Zhixiang Zhang

Insecticidal, fumigant, and repellent activities of sweet wormwood oil and its individual components against red imported fire ant workers (Hymenoptera: Formicidae).

Abstract In total, 29 compounds from sweet wormwood ( Artemisia annua L.) oil were identified using gas chromatography–mass spectrometry. The five active components were d -camphor, linalool, cineole, α-terpineol, and l (−)-borneol. The effectiveness of A. annua oil, as well as d -camphor, linalool, cineole, α-terpineol, and l (−)-borneol, as fumigants, contact insecticides, and repellents, were tested on the red imported fire ant Solenopsis invicta Buren. The results indicated that A. annua oil has no significant topical toxicity; however, the spray contact test revealed that it has strong insecticidal activity and the inhibitory effect is stronger during closed exposure than during open exposure. In the fumigant test, cineole and d -camphor exhibited strong fumigant toxicity on minor and major S. invicta workers. They also caused 100% mortality at 5, 3, 2, and 1u2009mg/centrifuge tube but not at 0.5u2009mg/centrifuge tube. The mortality rates of linalool, α-terpineol, and l (−)-borneol exceeded 80% at 5, 3, and 2u2009mg/centrifuge tube. In the repellent test, cineole and d -camphor showed significant repellency at 100, 10, and 1u2009mg/kg. However, linalool, α-terpineol, and l (−)-borneol significantly facilitated digging at 10 and 1u2009mg/kg.

Effect of two formulations on the decline curves and residue levels of rotenone in cabbage and soil under field conditions.

The dissipation and residue levels of rotenone with suspension concentrate (SC) as well as water dispersible granule (WDG) formulations in cabbage and soil were investigated under field conditions. The decline curves of rotenone residues in cabbage and soil corresponded with first-order kinetics. The dissipation rate of rotenone in cabbage was faster than that in soil. The half-lives of the SC formulations in cabbage and soil were 1.14d to 1.85d and 2.26d to 3.98d, respectively. For the WDG formulation, the values were 1.33d to 1.96d and 2.41d to 3.38d. Less spraying, lower dosage, and longer pre-harvest intervals could reduce terminal residue levels. Terminal residues below the MRL (0.5mg kg(-1)) were achieved after pre-harvest intervals of 3d at either once (45g a.i. ha(-1)) or twice (90g a.i. ha(-1)) the recommended dosage. The different dissipation processes of rotenone in cabbage and soil under field conditions could be attributed to the different climate and soil properties, and the types of formulation had no apparent effect on half-life. Formulation type affected the initial concentrations and finally led to different terminal residues. Prolonged pre-harvest intervals are necessary to ensure that the products are sufficiently safe for consumption.

Dissipation and Residue of Rotenone in Cabbage and Soil Under Field Conditions

Rotenone dissipation and terminal residue in cabbage and soil under field conditions were determined by high-performance liquid chromatography. The dissipation rates of rotenone were described using first-order kinetics. The half-lives ranged from 0.89 to 1.55xa0days in cabbage and 1.98 to 2.76 days in soil. Prolonged pre-harvest interval times ensure that the cabbage is safe for consumption. Temperature and the physico-chemical properties of the soil were identified as the key factors affecting rotenone degradation in cabbage and soil under field conditions.

Fumigant Toxicity and Repellence Activity of Camphor Essential Oil from Cinnamonum camphora Siebold Against Solenopsis invicta Workers (Hymenoptera:Formicidae)

The red imported fire ant (RIFA) Solenopsis invicta Buren causes severe damage to humans and animals as well as the environment. Chemical treatment is the main strategy of RIFA management, which also is potentially toxic to the environment. Plant essential oils (EOs) are considered as potential substance that can be used to control insects. This study aimed to identify the chemical composition of camphor EO and investigate the insecticidal activity on RIFAs. The chemical composition of the EO was analyzed by gas chromatography/mass spectrometry and gas chromatography with flame ionization detection. Results revealed that 36.61% camphor and 30.05% cineole were the major components. The insecticidal activity of camphor EO was assessed against RIFA workers by conducting two different bioassays: fumigant toxicity and repellence. Fumigant toxicity assay results showed that the lethal dose (LC50) of the EO at 24u2009h was 1.67 and 4.28u2009μg/ml for minor and major workers, respectively; knockdown time (KT50) was 10.82 and 14.73u2009h. At 2.55u2009μg/ml, the highest average mortality of the ants was 84.89% after 72u2009h. Camphor EO exhibited fumigant toxicity against minor and major workers as indicated by the effects on attacking, feeding, and climbing behaviors. This EO was also strongly repellent to the two size workers of the colony as observed in their behavior against Tenebrio molitor treated with 5u2009µl EO. The fumigant toxicity and repellence of camphor EO against RIFA indicated that this substance could be a potential alternative for the development of eco-friendly products used to control pests.

Dissipation and residue of triforine in strawberry and soil

Two independent field trials were performed in Guangdong and Hubei, China in 2011 to investigate the dissipation and residue levels of triforine in strawberry and soil. A fast and simple method using gas chromatography with electron capture detector was developed and validated to determine triforine levels in strawberry and soil. The average recovery of triforine in strawberry ranged from 87.46 to 104.32xa0% with a relative standard deviation (RSD) of 0.72 to 4.54xa0%; that in soil ranged from 83.82 to 103.01xa0% with an RSD of 3.89 to 4.36xa0%. The limit of quantification of the proposed method was 0.01xa0mg/kg for both strawberry and soil. The results suggest that the triforine dissipation curves followed the first-order kinetic. The half-lives of triforine in strawberry from Guangdong and Hubei were 3.58 and 4.42xa0days, respectively; those in soil were 3.53 and 4.10xa0days, respectively. The terminal residues of triforine in strawberry ranged from 0.032 to 0.264xa0mg/kg at preharvest intervals of 0.5, 1, and 3xa0days. These values are lower than the maximum residue limit of 1xa0mg/kg in strawberry set by the Codex Alimentarius Commission.

