Photosensitizers in the fight against ticks: safranin as a novel photodynamic fluorescent acaricide to control the camel tick Hyalomma dromedarii (Ixodidae).

Ticks transmit more pathogen species than any other group of blood-feeding arthropods worldwide, affecting humans, livestock, and companion animals. Hyalomma dromedarii is the predominant tick species infesting camels, and its effective control is of pivotal importance. In this research, we compared the phytoefficacy of safranin (SF), a fluorescent dye applied as an acaricide for the first time, to that of tetramethrin (TM) against engorged females of H. dromedarii through in vitro immersion bioassays. Furthermore, the effect of SF exposure was evaluated on the reproductive potential of surviving tick females. Different concentrations of SF (0.03, 0.06, 0.3, 1, and 4 % w:v) and TM (0.03, 0.13, 0.5, 2, and 4 %) were prepared in distilled water and administered to engorged females of H. dromedarii. SF-treated ticks were illuminated with a light source for 30 min post-treatment (PT). Photophysical properties of SF were studied, and the relative efficacy of the used light source and sunlight was calculated. Results showed that the minimum least concentration that causes 100 % acaricidal effect was 4 % PT with SF and TM, for 8 and 48 h, respectively. LC50 values 8 and 24 h PT were 0.08, 0.03 and 0.78, 0.20 %, respectively. Comparing LC50 and LC90 2 h PT, SF was 33 and 22 times more potent than TM. LT50 of 4 % SF and TM were 0.80 and 2.17 h, respectively. Treatment with the lowest concentrations of SF and TM induced reduction of the number of ovipositing females, eggs per female, ticks laying viable eggs, and hatched eggs. Overall, our results highlighted that SF is highly effective if compared to TM, allowing use to candidate it for the development of novel and safer acaricides.

RNAi-mediated silencing of an egg-specific gene Nllet1 results in hatch failure in the brown planthopper.

BACKGROUND: The brown planthopper (BPH) is one of the most destructive agricultural pests in Asia. RNA interference (RNAi)-mediated pest management has been under development for years, and the selection of appropriate target genes is important for pest-targeted RNAi. C-type lectins (CTLs) are a class of genes that perform a variety of functions, such as the regulation of growth and development. RESULTS: A CTL-S protein named Nllet1, containing a single calcium ion (Ca2+ )-dependent carbohydrate-binding domain (CRD) with a conserved triplet motif QPD was identified and functionally characterized in BPH. Expression profiles at both the transcriptional and translational levels show that Nllet1 accumulates during the serosal cuticle (SC) formation period. Immunofluorescence and immunogold labeling further demonstrated that Nllet1 is located in the serosal endocuticle (en-SC). Maternal RNAi-mediated silencing of Nllet1 disrupted the SC structure, accompanied by a loss of the outward barrier and 100% embryo mortality. Injection of 10 ng dsNllet1 or dsNllet1' per female adult BPH resulted in a total failure of egg hatching. CONCLUSION: Nllet1 is essential for SC formation and embryonic development in BPH, which helps us understand the important roles of CTL-Ss. Additionally, BPH eggs show high sensitivity to the depletion of Nllet1. This study indicates that Nllet1 is a promising candidate gene that can be used to develop RNAi-based control strategies at the BPH egg stage, and it can also be used as a target for developing novel ovicides. © 2022 Society of Chemical Industry.

Fern-synthesized silver nanocrystals: Towards a new class of mosquito oviposition deterrents?

Mosquitoes act as vectors of devastating pathogens and parasites, representing a key threat for millions of humans and animals worldwide. Eco-friendly control tools are urgently required. We proposed a novel method of fern-mediated biosynthesis of silver nanoparticles (AgNP) using Dicranopteris linearis, acting as a reducing and capping agent. AgNP were characterized by UV-vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), zeta potential and particle size analysis. In mosquitocidal assays, the LC50 of D. linearis extract against Aedes aegypti ranged from 165.213 (larva I) to 255.055ppm (pupa). LC50 of D. linearis-synthesized AgNP ranged from 18.905 (larva I) to 29.328ppm (pupa). In the field, the application of D. linearis extract and AgNP (10×LC50) led to 100% larval reduction after 72h. Smoke toxicity experiments conducted against A. aegypti adults showed that D. linearis leaf-, stem- and root-based coils evoked mortality rates comparable to the permethrin-based positive control (58%, 47%, 34%, and 48% respectively). In ovicidal experiments, egg hatchability was reduced by 100% after treatment with 25ppm of AgNP and 300ppm of D. linearis extract. Interestingly, oviposition deterrent assays highlighted that 100ppm of fern extract reduced oviposition rates of more than 65%, while 10ppm of fern-fabricated AgNP reduced oviposition rates of more than 70% in A. aegypti (OAI were -0.52 and -0.55, respectively). Overall, our results highlighted that D. linearis-synthesized AgNP could be useful candidates to develop nano-formulated oviposition deterrents effective against dengue vectors.