Contact Toxicity and Repellent Effects of Essential Oils from Toddalia asiatica against Two Stored-Product Insects.

Insect infestations continually endanger stored goods, underscoring the significance of discovering eco-friendly insecticides for pest management. Essential oils (EOs) from different parts of Toddalia asiatica (leaf, fruit and branch) were extracted by hydrodistillation and analyzed by GC-MS. Carvene, p-cymene and muurolene are the principal compounds of T. asiatica leaf (TAL), T. asiatica fruit (TAF) and T. asiatica branch (TAB) EO respectively. Our work aimed to assess the contact toxicity and repellent effects of EOs on two storage pests, Tribolium castaneum and Lasioderma serricorne. All tested EOs exhibited obvious contact toxicity, especially, TAL EO against T. castaneum (33.48 µg/adult) and TAF EO against L. serricorne (16.42 µg/adult). Repellency tests revealed that TAL and TAF EOs, at a concentration of 78.63 nL/cm2, achieved nearing 100% efficiency against T. castaneum. These results suggest that EOs of T. asiatica could be used as effective botanical insecticides for managing stored-product insects.

Chemical Composition, Toxicity, and Repellency of Essential Oils from Three Hedychium Species Against Stored-Product Insects.

Stored products are constantly infested by insects, so finding eco-friendly bioinsecticides for insect management is important. The work aimed to assess the insecticidal and repellent activity of essential oil (EO) from Hedychium glabrum S. Q. Tong, Hedychium coronarium Koen., and Hedychium yunnanense Gagnep. against Tribolium castaneum, Lasioderma serricorne, and Liposcelis bostrychophila. Results showed that 88 chemical components were identified in the extracted Hedychium EOs, indicating that they exhibited diversity in components. According to principal component analysis (PCA), the composition of the EO from the H. yunnanense stem and leaf (EOHYSL) was significantly different from other EOs due to the different organs and species. The biological activity also varied continuously with plant species and organs. Only the EO of H. yunnanense (EOHY) showed strong fumigant toxicity. While in the contact tests, EOHGR showed the strongest toxicity effect on L. bostrychophila, with a LC50 value of 71.76 µg/cm2, which was closest to the positive control (Pyrethrin). All EOs had remarkable repellent activities against the three target insects, and repellency increased with concentration. According to the results of the comprehensive score, EOHY had the highest potential, which ranged from 0.7999 to 0.8689. Thus, Hedychium EOs possess potential biorational traits to be biological insecticides.

Chemical Composition and Insecticidal Activities of Blumea balsamifera (Sambong) Essential Oil Against Three Stored Product Insects.

Blumea balsamifera (L.) DC. (Asteraceae), also known as sambong, is a perennial herb used in China for medicinal purposes. The essential oil (EO) of B. balsamifera was extracted by hydrodistillation. Thirty chemical components of the EO were analyzed by gas chromatography-mass spectrometry (GC-MS) and GC, accounting for 88.0% (w/w) of the total oil. The EO of B. balsamifera was mainly composed of monoterpenes and sesquiterpenes, in which borneol (23.3%), ß-caryophyllene (20.9%) and camphor (11.8%) were the major components. The insecticidal activities of the EO and its three main compounds against Tribolium castaneum, Lasioderma serricorne and Sitophilus oryzae were evaluated. The results of bioassays displayed that the EO of B. balsamifera did not have fumigant toxicity to the three target insects, but exhibited significant contact activity against L. serricorne (LD50 = 12.4 µg/adult) and S. oryzae (LD50 = 44.4 µg/adult). Meanwhile, the EO showed a notable repellent effect on T. castaneum at all testing concentrations and a general repellent effect on S. oryzae at high concentrations (78.63 nL/cm2). ß-Caryophyllene showed the best performance in the contact toxicity bioassays against the three insects. The results indicated that B. balsamifera has the potential to be used as a source of botanical insecticides for the control of stored-product insects.

Assessment of Contact Toxicity and Repellent Effects of Essential Oils from Piper Plants Piper yunnanense and Piper boehmeriifolium against Three Stored-Product Insects.

Storage is a crucial part during grain production for the massive spoilage caused by stored product insects. Essential oils (EOs) of plant origin have been highly recommended to combating insects which are biodegradable and safe mode of action. Hence, to make the fullest use of natural resources, essential oils of different parts from Piper yunnanense (the whole part, PYW; fruits, PYF; leaves, PYL) and Piper boehmeriifolium (leaves, PBL) were extracted by steam distillation method in the present study. Gas chromatography-mass spectrometry (GC-MS) characterization revealed bicyclogermacrene (PYW), γ-muurolene (PYF), δ-cadinene (PYL) and methyl 4,7,10,13,16,19-docosahexaenoate (PBL) as the principal compound of each essential oil. Sesquiterpene hydrocarbons were also recognized as the richest class accounting for 56.3 %-94.9 % of the total oil. Three storage pests, Tribolium castaneum, Lasioderma serricorne and Liposceis bostrychophila, were exposed to different concentrations of EOs to determine their insecticidal effects. All tested samples performed modest contact toxicity in contrast to a bioactive ingredient pyrethrin, among which the most substantial effects were observed in PYF EOs against T. castaneum (35.84 µg/adult), PBL EOs against L. serricorne (15.76 µg/adult) and PYW EOs against L. bostrychophila (57.70 µg/cm2 ). In terms of repellency tests, essential oils of PYF at 78.63 nL/cm2 demonstrated to have a remarkable repellence against T. castaneum at 2h and 4h post-exposure. The investigations indicate diverse variations in the chemical profiles and insecticidal efficacies of P. yunnanense and P. boehmeriifolium EOs, providing more experimental evidence for the use of the Piper plants.