Laboratory evaluation of aqueous leaf extract of Tephrosia vogelii against larvae of Aedes albopictus (Diptera: Culicidae) and non-target aquatic organisms

Mosquito control using insecticides has been the most successful intervention known to reduce malaria prevalence or incidence. However, vector control is facing a threat due to the emergence of resistance to synthetic insecticides. Insecticides of botanical origin may serve as suitable alternative biocontrol techniques in the future. In this research, the leaf aqueous leachate of Tephrosia vogelii was evaluated for its toxicity against larvae of the most invasive mosquito worldwide, Aedes albopictus (Diptera: Culicidae), and toward adults of the water flea, Daphnia magna (Cladocera: Crustacea) and Oreochromis niloticus, two non-target aquatic organisms that share the same ecological niche of A. albopictus. The leaf aqueous leachate of T. vogelii was evaluated against fourth-instar larvae, non-blood fed 3-5 days old laboratory strains of A. albopictus under laboratory condition. In addition, the objective of the present work was to study the environmental safety evaluation for aquatic ecosystem. Mortality was then recorded after 7d exposure. The leaf aqueous leachate of T. vogelii showed high mosquitocidal activity against larvae of A. albopictus, with a LC50=1.18μg/mL. However, it had a remarkable acute toxicity also toward adults of the non-target arthropod D. magna, with a LC50=0.47μg/L and O. niloticus with a LC50=5.31μg/L. The present findings have important implications in the practical control of mosquito larvae in the aquatic ecosystem, as the medicinal plants studied are commonly available in large quantities. The extract could be used in stagnant water bodies for the control of mosquitoes acting as vector for many communicable diseases.

Uptake of soil-applied thiamethoxam in orange and its effect against Asian citrus psyllid in different seasons: Effect of thiamethoxam against Asian citrus psyllid by soil drench

BACKGROUNDnAsian citrus psyllid (ACP), Diaphorina citri Kuwayama, is an important pest of citrus worldwide because it transmits the bacteria causing huanglongbing (HLB). We investigated the effects and persistence of two soil application rates of thiamethoxam on ACP populations in two flushing seasons in the field. Thiamethoxam and clothianidin residues in the fruit were detected to evaluate food safety.nnnRESULTSnSoil application of 50% thiamethoxam water-dispersible granules at concentrations of 4 and 10 g tree-1 significantly decreased ACP populations, and there was a positive correlation between control efficacy and the persistence of thiamethoxam and clothianidin in leaves, providing longer-term protection for up to 90 days in the fall compared with 60 days in the spring. Higher thiamethoxam and clothianidin amounts were observed in new leaves than in old leaves. Thiamethoxam and clothianidin residues at a high rate in fruit were 0.012 and 0.010 mg kg-1 at harvest, respectively, and neither insecticides was detectable at low rates.nnnCONCLUSIONSnThese results demonstrate that soil-applied thiamethoxam plays a role in defending ACP, and provides an extended period of control efficacy. This knowledge could provide a reference for the control of ACP by soil application of thiamethoxam to reduce HLB spread.

Residue and distribution of triforine in different cultivars and fruit periods of watermelon under field conditions

The dissipation of triforine in the immature and mature fruit periods was investigated under field conditions. Residue levels of triforine in watermelon were determined by gas chromatography with an electron capture detector (GC-ECD). The decline curves of triforine residues in the watermelon corresponded with first-order kinetics. The half-lives of triforine in Dark Belle and Shiny Boy were 2.10-2.57 days and 2.31-2.67 days respectively. Meanwhile, the half-lives of triforine in the immature and mature fruit periods were 1.69-2.04 days and 2.89-3.85 days, respectively. In the terminal residue experiment, the terminal residues of triforine in the watermelon flesh and peel were below 0.01u202fmg/kg to 0.05u202fmg/kg and 0.03u202fmg/kg to 0.36u202fmg/kg, respectively. The dissipation rates of triforine varied in different cultivars of watermelon, and even in the same cultivar, the half-lives of triforine significantly varied in the different fruit periods. Although triforine is a fungicide within the suction, the terminal residues in the peel and flesh were very significant.

Insecticidal activity of the methanol extract of Pronephrium megacuspe (Thelypteridaceae) and its active component on Solenopsis invicta (Hymenoptera: Formicidae)

Abstract Baits were used to investigate the toxicity of methanol extracts from the fern Pronephrium megacuspe (Thelypteridaceae) on workers of the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae). The methanol extract of P. megacuspe had toxic effects on workers. With macrergates, the LC50 values of the methanol extract and ethyl acetate fraction were 524.0 and 145.9 μg/g, respectively, after 48 h of treatment and 362.5 and 99.0 μg/g, respectively, after 72 h of treatment. With micrergates, the LC50 values of the methanol extract and ethyl acetate fraction were 321.9 and 90.0 μg/g, respectively, after 48 h of treatment and 235.4 and 79.1 μg/g, respectively, after 72 h of treatment. NMR spectral data revealed that the isolated compound from the ethyl acetate soluble fraction of methanol extract was phenol-3-O-beta-D-glucoside. The LC50 values of this compound with macrergates after 48 and 72 h were 21.6 and 9.7 μg/g, respectively. Similarly, the LC50 values of this compound with micrergates after 48 and 72 h were 3.4 and 2.4 μg/g, respectively. A low dose of methanol extract and ethyl acetate fractions of P. megacuspe, and of phenol-3-Obeta-D-glucoside diminished the walking and grasping abilities of S. invicta micrergates and macrergates.