The development of “green” alternatives to chemical pesticides could play a crucial role in integrated pest management (IPM). Their use is considered either as a substitution for or in addition to hazardous synthetic products. We analysed the influence of three concentrations of tansy (Tanacetum vulgare L.) essential oil (EO), previously characterised by GC-MS, on the survival and moulting of the 2nd instar and the nutritional indices of the 4th instar gypsy moth (Lymantria dispar L.) larvae. In a residual contact toxicity assessment, the exposure to tansy EO caused low mortality (< 10%) while larval development was significantly slowed down, i.e., the percentage of larvae that moulted into the 3rd instar was reduced. On the other hand, when tansy EO was incorporated into the diet (digestive toxicity assay), high mortality and a lack of moulting after 120 h of eating were recorded for the highest applied concentration of EO. During 48 h of feeding on EO-supplemented food at concentrations of 0.5 and 1% (v/v), the relative growth rate (RGR) of the 4th instar larvae significantly decreased, which can be explained by a significant reduction of the relative consumption rate (RCR) and significantly or marginally significantly lower efficiency of conversion of ingested food into insect biomass (ECI). Although the RCR was also reduced with the lowest applied EO concentration (0.1%), the ECI was not affected which meant the RGR was as high as it was for the control larvae. ECI changes, when two higher EO concentrations were applied, were due to a reduction in the efficiency of conversion of digested food into biomass (ECD), while approximate digestibility was unaffected by the presence of EO in the food. Our results on the significant negative effects of tansy EO on gypsy moth larval survival, development time, and nutritional physiology suggest that it could be considered in future designs for botanical insecticides for gypsy moth control.

Itol A, an isoryanodane diterpene derived from Itoa orientalis Hemsl. (Flacourtiaceae), is a potential plant-based insecticide. However, the effect of itol A on the tobacco cutworm [Spodoptera litura (Fab.) (Lepidoptera: Noctuidae)], an important and widely distributed insect pest, remains unclear. In this study, the toxicity and inhibitory potency of itol A on S. litura were evaluated. The results indicated that itol A exhibited larvicidal activity against the third instar larvae in a concentration-dependent manner (LC₅₀ 875.48 mg/L at 96 h). Antifeedant activity also was observed, and the 24-h AFC₅₀ values were 562.05 and 81.47 mg/L in the no-choice and choice experiments, respectively. The insect growth was inhibited after treatment of itol A, as reflected by long developmental periods, low-quality pupae, and various abnormalities. Itol A exerted ovicidal effect on S. litura, with an estimated LC₅₀ of 759.30 mg/L. Itol A deterred oviposition in the choice experiment (ODI₅₀ 909.60 mg/L). Besides, the activities of α-amylase, general protease, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were inhibited after itol A treatment over time compared to controls, which may be a relevant mechanism underlying the toxicity of itol A toward S. litura. However, the activities of lipase, carboxylesterase (CarE), glutathione S-transferase (GST), and cytochrome P450 monooxygenase (P450) were increased. Taken together, these results suggest that itol A could be a good botanical pesticide to reduce the population of S. litura in integrated pest management programs.

The knockdown and adulticidal activities of individual Cymbopogon citratus and Eucalyptus globulus essential oils (EOs) and their combinations were evaluated against three medical insect pests (Aedes aegypti, Aedes albopictus, and Musca domestica) using a WHO susceptibility test. The knockdown and adulticidal activities against the three medical insect pests of combinations of C. citratus and E. globulus EOs were higher than those of individual EOs alone. Combinations of 7.5% C. citratus + 7.5% E. globulus EOs and 10% C. citratus + 10% E. globulus EOs exhibited the highest efficacy against females of the three species with 100% knockdown and mortality rates at 1 and 24 h after exposure, respectively. Their adulticidal activities were equivalent to that of 10% w/v cypermethrin. In contrast, 70% v/v ethyl alcohol negative control was not effective at all. The combinations of EOs showed a synergistic effect, i.e., their adulticidal activity was improved by 0.2 to 100%, with increased knockdown and mortality rates, compared to individual EOs. The highest synergistic effect on effective knockdown and adulticidal activities against females of the three species was achieved by a combination of 2.5% C. citratus + 2.5% E. globulus EOs, with 36.6 to 100% knockdown rate increase and 33.5 to 98.9% mortality rate increase. This study demonstrates that all tested combinations of C. citratus and E. globulus EOs were effective adulticidal agents against females of Ae. aegypti, Ae. albopictus, and M. domestica and have a high potential for development into a botanical insecticide for controlling populations of Aedes mosquitoes and houseflies.