Activity of carboxylesterases, glutathione-S-transferase and monooxygenase on Rhipicephalus microplus exposed to fluazuron

Insecticidal potential of a Consolida ajacis extract and its major compound (ethyl linoleate) against the diamondback moth, Plutella xylostella

The diamondback moth (Plutella xylostella) is one of the most destructive lepidopteran pests of cruciferous vegetables. However, DBM has developed resistance to current chemical and biological insecticides used for its control, indicating the necessity for finding new insecticides against it. Bio-insecticides derived from plant extracts are eco-friendly alternatives to synthetic pesticides. The aims of this study were to evaluate the insecticidal activity of Consolida ajacis seed extracts against DBM, the underlying mechanism of the control effect of promising extracts, and the identification of the main insecticidal compounds of these extracts. The results showed that ethyl acetate extract of C. ajacis seed exhibited strong contact toxicity (LC50: 5.05 mg/mL), ingestion toxicity, antifeedant, and oviposition deterrent activities against DBM, among the extracts evaluated. At 72 h, glutathiase, acetylcholinesterase, carboxylesterase, peroxidase, and superoxide dismutase activities were inhibited, but catalase activity was activated. The main compound identified from the extract was ethyl linoleate, which had the most significant insecticidal activity on the diamondback moths. This study's findings provide a better understanding of the insecticidal activity of ethyl acetate extract obtained from C. ajacis and its main component (ethyl linoleate). This will help in the development of new insecticides to control DBM.

A novel multi-criteria framework for optimizing ecotoxicological effects and human health risks of neonicotinoid insecticides: Characterization, assessment and regulation strategies

The rapid increase of neonicotinoid insecticides (NNIs) leads to the resistance to target organisms and risks to non-target organisms in the ecosystem. Thus, we designed a multi-criteria framework for resistance to target organisms, exposure risks to non-target organisms under spraying and soil or seed treatment scenarios, and ruled out the NNIs on the priority control lists. The resistance and cross-resistance, as well as the toxicity (i.e., acute, chronic, and combined toxicities) were characterized and evaluated. Results showed that the cross-resistance between two NNIs (i.e., CLO and FLU) was 1.8 times higher than their single resistance. A medium to extra-high toxicity level of NNIs was found in non-target organisms. Regulation strategies for NNIs resistance and toxicity were also proposed. The best synergist blocking and control scheme for resistance and toxicity was screened out when three main synergists (i.e., TPP: DEM: PBO) with the ratio of 1:1:1. Four NNIs (i.e., NPM, IMI, ACE, TMX) used in grain crops and six NNIs (i.e., NPM, IMI, ACE, TMX, CLO, THI) used in vegetable crops were determined as the ruled-out pesticides on the priority control lists. This study highlights the adverse effects of NNIs on the ecosystem and human health which should not be overlooked.

Acaricidal activity of Cinnamomum cassia (Chinese cinnamon) against the tick Haemaphysalis longicornis is linked to its content of (E)-cinnamaldehyde

Background

The tick Haemaphysalis longicornis (Neumann) is a well-known vector of numerous pathogens of veterinary and medical importance. Various control strategies, including the use of synthetic pesticides, have been developed to control this tick species. However, demand for effective and safe alternative pesticides is increasing due to the adverse effects associated with the intensive and injudicious use of synthetic pesticides, which include undesirable effects on non-target species and environmental pollution. Hence, the acaricidal activity of the extract and the essential oil of Cinnamomum cassia (Chinese cinnamon) and their major components, and the underlying mechanisms of this activity, were evaluated against unfed larvae and nymphs of H. longicornis.

Methods

The components of the extract and essential oil of C. cassia were determined by gas chromatography-mass spectrometry, and their larvicidal and nymphicidal activity were evaluated using the larval and nymphal packet test. The underlying detoxification mechanism was elucidated by targeting in vivo esterase and monooxygenase activity, and the toxicological effect was assessed on non-target Tenebrio molitor and Harmonia axyridis by topical application in open Petri dishes.

Results

(E)-cinnamaldehyde was the predominant component of the extract (50.79%) and essential oil (89.95%). The 50% lethal concentration (LC₅₀) for larvae and nymphs treated with the extract was 11.56 and 49.18 mg/mL, respectively. The essential oil, (E)-cinnamaldehyde and fenvalerate exhibited acaricidal activity, with LC₅₀ values of 3.81, 3.15, and 0.14 mg/mL, respectively, against the larvae, and 21.31, 16.93, and 1.89 mg/mL, respectively, against the nymphs. (E)-cinnamaldehyde significantly increased esterase and monooxygenase activity in both larvae and nymphs. Unlike fenvalerate, C. cassia essential oil and (E)-cinnamaldehyde did not cause mortality of T. molitor or H. axyridis adults.

Conclusions

This study demonstrates that C. cassia essential oil and (E)-cinnamaldehyde have the potential to be developed into botanical-based larvicidal and nymphicidal agents for tick control.

Graphical abstract

Benzoylphenyl ureas as veterinary antiparasitics. An overview and outlook with emphasis on efficacy, usage and resistance

Six benzoylphenyl ureas are currently used in formulations approved as veterinary medicines: diflubenzuron for fly control mainly on cattle, lice and blowfly strike control on sheep, and lice control on farmed salmonids; lufenuron for flea control on dogs and cats and for lice control on farmed salmonids; triflumuron for lice and blowfly strike control on sheep; fluazuron for tick control on cattle; teflubenzuron for lice control on farmed salmon; and novaluron for fly and tick control on cattle and for flea control on dogs. Resistance to diflubenzuron and triflumuron has already been reported for sheep body lice and blowflies, and to fluazuron in cattle ticks. These and other minor veterinary usages, as well as the current status of resistance, are reviewed and perspectives for future opportunities are discussed based on unexplored potentials and threats posed by future resistance development.