Insecticidal Activity of Lamiaceae Plant Essential Oils and Their Constituents Against Blattella germanica L. Adult

Subcellular-Level Mitochondrial Energy Metabolism Response in the Fat Body of the German Cockroach Fed Abamectin

Mitochondria are the leading organelle for energy metabolism. The toxic effects of environmental toxicants on mitochondrial morphology, energy metabolism, and their determination of cell fate have already been broadly studied. However, minimal research exists on effects of environmental toxicants such as pesticides on mitochondrial energy metabolism at in vitro subcellular level, particularly from an omics perspectives (e.g., metabolomics). Here, German cockroach (Blattella germanica) was fed diets with (0.01 and 0.001 mg/mL) and without abamectin, and highly purified fat body mitochondria were isolated. Swelling measurement confirmed abnormal mitochondrial swelling caused by abamectin stress. The activity of two key mitochondrial energy metabolism-related enzymes, namely succinic dehydrogenase and isocitrate dehydrogenase, was significantly affected. The metabolomic responses of the isolated mitochondria to abamectin were analyzed via untargeted liquid chromatography/mass spectrometry metabolomics technology. Fifty-two differential metabolites (DMs) were identified in the mitochondria between the 0.001 mg/mL abamectin-fed and the control groups. Many of these DMs were significantly enriched in pathways involved in ATP production and energy consumption (e.g., oxidative phosphorylation, TCA cycle, and pentose phosphate pathway). Nineteen of the DMs were typically related to energy metabolism. This study is valuable for further understanding mitochondrial toxicology under environmental toxicants, particularly its subcellular level.

Development of cellulose nanocrystal-stabilized Pickering emulsions of massoia and nutmeg essential oils for the control of Aedes albopictus

We investigated the larvicidal potential of 10 plant essential oils (EOs) against the Asian tiger mosquito Aedes albopictus. Among the EOs, larvicidal activity against Ae. albopictus was strongest in those derived from massoia (Massoia aromatica) and nutmeg (Myristica fragrans). Larvicidal activities of massoia and nutmeg EOs against Ae. albopictus were 95.0% and 85.0% at 50 μg/mL, respectively. A total of 4 and 14 compounds were identified from massoia and nutmeg, respectively, and two massoia lactones, C10 and C12, were isolated from massoia EO. Among the identified compounds, benzyl salicylate, terpinolene, C12 massoia lactone, sabinene, benzyl benzoate, methyl eugenol, and C10 massoia lactone exhibited the strong larvicidal activity. Cellulose nanocrystal (CNC)-stabilized Pickering emulsions of massoia and nutmeg EOs were developed to overcome the insolubility of EOs in water. CNC/massoia and CNC/nutmeg emulsions were stable for at least 10 days, and larvicidal activities of CNC/massoia PE and CNC/nutmeg were higher than those of crude massoia and nutmeg EOs. This study presents a CNC-stabilized PE, a suitable formulation for EOs, as a potential larvicide against Ae. albopictus.

Topical Toxicity Profiles of Some Aliphatic and Aromatic Essential Oil Components Against Insecticide-Susceptible and Resistant Strains of German Cockroach (Blattodea: Ectobiidae)

Toxicity profiles of four aliphatic (α-pinene, cyclononanone, limonene, nerolidol), four aromatic (β-thujaplicin, carvacrol, eugenol, tropolone) essential oil components (EOCs), and permethrin were investigated against three strains of German cockroach, Blattella germanica (L.). The strains include a susceptible strain (S), and two multi-resistant strains - strains D and E. Also, a synergism bioassay, using piperonyl butoxide (PBO) was conducted. The most toxic EOCs were aromatic EOCs carvacrol, eugenol, and tropolone, followed by aliphatic EOC limonene; all had LD50 values of <0.7 mg/µl. Four of the EOCs were equally toxic against all the strains, with carvacrol being the most toxic, followed by eugenol, tropolone, and α-pinene. The other four EOCs were more toxic against strain S than against the two resistant strains. Permethrin was significantly more toxic to strain S (LD50 = 0.056 µg/µl) compared with the resistant strains (D = 2.138 µg/µl, E = 1.730 µg/µl). Toxicity of aliphatic EOCs correlated positively with their molecular weight against strain E only, whereas both molecular weight and vapor pressure of aromatic EOCs correlated significantly with toxicity in all strains. Strain D exhibited the greatest resistance (RR of 6.7) to EOCs, and synergism to the aliphatic EOC cyclononanone. Clear synergism with PBO was observed in permethrin against resistant strains, but not in all of the EOCs, suggesting multiple resistance mechanisms in the resistant cockroaches. These findings give insight on the potential of EOCs to be incorporated as parts of an IPM approach to managing insecticide resistant German cockroaches.

Insecticidal application of essential oils loaded polymeric nanoparticles to control German cockroach: Design, characterization and lethal/sublethal effects

Essential oils (EO) from peppermint, palmarosa, geranium, lavender and rosemary were tested against the German cockroach, Blatella germanica L. (Blattaria: Blatellidae). Peppermint and palmarosa oils were the most effective and were included in a polyethylene glycol 6000 matrix to obtain EO loaded polymeric nanoparticles (EOPN). The physicochemical analyses indicated that, at 7 days postformulation, peppermint EOPN had sizes of 380 nm, the loading efficiency (LE) was 72.25% and the polydispersity index (PDI) was >0.4 (polydisperse sample). Palmarosa EOPN had sizes of 191 nm; LE was 89.75% and PDI was <0.25 (monodisperse sample). Peppermint and palmarosa EOPN enhanced the lethal and sublethal effects of the EO on B. germanica. These results suggest that the newly developed nanoinsecticides could be successfully used to control German cockroach.