Characterization of P. oleracea, R. sativus, and R. officinalis Oil Nano-Emulsions

The prepared nano-emulsion formulations which contain 10% (ml/ml) of P. oleracea, R. sativus, and R. officinalis were characterized in terms of droplet size, polydispersity index (PDI), zeta potential, morphological structure, and thermodynamic characterization (Table 4). The droplet size distribution and morphological structure of purslane, rosemary, and radish oil nano-emulsions are shown in Figs. 1 and 2. In our study, the average size of the nano-emulsions was found to be less than 200 nm; the particle sizes for purslane radish and rosemary are 26.67 nm, 134.9 nm, and 97.36 nm. The obtained values in this study of PDI are less than 0.3; the PDI of purslane oil is 0.186, 0.190 for radish oil, and 0.202 for rosemary. Zeta potential which characterizes the surface charge of the nano-emulsion particles is an important factor for nano-emulsion stability. Zeta potentials of purslane, radish, and rosemary nano-emulsions are − 0.69 mV, − 29.9, mV, and − 18.00 mV, respectively (Table 4). The TEM images (Fig. 2) investigated the spherical appearance of synthesized o/w nano-emulsion and showed droplet mean size in the range of 200 nm.

The stability of nano-emulsion formulations is an important character that indicates the shelf-life of the formulations. The prepared nano-emulsions passed the thermodynamic tests (freeze–thaw cycle, centrifugation, and heating–cooling cycle). The nano-emulsions showed stable formulation without any sign of instability such as phase separation sedimentation or creaming. The nano-formulations were physically stable up to 3 months from the preparation. The viscosity of prepared nano-emulsions is 24.7 mPas for purslane, 26 mPas for radish, and 6.5 mPas for rosemary (Table 4).

Toxicity Effects of Oils and Their Nano-Emulsions

The pesticidal efficacy of purslane, radish, and rosemary oil–based nano-emulsions was compared to that of the pure oil against A. gossypii, S. littoralis, and T. urticae in this study. It is clear from data presented in Tables 5 and 6 that all formulation forms caused different mortality levels against the selected pests after 24 h from exposure.

The results showed that the tested oils have positive toxic effects, and purslane oil exhibited the highest insecticidal activity against A. gossypii with LC 50 = 85.02 mg /L followed by radish and rosemary with LC 50 = 555.42 and 869.64 mg /L, respectively. However, rosemary and purslane oil nano-emulsion record the same greatest impact on A. gossypii with LC 50 = 72.45 and 72.74 mg /L, respectively, followed in descending order with radish oil nano-emulsion with LC 50 = 453.91 mg /L. Furthermore, the acaricidal activity of the tested oils and their nano-emulsion against T. urticae is presented in Table 5. According to the LC 50 values, purslane oil is most active than radish and rosemary oil, with LC 50 values = (291.05, 235.86), (359.95, 263.54) and (337.46, 240.98) mg/L, for bulk and nano-emulsion oil, respectively. These results indicate that the tested oil nano-emulsions have efficiency and may be used as insecticide and acaricide agents.

PDI poly disparity index

√—passed the test

aLC median lethal concentration (concentration which caused 50% mortality of the tested adults)

50 bSlope of the concentration—mortality regression line ±standard error

cLC concentration causing 90% death for the tested adults

90 dIntercept of the regression line ±S.E

eChi-square value

The insecticidal effects of the tested oils and their nano-emulsions using the residual bioassay method on 4th instar larvae of S. littoralis are shown as LD 50 values in Table 6. All oils caused mortality against S. littoralis compared with the control, the result indicating that among the tested oils, purslane oil (nano and bulk) had a high toxic effect against S. littoralis after 24 h (LD 50 = 55.35 ppm and 96.1 ppm), followed by rosemary (nano and bulk) with LD 50 = 120 ppm and 113 ppm, respectively. Conversely, radish oil (nano and bulk) was less effective on S. littoralis with LD 50 = 123.06 and 140.89 ppm (nano and bulk).