Rotenoids from Clitoria fairchildiana R. Howard (Fabaceae) seeds affect the cellular metabolism of larvae of Aedes aegypti L. (Culicidae).

Non-domesticated species may represent a treasure chest of defensive molecules which must be investigated and rescued. Clitoria fairchildiana R. Howard is a non-domesticated Fabacea, native from the Amazonian Forest whose seeds are exquisitely refractory to insect predation. Secondary metabolites from these seeds were fractionated by different organic solvents and the CH2Cl2 fraction (CFD - Clitoria fairchildiana dichloromethane fraction), as the most toxic to 3rd instar Aedes aegypti larvae (LC50 180 PPM), was subjected to silica gel chromatography, eluted with a gradient of CH2Cl2: MeOH and sub fractioned in nine fractions (CFD1 - CFD9). All obtained fractions were tested in their toxicity to the insect larvae. Two rotenoids, a 11α-O-ß-D-glucopyranosylrotenoid and a 6-deoxyclitoriacetal 11-O-n-glucopyranoside, were identified in the mixture of CFD 7.4 and CFD 7.5, and they were toxic (LC50 120 PPM) to 3rd instar Ae. aegypti larvae, leading to exoskeleton changes, cuticular detachment and perforations in larval thorax and abdomen. These C. fairchildiana rotenoids interfered with the acidification process of cell vesicles in larvae midgut and caused inhibition of 55% of V-ATPases activity of larvae treated with 80 PPM of the compounds, when compared to control larvae. The rotenoids also led to a significant increase in the production of reactive oxygen species (ROS) in treated larvae, especially in the hindgut region of larvae intestines, indicating a triggering of an oxidative stress process to these insects.

Myracrodruon urundeuva leaf lectin damages exochorionic cells and binds to the serosal cuticle of Aedes aegypti eggs.

In recent years, lectins have been identified as alternative agents against Aedes aegypti during the aquatic phases of its life cycle. For example, chitin-binding lectin from Myracrodruon urundeuva leaf (MuLL) can function as a larvicide. In this study, we investigated whether MuLL can also act as an ovicide against this insect. Aedes aegypti eggs were incubated with MuLL for 72 h to determine the concentration at which the hatching rate reduces by 50% (EC50). The effects of MuLL on the egg surface structure were evaluated using scanning electron microscopy (SEM), and the possible interaction of MuLL with the internal structures of eggs and embryos was investigated using MuLL-fluorescein isothiocyanate (FITC) conjugate. MuLL acted as an ovicidal agent with an EC50 of 0.88 mg/mL. The SEM analysis revealed that eggs treated with MuLL for 24 and 48 h no longer had tubercles and did not show a well-defined exochorionic network. In addition, deformation and degeneration of the surface were observed after 72 h. Fluorescence microscopy showed that MuLL penetrated the eggs 48 h after incubation and was detected in the upper portion of the embryo's gut. After 72 h, MuLL was observed in the serosal cuticle and digestive tract. In conclusion, MuLL can function as an ovicidal agent against A. aegypti through damage to the surface and internal structures of the eggs.

Effects of a solid formulation containing lectin-rich fraction of Moringa oleifera seeds on egg hatching and development of Aedes aegypti larvae.

The measures currently used to minimize the spread of arboviruses, comprising dengue, Chikungunya, and Zika virus, involve controlling the size of population of the mosquito Aedes aegypti. However, the search for formulations containing new insecticides is gaining pace due to reports of mosquito populations showing resistance to commonly used compounds. In this study, tablets containing a protein fraction of Moringa oleifera seeds enriched in the WSMoL lectin, known to show larvicidal and ovicidal activities against A. aegypti, were developed. The compatibility between the fraction and the excipients used in obtaining the tablets was evaluated by thermogravimetry (TG), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) absorption spectroscopy. The larvicidal and ovicidal activities of the resulting tablets [5%, 10%, and 15% (w/w) of the fraction] were evaluated, as well as their effect on mosquito oviposition. Assays were also performed using a placebo tablet. According to the TG, DSC, and FTIR results, the protein composition of the fraction did not change when mixed with the components of the formulation. Tablets containing 10% and 15% WSMoL-rich fraction caused mortality of 42.5% and 95% of the larvae after 48 h, respectively, with larvae incubated with these tablets showing reduced acetylcholinesterase activity. All tablets inhibited egg hatching after 72 h (36-74%), and tablets containing 15% fraction were found to exert a repellent effect on oviposition. Our results show that the formulation developed in this study interfered with the life cycle of A. aegypti, and thus show potential for use in the control of this mosquito.

Larvicidal activity of Maytenus guianensis (Celastraceae) against Aedes aegypti (Diptera: Culicidae)

Abstract INTRODUCTION: Bioprospection of plant products is used to discover new insecticides. METHODS: The larvicidal activity of ethanolic extract and triterpene (tingenone B) from the bark of Maytenus guianensis and their effect on pupation and emergence were evaluated against Aedes aegypti. RESULTS: Crude extract LC50 was 11.3 ppm and caused ejection of the larvae intestine; tingenone B LC50 was 14.8 ppm. Pupation was reduced by 20% and 10%, respectively; however, the emergence was not affected. CONCLUSIONS: The crude bark extract exhibited a higher larvicidal effect against the vector.

