Ultrasound-assisted nanoemulsion of Trachyspermum ammi essential oil and its constituent thymol on toxicity and biochemical aspect of Aedes aegypti.

Aedes aegypti is the main vector of yellow fever, chikungunya, Zika, and dengue worldwide and is managed by using chemical insecticides. Though effective, their indiscriminate use brings in associated problems on safety to non-target and the environment. This supports the use of plant-based essential oil (EO) formulations as they are safe to use with limited effect on non-target organisms. Quick volatility and degradation of EO are a hurdle in its use; the present study attempts to develop nanoemulsions (NE) of Trachyspermum ammi EO and its constituent thymol using Tween 80 as surfactant by ultrasonication method. The NE of EO had droplet size ranging from 65 ± 0.7 to 83 ± 0.09 nm and a poly dispersity index (PDI) value of 0.18 ± 0.003 to 0.20 ± 0.07 from 1 to 60 days of storage. The NE of thymol showed a droplet size ranging from 167 ± 1 to 230 ± 1 nm and PDI value of 0.30 ± 0.03 to 0.40 ± 0.008 from 1 to 60 days of storage. The droplet shape of both NEs appeared spherical under a transmission electron microscope (TEM). The larvicidal effect of NEs of EO and thymol was better than BEs (Bulk emulsion) of EO and thymol against Ae. aegypti. Among the NEs, thymol (LC50 34.89 ppm) had better larvicidal action than EO (LC50 46.73 ppm). Exposure to NEs of EO and thymol causes the shrinkage of the larval cuticle and inhibited the acetylcholinesterase (AChE) activity in Ae. aegypti. Our findings show the enhanced effect of NEs over BEs which facilitate its use as an alternative control measure for Ae. aegypti.

Biocontrol potential of entomopathogenic nematodes for the sustainable management of Spodoptera frugiperda (Lepidoptera: Noctuidae) in maize.

BACKGROUND: The occurrence of Spodoptera frugiperda (J.E. Smith) in Asia was reported for the first time from Karnataka in 2018. This pest is widely distributed in India, causing significant damage to maize. Management of this recent invasive pest in maize-growing regions of India relies on chemical control. Resistance is the greatest obstacle to the successful use of chemical insecticides to control this pest. Indiscriminate use of chemical insecticides destroys beneficial natural enemies, therefore effective and sustainable alternative control strategies are needed. In this case, the use of biological control agents is the alternative option to mitigate this pest. Thus, this study aimed to select virulent entomopathogenic nematodes (EPNs) isolates based on the laboratory assay and further to test the efficacy of virulent isolates in the field conditions along with commonly used chemical insecticide emamectin benzoate against S. frugiperda. RESULTS: Laboratory results revealed that both Heterorhabditis indica 1 NBAIIH38 and Steinernema carpocapsae NBAIRS59 caused 100% mortality in third- and fourth-instar larvae of S. frugiperda, while these two species caused 85% and 72% mortality in pupae, respectively. When pupae of S. frugiperda were exposed to EPNs, pupae died after metamorphosis to malformed adults. All the nematode species were able to penetrate and reproduce within S. frugiperda larvae, but the reproduction rate for Heterorhabditids was higher than that of Steinernematids. Field trial results showed that H. indica 1 NBAIIH38 significantly reduced the number of larvae and leaf damage scores compared to S. carpocapsae NBAIRS59. Emamectin benzoate was more effective in reducing the larval population compared to EPN species. The cob yield was significantly higher in EPN- and emamectin benzoate-treated plots than in untreated control plots. CONCLUSION: Overall, these experiments suggest H. indica 1 NBAIIH38 is a promising biocontrol agent against S. frugiperda in maize production. © 2022 Society of Chemical Industry.

Nanomaze Lure: Pheromone Sandwich in Graphene Oxide Interlayers for Sustainable Targeted Pest Control.

The indiscriminate use of pesticides leads to irreparable damage to the ecosystem, which motivates for sustainable alternatives like pheromone-assisted pest management. The tomato pinworm Tuta absoluta is a major threat to tomato cultivation. Moreover, its green management technology uses a pheromone trap that has a short field life. To overcome this problem, a pheromone composite with graphene oxide (GO) and amine-modified graphene oxide (AGO) that can extend the diffusion path has been developed. The composite stimulates an effective electrophysiological response in the antenna, which results in trapping of a significantly higher number of insects as compared to the commercial septa, thus qualifying it for field evaluation. Compared to AGO, the GO composite has pheromones assembled into a multilayer, which increases the pheromone diffusion path. This in turn resulted in the extension of the pheromone life that proportionally increased the pest trapped. This technique will be beneficial to farmers as they have longer field efficacy to keep the pest damage low in an environmentally friendly manner.

