Evaluation of resistance to temephos insecticide in Culex pipiens pipiens larvae collected from three districts of Tunisia

Development and characterization of nanoemulsions loaded with essential oil and β-cypermethrin and their bioefficacy on insect pest of economic and medical importance

BACKGROUND

The development of novel and ecofriendly tools plays an important role in insect pest management. Nanoemulsions (NEs) based on essential oils (EOs) offer a safer alternative for human health and the environment. This study aimed to elaborate and evaluate the toxicological effects of NEs containing peppermint or palmarosa EOs combined with β-cypermethrin (β-CP) using ultrasound technique.

RESULTS

The optimized ratio of active ingredients to surfactant was 1:2. The NEs containing peppermint EO combined with β-CP (NEs peppermint/β-CP) were polydisperse with two peaks at 12.77 nm (33.4% intensity) and 299.1 nm (66.6% intensity). However, the NEs containing palmarosa EO combined with β-CP (NEs palmarosa/β-CP) were monodisperse with a size of 104.5 nm. Both NEs were transparent and stable for 2 months. The insecticidal effect of NEs was evaluated against Tribolium castaneum and Sitophilus oryzae adults, as well as Culex pipiens pipiens larvae. On all these insects, NEs peppermint/β-CP enhanced pyrethroid bioactivity from 4.22- to 16-folds while NEs palmarosa/β-CP, from 3.90- to 10.6-folds. Moreover, both NEs maintained high insecticidal activities against all insects for 2 months, although a slight increase of the particle size was detected.

CONCLUSION

The NEs elaborated in this work can be considered as highly promising formulations for the development of new insecticides. © 2023 Society of Chemical Industry.

Culex pipiens distribution in Tunisia: Identification of suitable areas through Random Forest and MaxEnt approaches

BACKGROUND

Tunisia has experienced several West Nile virus (WNV) outbreaks since 1997. Yet, there is limited information on the spatial distribution of the main WNV mosquito vector Culex pipiens suitability at the national level.

OBJECTIVES

In the present study, our aim was to predict and evaluate the potential and current distribution of Cx. pipiens in Tunisia.

METHODS

To this end, two species distribution models were used, i.e. MaxEnt and Random Forest. Occurrence records for Cx. pipiens were obtained from adult and larvae sampled in Tunisia from 2014 to 2017. Climatic and human factors were used as predictors to model the Cx. pipiens geographical distribution. Mean decrease accuracy and mean decrease Gini indices were calculated to evaluate the importance of the impact of different environmental and human variables on the probability distribution of Cx. pipiens.

RESULTS

Suitable habitats were mainly distributed next to oases, in the north and eastern part of the country. The most important predictor was the population density in both models. The study found out that the governorates of Monastir, Nabeul, Manouba, Ariana, Bizerte, Gabes, Medenine and Kairouan are at highest epidemic risk.

CONCLUSIONS

The potential distribution of Cx. pipiens coincides geographically with the observed distribution of the disease in humans in Tunisia. Our study has the potential for driving control effort in the fight against West Nile vector in Tunisia.

Mosquito Vectors (Diptera: Culicidae) and Mosquito-Borne Diseases in North Africa

Mosquitoes (Diptera: Culicidae) are of significant public health importance because of their ability to transmit major diseases to humans and animals, and are considered as the world's most deadly arthropods. In recent decades, climate change and globalization have promoted mosquito-borne diseases' (MBDs) geographic expansion to new areas, such as North African countries, where some of these MBDs were unusual or even unknown. In this review, we summarize the latest data on mosquito vector species distribution and MBDs affecting both human and animals in North Africa, in order to better understand the risks associated with the introduction of new invasive mosquito species such as Aedes albopictus. Currently, 26 mosquito species confirmed as pathogen vectors occur in North Africa, including Aedes (five species), Culex (eight species), Culiseta (one species) and Anopheles (12 species). These 26 species are involved in the circulation of seven MBDs in North Africa, including two parasitic infections (malaria and filariasis) and five viral infections (WNV, RVF, DENV, SINV and USUV). No bacterial diseases have been reported so far in this area. This review may guide research studies to fill the data gaps, as well as helping with developing effective vector surveillance and controlling strategies by concerned institutions in different involved countries, leading to cooperative and coordinate vector control measures.

Bioactivities of rose-scented geranium nanoemulsions against the larvae of Anopheles stephensi and their gut bacteria

Anopheles stephensi with three different biotypes is a major vector of malaria in Asia. It breeds in a wide range of habitats. Therefore, safer and more sustainable methods are needed to control its immature stages rather than chemical pesticides. The larvicidal and antibacterial properties of the Pelargonium roseum essential oil (PREO) formulations were investigated against mysorensis and intermediate forms of An. stephensi in laboratory conditions. A series of nanoemulsions containing different amounts of PREO, equivalent to the calculated LC₅₀ values for each An. stephensi form, and various quantities of surfactants and co-surfactants were developed. The physical and morphological properties of the most lethal formulations were also determined. PREO and its major components, i.e. citronellol (21.34%), L-menthone (6.41%), linalool (4.214%), and geraniol (2.19%), showed potent larvicidal activity against the studied mosquitoes. The LC_50/90 values for mysorensis and intermediate forms were computed as 11.44/42.42 ppm and 12.55/47.69 ppm, respectively. The F48/F44 nanoformulations with 94% and 88% lethality for the mysorensis and intermediate forms were designated as optimized formulations. The droplet size, polydispersity index, and zeta-potential for F48/F44 were determined as 172.8/90.95 nm, 0.123/0.183, and -1.08/-2.08 mV, respectively. These results were also confirmed by TEM analysis. Prepared formulations displayed antibacterial activity against larval gut bacteria in the following order of decreasing inhibitory: LC₉₀, optimized nanoemulsions, and LC₅₀. PREO-based formulations were more effective against mysorensis than intermediate. Compared to the crude PREO, the overall larvicidal activity of all nanoformulations boosted by 20% and the optimized formulations by 50%. The sensitivity of insect gut bacteria may be a crucial factor in determining the outcome of the effect of toxins on target insects. The formulations designed in the present study may be a good option as a potent and selective larvicide for An. stephensi.