Chemical Constituents of the Essential Oil Extracted from Elsholtzia densa and Their Insecticidal Activity against Tribolium castaneum and Lasioderma serricorne

Storage pests pose a great threat to global food security. Here, we found that the essential oil (EO) extracted from E. densa possesses obvious effects against the insects that threaten stored-products. In this work, we investigated the chemical constituents of the essential oil extracted from Elsholtzia densa, and their insecticidal (contact and fumigant) toxicity against Tribolium castaneum and Lasioderma serricorne. A total of 45 compounds were identified by GC-MS, accounting for 98.74% of the total EO. Meanwhile, 11 compounds were isolated from the EO, including limonene, β-caryophyllene, ρ-cymene, trans-phytol, α-terpineol, linalool, acetophenone, 1,8-cineole, ρ-cymen-7-ol, 1-O-cerotoylgly-cerol, and palmitic acid. Furthermore, acetophenone, ρ-cymen-7-ol, and 1-O-cerotoylgly-cerol were isolated for the first time from Elsholtzia spp. The results of the bioassays indicated that the EO had the property of insecticidal toxicity against T. castaneum and L. serricorne. All of the compounds showed different levels of insecticidal toxicity against the two species of insects. Among them, 2-ethyl-1H-imidazole had no insecticidal toxicity against T. castaneum, but possessed fumigant and obvious contact toxicity against L. serricorne. ρ-Cymen-7-ol had beneficial insecticidal toxicity against the two species of insects, and fumigant toxicity against L. serricorne. ρ-Cymen-7-ol (LD50 = 13.30 μg/adult), 1-octen-3-ol (LD50 = 13.52 μg/adult), and 3-octanol (LD50 = 17.45 μg/adult) showed significant contact toxicity against T. castaneum. Acetophenone (LD50 = 7.07 μg/adult) and ρ-cymen-7-ol (LD50 = 8.42 μg/adult) showed strong contact toxicity against L. serricorne. ρ-Cymene (LC50 = 10.91 mg/L air) and ρ-cymen-7-ol (LC50 = 10.47 mg/L air) showed powerful fumigant toxicity to T. castaneum. Limonene (LC50 = 5.56 mg/L air), acetophenone (LC50 = 5.47 mg/L air), and 3-octanol (LC50 = 5.05 mg/L air) showed obvious fumigant toxicity against L. serricorne. In addition, the EO and its chemical compounds possessed different levels of repellent activity. This work provides some evidence of the value of exploring these materials for insecticidal activity, for human health purposes. We suggest that the EO extracted from E. densa may have the potential to be developed as an insecticidal agent against stored product insect pests.

DELPHINIUM LEPTOCARPUM NEVSKI AND DELPHINIUM PARADOXSUN BGE AS POTENTIAL SOURCES FOR PEST CONTROL IN CEREALS AND LEGUMES

In the present study, the insecticidal activity of plant extracts from the aerial parts of Delphinium leptocarpum Nevski and Delphinium paradoxsun Bge against two major important legume insect pests, cowpea weevils (Callosobruchus maculates) and the rice weevil (Sitophilus oryzae), was studied. According to the screening results, the insecticidal toxicity of the chloroform extract of plant D. leptocarpum N. showed LC50 value of 0,70 mg / mL for adult C. maculates, 0,81 mg / mL for S. oryzae, respectively. The toxicity of the alcoholic extract of D. paradoxsun B. is LC50 0,35 mg / mL for adult C. maculates, 0,39 mg/ mL for S. oryzae, respectively. Exposure to the chloroform extract of D. leptocarpum N. at concentration of 5-10 mg / mL for 24 hours resulted in 83.0100% mortality. After 48 h exposure, the pest mortality was 100%. Under the influence of an alcoholic extract of D. paradoxsun B. at dose of 5-10 mg /mL, the mortality of pests reached 99-100%. The probable use of extracts of D. leptocarpum N. and D. paradoxsun B.as bioinsecticides is discussed here.

The Inhibition of Serine/Threonine Protein Phosphatase Type 5 Mediates Cantharidin Toxicity to Control Periplaneta americana (L.)