Electrophysiological, behavioural and biochemical effect of Ocimum basilicum oil and its constituents methyl chavicol and linalool on Musca domestica L.

Ocimum basilicum essential oil (EO) was evaluated for its biological effects on M. domestica. Characterization of O. basilicum EO revealed the presence of methyl chavicol (70.93%), linalool (9.34%), epi-α-cadinol (3.69 %), methyl eugenol (2.48%), γ-cadinene (1.67%), 1,8-cineole (1.30%) and (E)-ß-ocimene (1.11%). The basil EO and its constituents methyl chavicol and linalool elicited a neuronal response in female adults of M. domestica. Adult female flies showed reduced preference to food source laced with basil EO and methyl chavicol. Substrates treated with EO and methyl chavicol at 0.25% resulted in an oviposition deterrence of over 80%. A large ovicidal effect was found for O. basilicum EO (EC50 9.74 mg/dm3) followed by methyl chavicol (EC50 10.67 mg/dm3) and linalool (EC50 13.57 mg/dm3). Adults exposed to EO (LD50 10.01 µg/adult) were more susceptible to contact toxicity than to methyl chavicol and linalool (LD50 13.62 µg/adult and LD50 43.12 µg/adult respectively). EO and its constituents methyl chavicol and linalool also induced the detoxifying enzymes Carboxyl esterase (Car E) and Glutathione S - transferases (GST).

Toxicity, behavioural and biochemical effect of Piper betle L. essential oil and its constituents against housefly, Musca domestica L.

Housefly, Musca domestica L. is a pest of public health importance and is responsible for spreading diseases like typhoid, diarrhoea, plague etc. Indiscriminate reliance on synthetic insecticides has led to development of insecticide resistance and ill effect to humans and nontarget animals. This demands an alternative and safer pest control option. This study evaluates the biological effect of Piper betle L essential oil and its constituent eugenol, eugenol acetate, and ß - caryophyllene on the housefly. The major components present in P. betel EO were safrole (44.25%), eugenol (5.16%), ß -caryophyllene (5.98%), ß -selinene (5.93%), α-selinene (5.27%) and eugenol acetate (9.77%). Eugenol caused 4.5fold higher ovicidal activity (EC50 86.99 µg/ml) than P. betle EO (EC50 390.37 µg/ml). Eugenol caused fumigant toxicity to adults (LC50 88.38 mg/dm3). On contact toxicity by topical application, eugenol acetate, eugenol and ß-caryophyllene caused higher mortality to larval and adult stages than EO. FESEM (Field Emission Scanning Electron Microscope) images reveal that exposure to P. betle EO causes the shrinkage of the larval cuticle. Both EO and eugenol induced the detoxifying enzymes Carboxyl esterase (Car E) and Glutathione S - transferases (GST) in larvae and adults. EO and eugenol at 0.2% caused effective repellence and oviposition deterrence to M. domestica adults and this merits their use as alternative strategy to manage M. domestica.

Acetylcholinesterase inhibition by biofumigant (Coumaran) from leaves of Lantana camara in stored grain and household insect pests.

Recent studies proved that the biofumigants could be an alternative to chemical fumigants against stored grain insect pests. For this reason, it is necessary to understand the mode of action of biofumigants. In the present study the prospectus of utilising Lantana camara as a potent fumigant insecticide is being discussed. Inhibition of acetylcholinesterase (AChE) by Coumaran, an active ingredient extracted from the plant L. camara, was studied. The biofumigant was used as an enzyme inhibitor and acetylthiocholine iodide as a substrate along with Ellman's reagent to carry out the reactions. The in vivo inhibition was observed in both dose dependent and time dependent in case of housefly, and the nervous tissue (ganglion) and the whole insect homogenate of stored grain insect exposed to Coumaran. The possible mode of action of Coumaran as an acetylcholinesterase inhibitor is discussed.