flavonoids, phenolics, triterpenoids, steroids, saponins, and coumarins. P. aduncum acts as a contact poison, a stomach poison, and an antifeedant(Arneti, 2012). The secondary metabolites produced by P. aduncum are known to possess insecticidal activity(Safrida et al., 2020). Spiked pepper has been utilized as a plant-based insecticide in conventional formulations such as emulsifiable concentrate (EC) and wettable powder (WP). Botanical insecticides are generally considered environmentally friendly because they are biodegradable and tend to degrade rapidly in the environment after application. However, in EC and WP formulations still present several limitations, including phytotoxicity, the presence of residues on plant surfaces after application, and reduced adhesion or persistence on foliage(Lina, 2014). To overcome these limitations, nanoemulsion formulations have been developed to create more effective botanical insecticidal products.

In nanoemulsion systems, two phases are involved: an organic phase and an aqueous phase. The organic phase contains plant-derived active compounds dissolved in a suitable solvent, while the aqueous phase consists of water and emulsifying agents to stabilize the emulsion. These two phases are mixed using a spontaneous emulsification technique to produce stable nanoemulsion(Lina et al., 2021). In addition to P. aduncum, citronella (Cymbopogon nardus L.) is also a potential source of plant-based insecticides. The distillation of citronella grass produces two types of liquid fractions: the essential oil itself and a by-product known as hydrosol. In this study, citronella hydrosol was used as the aqueous phase in the nanoemulsion formulation because it is environmentally friendly, readily biodegradable, and may enhance insecticidal activity compared with formulations using plain water. Hydrosol is a water-based distillation product that contains small amounts of active compounds originating from citronella essential oil, such as citronellal, citronellol, and geraniol(Saidi et al., 2021). Although present in low concentrations, these compounds exhibit biological activity, including repellent and antifeedant effects against insect pests(Lina et al., 2021). Therefore, the use of hydrosol not only serves as a carrier in the aqueous phase but also contributes additional bioactive compounds to the nanoemulsion system.

Plant-based insecticides, particularly those developed using nanotechnology, must be formulated in a stable form to ensure their efficacy. Nanoemulsion technology enables the reduction of particle size, thereby enhancing the efficiency and effectiveness of the active ingredients(Noveriza et al., 2017). Nanoemulsion formulations have been developed to improve the performance of botanical insecticides compared with earlier and commonly used formulations like EC and WP. These nanoparticle-based formulations offer several advantages, including enhanced penetration into leaf tissues, extended shelf life, resistance to sedimentation, low volatility, and improved physicochemical stability(Shakeel et al., 2008). A nanoemulsion formulation of P. aduncum extract has been shown to cause significant mortality in C. pavonana larvae, with an LC₉₅ value of 1.02%(Erlina et al., 2020). Furthermore, Lina et al. (2023a)(Lina et al., 2023) reported that nanoemulsion formulations of P. aduncum showed high larval mortality against Spodoptera frugiperda Smith. Recent studies have demonstrated that nanoemulsion-based botanical insecticides enhance the stability and bioactivity of active compounds, leading to increased larval mortality and physiological disruption in insect pests, including S. frugiperda (Campos et al. 2020; de Oliveira et el.2021).

Prior to commercialization, botanical insecticides must undergo thorough testing. Efficacy testing is a critical step in evaluating the performance of a pesticide product intended for commercial use(Fitriasari et al., 2009). This study aimed to evaluate the effectiveness of a nanoemulsion formulation containing P. aduncum extract and C. nardus hydrosol in controlling C. pavonana and P. xylostella on broccoli crops in Alahan Panjang.

In general, field observations of C. pavonana and P. xylostella larval populations, showed that untreated larval populations (control) were consistently higher than those subjected to insecticide treatments. Statistical analysis revealed that the INN, Bt, and IS treatments resulted significantly lower populations compared to the control group from 49 to 70 DAP for C. pavonana, and from 28 DAP to 70 DAP for P. xylostella.

Throughout the study, the larval populations of both pest species fluctuated significantly. Highest population occurred at 49 DAP, which aligns with findings by Kumarawati et al. (2013), who reported that the highest abundance of C. pavonana and P. xylostella larval populations on broccoli typically occurs between seven to eight weeks post-planting. Abiotic factors, particularly rainfall, influence these insect population dynamics(Murtiningsih et al., 2023). Low rainfall and intermittent drought periods when the plants were 42 - 56 DAP likely facilitated the increase in larval populations of C. pavonana and P. xylostella. Conversely, high rainfall intensity during the eighth week contributed to a decline in both pest populations by 63 DAP. Furthermore, larval abundance in the field is positively correlated with food availability, indicating that areas with more food sources tend to support higher larval populations (Kumarawati et al. 2013). At 49 DAP, broccoli plants experience the increase in leaf number. This vegetative growth increases in leaf number correlates with a heightened susceptibility to pest attacks, resulting in a rise in the populations of C. pavonana and P. xylostella during this observation period. Akter et al. (2025)(Akter et al., 2025) reported that leaf number in broccoli increases progressively during the vegetative stage, with observations commonly conducted up to around 49 days after planting (DAP).