Evaluation of Larvicidal Efficacy of Ricinus communis (Castor) Plant Extract and Synthesized Green Silver Nanoparticles against Aedes albopictus.

BACKGROUND: Aedes mosquitoes are the most important group of vectors having ability of transmitting pathogens including arboviruses that can cause serious diseases like Chikungunya fever, Dengue fever and Zika virus in human. Biosynthesis and the use of green silver nanoparticles (AgNPs) is an important step in the search of reliable and ecofriendly control of these vectors. METHODS: In this study an aqueous leaves extract of Ricinus communis (castor) and silver nanoparticles (AgNPs) synthesized from this extract were evaluated as larvicidal agent for 2nd and 3rd instar larvae of the Aedes albopictus. Different concentrations (50, 100, 150, 200 and 250ppm) of plant extract and synthesized nanoparticles were prepared and applied on second and third instar larvae. The percent mortality was noted after 6, 12, 18, 24, 30, 36, 42 and 48H of exposure and subjected to probit analysis to calculate LC50 and LC90. RESULTS: Synthesized Ag+ nanoparticles were characterized by UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and energy-dispersive X-ray spectroscopy (XRD). The nanoparticles were more toxic against larvae of Ae. albopictus with LC50 value (49.43ppm) and LC90 value (93.65ppm) for 2nd instar larvae and LC50 (84.98ppm) and LC90 (163.89ppm) for 3rd instar larvae as compared to the plant extract (149.58ppm, 268.93ppm) and (155.58ppm, 279.93ppm) for 2nd and 3rd instar larvae of Ae. albopictus respectively after 48H. CONCLUSION: Our results suggest the extract of R. communis and synthesized nanoparticles as excellent replacement of chemical pesticides to control the vector mosquitoes.

Ovicidal lectins from Moringa oleifera and Myracrodruon urundeuva cause alterations in chorionic surface and penetrate the embryos of Aedes aegypti eggs.

BACKGROUND: Lectins from Moringa oleifera seeds (WSMoL), Myracrodruon urundeuva bark (MuBL), and heartwood (MuHL) are larvicidal agents against Aedes aegypti; in addition, WSMoL is an ovicidal agent against this mosquito. In this work, we evaluated the ovicidal activity of MuBL and MuHL by determining the concentrations that reduce the hatching rates by 50% in 72 h (EC50 ). The effects of WSMoL, MuBL, and MuHL on the ultrastructure of the eggs' surface were assessed by scanning electron microscopy (SEM). In addition, the ability of these lectins to penetrate the eggs was investigated by using conjugates of the lectins with fluorescein isothiocyanate (FITC). RESULTS: MuBL and MuHL were ovicidal agents with EC50 of 0.26 and 0.80 mg/mL (260 and 800 ppm), respectively. SEM images of eggs treated with WSMoL for 24 h revealed discontinuity of the exochorionic network and the absence of the exochorionic cells and their tubercles. After 48 and 72 h of incubation, strong deformation and degeneration of egg surfaces were observed. In MuBL and MuHL-treated eggs, the presence of lumps on the surface of the eggs, disappearance of the exochorionic network and the decrease and deformation of tubercles were observed. Lastly, fluorescence microscopy revealed that the three lectins were able to enter the eggs and reach the digestive tract of the embryos. CONCLUSION: WSMoL, MuBL, and MuHL are ovicidal agents on A. aegypti that have differing efficiencies in terms of how they cause alterations in the chorionic surface and in terms of their ability to penetrate the eggs. © 2019 Society of Chemical Industry.

Exposure of mosquito (Aedes aegypti) larvae to the water extract and lectin-rich fraction of Moringa oleifera seeds impairs their development and future fecundity.

Aedes aegypti control is a key component of the prophylaxis of dengue fever and other diseases. Moringa oleifera seeds contain a water-soluble lectin (WSMoL) with larvicidal and ovicidal activities against this insect. In this study, A. aegypti individuals were exposed at the third larval instar for 24 h to the water extract (0.1-1.0 mg/mL of protein) or lectin-rich fraction (0.05-0.6 mg/mL of protein) containing WSMoL, and then their survival and development were followed for 9 days post-exposure. The feeding capacity of adult females that developed from the treated larvae and the hatching success of eggs laid by them were also evaluated. Further, any alterations to the midgut histology of treated larvae, pupae, and adults were investigated. The extract and fraction induced the death of A. aegypti larvae along the post-exposure period. Both preparations also delayed the developmental cycle. The midguts of treated larvae and pupae showed disorganization and epithelial vacuolization, while in treated adults, the epithelium was underdeveloped compared to control. Unlike in control mosquitos, proliferating cells were not detected in treated larvae, and appeared in lower numbers in treated pupae than in control pupae. Adult females that developed from larvae treated with the fraction gained less weight after a blood meal compared with control. The amount of eggs laid by females that developed from larvae treated with both the extract and fraction was significantly lower than in control. In addition, the eggs showed lower hatching rates. In conclusion, females that developed from larvae treated with both the water extract and lectin-rich fraction showed reduced engorgement after a blood meal, with the consequent impairment of their fertility and fecundity. These results were probably due to the damage to midgut organization and impairment of the remodeling process during metamorphosis.