The American cockroach, Periplaneta americana (L.), is a notorious urban pest. It has developed insecticidal resistance to commonly used insecticides. Cantharidin (CTD) is a defensive toxin derived from blister beetles. It has been verified to have insecticidal toxicity in a range of pests. In this study, we determined the ingestion toxicity of CTD and norcantharidin (NCTD) to P. americana to test whether they had the potential to be effective against P. americana. Bioassays revealed that CTD produces toxicity against P. americana. The median lethal concentration (LC50) value of CTD was 50.92 μg/mL, while NCTD displayed nearly no toxicity against P. americana. The inhibition assays of serine/threonine protein phosphatases (PSPs) in P. americana indicated that CTD and NCTD could inhibit PSPs. The value of the half maximal inhibitory concentration (IC50) of CTD was 7.21 ± 0.94 μM, whereas that of NCTD was higher, at 31.65 ± 3.87 μM. Furthermore, the inhibition effect of CTD on the serine/threonine protein phosphatase type 5 of P. americana (PaPP5) was superior to that of NCTD. Specifically, the IC50 of CTD reached 0.39 ± 0.04 μM, while the IC50 of NCTD was 1.87 ± 0.23 μM. This study paves the way for insect-derived agents (CTD) to be applied toward controlling P. americana and contributes to the development of novel insecticides based on PP5 as a target.

Developing a Highly Stable Carlina acaulis Essential Oil Nanoemulsion for Managing Lobesia botrana

The growing interest in the development of green pest management strategies is leading to the exploitation of essential oils (EOs) as promising botanical pesticides. In this respect, nanotechnology could efficiently support the use of EOs through their encapsulation into stable nanoformulations, such as nanoemulsions (NEs), to improve their stability and efficacy. This technology assures the improvement of the chemical stability, hydrophilicity, and environmental persistence of EOs, giving an added value for the fabrication of natural insecticides effective against a wide spectrum of insect vectors and pests of public and agronomical importance. Carlina acaulis (Asteraceae) root EO has been recently proposed as a promising ingredient of a new generation of botanical insecticides. In the present study, a highly stable C. acaulis-based NE was developed. Interestingly, such a nanosystem was able to encapsulate 6% (w/w) of C. acaulis EO, showing a mean diameter of around 140 nm and a SOR (surfactant-to-oil ratio) of 0.6. Its stability was evaluated in a storage period of six months and corroborated by an accelerated stability study. Therefore, the C. acaulis EO and C. acaulis-based NE were evaluated for their toxicity against 1st instar larvae of the European grapevine moth (EGVM), Lobesia botrana (Denis & Schiffermüller, 1775) (Lepidoptera: Tortricidae), a major vineyard pest. The chemical composition of C. acaulis EO was investigated by gas chromatography–mass spectrometry (GC–MS) revealing carlina oxide, a polyacetylene, as the main constituent. In toxicity assays, both the C. acaulis EO and the C. acaulis-based NE were highly toxic to L. botrana larvae, with LC50 values of 7.299 and 9.044 µL/mL for C. acaulis EO and NE, respectively. The C. acaulis-based NE represents a promising option to develop highly stable botanical insecticides for pest management. To date, this study represents the first evidence about the insecticidal toxicity of EOs and EO-based NEs against this major grapevine pest.

Dört Farklı Bitki Ekstraktının Patates Güvesi [(Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)] Yumurta ve Larvasına Karşı Toksik Etki Çalışması

Two different thyme species (Thymus vulgaris L. and Origanum majorana L.), sage (Salvia officinalis L.) and lavender (Lavandula officinalis L.) extracts were tested against pre-adult stage of Potato tuber moth-PTM [(Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)], which is an important quarantine pest. Each plant extracts prepared with ethanol were applied to larvae and eggs in three different concentrations 3%, 5 and 10 ml/L. In the egg treatments at the highest concentration (10% ml/L), inhibition rate was observed in Lavander and T. vulgaris 73.7%, in O. majorana 67.5% and in sage 66.2%, respectively. Results indicated that the mean number of hatching eggs were highly decreased as concentration increased, the highest decreased was observed with treated 10% concentration. of lavender and T. vulgaris. Observation were for 7 days. In the insecticidal toxicity study of against the larval stage, mortality were determined at the highest concentration (10% ml/L) in O. majorana 91.2%, Lavander 90%, T. vulgaris 87%, and Sage 83.7% at the end of 7th day. It was also determined that the larval mortality rate was higher with the increasing of extracts of 4 different plant depending on time. As a result, in this study, ovicidal toxicity of plant extracts was recorded against to on egg stage and it was that impact of insecticidal against to on larval stage also.