The suppression of larval populations of C. pavonana and P. xylostella across treatments can be attributed to the specific active compounds in each formulation (Kumarawati et al. 2013). Dillapiole, a major active compound in P. aduncum, can inhibit the activity of the cytochrome P450 detoxification enzyme, which plays a role in reducing the toxicity of toxic compounds or metabolites in the larval body(Bernard et al., 1995). Previous studies have demonstrated that spiked piper extracts can cause 100% mortality in C. pavonana(Syahroni & Prijono, 2013) and 98 % mortality in P. xylostella(Lina et al., 2018). Although, the major bioactive compounds of C. nardus, such as citronellal and geraniol, are primarily present in the essential oil fraction. However, small amounts of these compounds can be carried over into hydrosol during the distillations. These carried-over compounds likely contribute to the overall insecticidal activity of the formulation by disrupting cellular metabolism and respiratory processes in insect(Araújo et al., 2023). Therefore, the combined antifeedant and toxicological effects of P. aduncum extract and C. nardus hydrosol mixture can also cause a decline in the larval populations of C. pavonana and P. xylostella(Erlina et al., 2020).

The biological insecticide B. thuringiensis (Bt) contains δ-endotoxin crystals that are lethal and can reduce the populations of C. pavonana and P. xylostella. The toxin bind to specific receptors on midgut epithelial cell, leading to pore formation, cell lysis, and gut paralysis. According to Hariyani et al. (2014)(Hariyani et al., 2014), B. thuringiensis formulations can suppress the larval populations of C. pavonana and P. xylostella by > 45%. The disadvantages of the insecticide B. thuringiensis are its sensitivity to ultraviolet light and ease of washing; therefore, its active ingredients do not last long in the field(Bahagiawati, 2002). In contrast, the synthetic insecticides with the active ingredient cypermethrin (IS) are known to have high acute toxicity and persistence, and can rapidly kill C. pavonana and P. xylostella larvae, thereby reducing pest infestation. Cypermethrin is a synthetic pyrethroid insecticide that acts on the insect nervous system by modifying the gating kinetics of voltage-gated sodium channels, resulting in prolonged depolarization, repetitive nerve firing, paralysis, and ultimately insect death(Field et al., 2017).

Application of INN, Bt and suppressed the attack of C. pavonana and P. xylostella. The results showed that the percentage of plants infested with C. pavonana and P. xylostella the same time, and broccoli plants were treated with a lower insecticide than those without insecticide treatment. The percentage of infested plants is closely related to the number of C. pavonana and P. xylostella larval populations; the higher the number of larvae, the higher the percentage of infested plants will increase(Hasnah, 2009). The percentage of infested plants increased significantly at 42 DAP and peaked at 70 DAP because of the high C. pavonana and P. xylostella populations. This aligns with Kumarawati et al. (2013), who stated that the highest percentage of plants infested with C. pavonana and P. xylostella larvae occurred in the tenth week after planting.

Based on the efficacy standard, it was found that the plant-based insecticide formulation of a nanoemulsion mixed with P. aduncum extract and C. nardus hydrosol was less effective in controlling C. pavonana and P. xylostella because it had an effectiveness percentage below 70% for five times in eight observations. The ineffectiveness of botanical insecticides is caused by the active ingredients contained in the insecticide, which cannot last long during field application because they are quickly degraded by sunlight and easily washed by rain. According to Badan Meteorologi, Klimatologi dan Geofisika (BMKG) data, the Gumanti Valley experienced rainfall amounts of 513 mm, 344 mm, and 463 mm during the planting period from July to October 2023. This indicates that these months fall into the category of wet months with significant rainfall. Therefore, the application of natural insecticides should be more frequent to increase the effectiveness of the active ingredient(Kardinan & Suriati, 2012)

The efficacy evaluation of a botanical insecticide nanoemulsion formulation of P. aduncum extract and C. nardus hydrosol demonstrated comparable activity to B. thuringiensis insecticide, although its control of C. pavonana and P. xylostella on broccoli plant was still lower than that of synthetic insecticides.