Investigation of insecticidal activity of two Rhododendron species on stored-product insects.

This study was designed to investigate the insecticidal activity of the essential oils (EOs) and extracts from Rhododendron rufum and Rhododendron przewalskii. The EOs were extracted from the leaves of R. Rufum and R. przewalskii by hydro-distillation and their chemical components were analyzed by gas chromatography-mass spectrometry (GC-MS). The repellency, contact toxicity and antifeedant activity of the EOs and extracts were evaluated against Sitophilus oryzae and Tribolium castaneum along with those of their main components. A total of nine compounds were identified from the EO of R. Rufum, and the most abundant component was myristicin (79.72%). The EO of R. Rufum exhibited repellent activities at different levels and its main compound myristicin showed contact toxicity and repellent effects against S. oryzae and T. castaneum. Meanwhile, by bioassay-guided fractionation, four compounds with strong antifeedant activities against T. castaneum, 24-methylenecycloartanyl-2'E, 4'Z-tetradecadienoate (1), methyl thyrsiflorin B acetate (2), friedelin (3) and Excoecarin R1 methyl ester (4) were separated and identified from the ethanol extract of R. przewalskii for the first time. Considering the significant anti-insect activities, the EOs and extracts of R. Rufum and R. przewalskii might be used in integrated pest strategies, establishing a good perspective for the comprehensive use of natural plant resources of Rhododendron genus.

Contact toxicity and repellence of essential oil from Senecio scandens and its major components against three stored product insects.

The objective of this work was to investigate the chemical compositions of the essential oil (EO) extracted from Senecio scandens by hydrodistillation and their insecticidal activities against Tribolium castaneum, Lasioderma serricorne and Liposceis bostrychophila. The chemical profile of the EO were analyzed by gas chromatography-mass spectrometry (GC-MS), and 20 compounds were identified which accounted for 88.03% of the total EO. Five major compounds identified in the EO were assayed against the three stored product insects. The EO showed strong contact toxicity to T. castaneum (LD50 = 18.01 µg/adult), L. serricorne (LD50 = 20.11 µg/adult) and L. bostrychophila (LD50 = 72.14 µg/cm2). Among all compounds, geraniol showed the contact toxicity against L. serricorne and L. bostrychophila with LD50 values of 15.82 µg/adult and 26.64 µg/cm2. The EO and its five chemical compounds also exhibited different level of potential repellence to the three stored product insects.

Chemical composition of essential oils from four Rhododendron species and their repellent activity against three stored-product insects.

The objective of this work was to analyze four essential oils (EOs) from Rhododendron species in China and evaluate their repellent activity against Tribolium castaneum, Lasioderma serricorne, and Liposcelis bostrychophila adults. These four EOs from Rhododendron species, including R. capitatum, R. przewalskii, R. mucronulatum, and R. micranthum, were obtained by hydrodistillation. Major components of four EOs were identified as sesquiterpenoids by GC-MS. The relatively high components included cedrene (22.20%), borneol (36.64%), 4-(2,3,4,6-tetramethylphenyl)-3-buten-2-one (27.74%), and germacrene D (27.60%). Repellent activity of EOs from Rhododendron species was investigated against T. castaneum, L. serricorne, and L. bostrychophila adults for the first time. In this study, EOs had demonstrated their repellent activities against three stored-product insects in 2- and 4-h exposure. The above results can not only provide comprehensive utilization of plant resources of Rhododendron genus but also establish a very good perspective of novel application to control stored-product insects.

Supercritical carbon dioxide extract of Cinnamomum cassia bark: toxicity and repellency against two stored-product beetle species.

The extract from Cinnamomum cassia Presl bark was obtained with supercritical CO2 fluid extraction (SFE). Chemical components of the SFE extract were characterized by GC-MS spectrometry. The repellency and contact toxicity of the SFE extract were evaluated against the adults of Tribolium castaneum and Lasioderma serricorne along with those of its two main compounds. The results of GC-MS analysis indicated that 33 volatile constituents were identified from the extract. The main components included trans-cinnamaldehyde (32.1%), 3,3-dimethylhexane (10.6%) and 2,4-di-tert-butylphenol (7.9%). Testing results showed that the SFE extract had potent contact toxicity against T. castaneum and L. serricorne with LD50 values of 3.96 and 23.89 µg/adult, respectively. LD50 values of trans-cinnamaldehyde against T. castaneum and L. serricorne were 5.78 and 3.24 µg/adult, respectively. Additionally, percentage repellency values of the SFE extract and trans-cinnamaldehyde against T. castaneum and L. serricorne were rather high (PR = 100% and PR > 90%, respectively) at 78.63 and 15.73 nL/cm2 at 2 h post-exposure. 2,4-Di-tert-butylphenol showed some repellency against both beetle species. Considering its insecticidal and repellent effects, the SFE extract from C. cassia bark might be used in integrated pest management programs for T. castaneum and L. serricorne.

3-(2,4-Dichloro-phen-yl)-5-(4-fluoro-phen-yl)-2-phenyl-7-(trifluoro-meth-yl)pyrazolo-[1,5-a]pyrimidine.

In the title compound, C(25)H(13)Cl(2)F(4)N(3), there are four planar systems, viz. three benzene rings and a pyrazolo-[1,5-a]pyrim-idine system [r.m.s. deviation = 0.002 Å]. The dihedral angle between the dichloro-phenyl ring and the unsubstituted phenyl ring is 69.95 (5)°, while that between the fluoro-phenyl ring and the unsubstituted phenyl ring is 7.97 (10)°. The crystal packing is dominated by van der Waals inter-actions. A Cl⋯Cl inter-action of 3.475 (3) Šalso occurs.