Stênio Nunes Alves

Susceptibility of Culex quinquefasciatus larvae to different insecticides

INTRODUCTION This study aimed to assess the susceptibility of Culex quinquefasciatus larvae to two pyrethroids (Cypermethrin and Deltamethrin), two derivatives of Avermectin (Ivermectin and Abamectin) and an organophosphate (Temephos). METHODS Third- and fourth-instar larvae of C. quinquefasciatus were exposed to different concentrations of insecticides (eleven repetitions) according to the World Health Organizations protocol. One hour after exposure, larvae were washed in dechlorinated tap water, transferred to plastic containers containing water without chlorine, fed and observed for periods of 24h until reaching adulthood. To determine lethal concentrations, the obtained values were submitted to regression analysis using the probit model with the Minitab 15 program. RESULTS The highest concentration used for the LC50 from probit analysis was for Temephos. The evaluated insecticides caused more pronounced larvae mortality in the first 24h with the exception of those exposed to ivermectin. CONCLUSIONS This study demonstrates that larvae are susceptible to all tested insecticides and that there is a need for monitoring the use of insecticides.

Dengue outbreaks in Divinopolis, south‐eastern Brazil and the geographic and climatic distribution of Aedes albopictus and Aedes aegypti in 2011–2012

To entomologically monitor Aedes spp. and correlate the presence of these vectors with the recent epidemic of dengue in Divinopolis, Minas Gerais State, Brazil.

Larvicidal activity of the methanol extract and fractions of the green fruits of Solanum lycocarpum(Solanaceae) against the vector Culex quinquefasciatus (Diptera: Culicidae)

INTRODUCTION The larvicidal activity of Solanum lycocarpum against Culex quinquefasciatus is unknown. METHODS We evaluated the larvicidal activity of extracts of the green fruits of Solanum lycocarpum against third and fourth instar larvae of C. quinquefasciatus. RESULTS Dichloromethane and ethyl acetate fractions showed the greatest larvicidal effect at 200mg/L (83.3% and 86.7%, respectively). The methanol and dichloromethane, ethyl acetate, and hydromethanolic fractions demonstrated larvicidal effects against C. quinquefasciatus, with LC50 values of 126.24, 75.13, 83.15, and 207.05 mg/L, respectively. CONCLUSIONS Thus, when considering new drugs with larvicidal activity from natural products, S. lycocarpum fruits may be good candidate sources.

Larvicidal activity of oils, fatty acids, and methyl esters from ripe and unripe fruit of Solanum lycocarpum (Solanaceae) against the vector Culex quinquefasciatus (Diptera: Culicidae)

INTRODUCTION The larvicidal activity of oils, fatty acids, and methyl esters of Solanum lycocarpum fruit against Culex quinquefasciatus is unknown. METHODS The larvicidal activity of samples of ripe and unripe fruit from S. lycocarpum was evaluated against third and fourth instar larvae of C. quinquefasciatus . RESULTS The oils, fatty acids, and methyl esters of S. lycocarpum showed the greatest larvicidal effect (57.1-95.0%) at a concentration of 100mg/L (LC 50values between 0.70 and 27.54mg/L). CONCLUSIONS Solanum lycocarpum fruit may be a good source of new natural products with larvicidal activity.

Larvicidal activity of vegetable oils and esterified compounds against Culex quinquefasciatus (Diptera: Culicidae)

Control of Culex quinquefasciatus using chemical insecticides may result in the selection of resistant mosquito strains. Thus, the use of plant-derived products has been studied as alternative for the mosquito control. Fatty acid methyl esters (FAMEs) obtained by transesterification of vegetable oils may result in compounds with larvicidal potential against C. quinquefasciatus. However, little is known about the morphological, physiological or biochemical effects that these FAMEs may have on mosquito larvae. The present study reports the effects of these FAMEs in mosquito larvae. The FAMEs were obtained by transesterification of canola, corn, sunflower, and soybean oils with acid catalysis and the determination of FAMEs composition was done by gas chromatography-mass spectrometry (GC-MS). Larvae of C. quinquefasciatus were exposed to different concentrations of the vegetable oils and FAMEs. Thereby, different FAMEs showed LC50 values ranging from 42.32 to 196.27mg/L against C. quinquefasciatus larvae. The methyl ester obtained from sunflower oil showed the lowest LC50. Histology of C. quinquefasciatus larvae exposed to LC50 of FAMEs was performed and changes in the midgut and fat body morphology were identified. Therefore, larval mortality and changes in the internal organs suggested that FAMEs might be a promising new class of larvicidalcompounds. Cytotoxicity of FAMEs compounds was assessed with the HeLa human cell line and no effect was observed.

Toxicity of different fatty acids and methyl esters on Culex quinquefasciatus larvae

The Culex quinquefasciatus mosquito is a vector of several diseases, and its control has been performed with synthetic insecticides, which may have human and environmental side effects. Thus, the use of new and safe molecules are important, and this study evaluated the toxicity of active substances against this mosquito. The oleic, linoleic, linolenic, palmitic and stearic acids and their respective methyl esters were tested against fourth instar C. quinquefasciatus larvae. Oleic, linoleic and linolenic acids had LC50 values of 8.58, 10.04 and 19.78 mg/L, respectively. Histological analysis showed that these three compounds caused cell instability with an increase in the number of vesicles in the fat body and in the midgut cells. Based on these results, glucose, triglyceride, and protein levels were evaluated after 1 h of acid exposure. These compounds decreased in insects treated with linoleic acid. Linolenic acid also caused a significant increase in acetylcholinesterase activity. These results show that oleic, linoleic, and linoleic acids have a lower LC50 for C. quinquefasciatus, affecting its metabolism and the morphology of midgut and fat body.

RESPONSE OF Culex quinquefasciatus LARVAE TO THREE INSECTICIDES

The adult females of Culex quinquefasciatus are vectors responsible for transmission of different arboviruses and lymphatic filariasis. The mosquito has anthropophilic and endophilics habits, their larvae develop in almost all habitats modified by humans. Different insecticides groups such as organophosphates, carbamates, and pyrethroids have been widely used in mosquito control, but in some places, the temephos has shown ineffectiveness for effective control of C. quinquefasciatus as a result of resistance development. So, there is a need of monitoring the populations through periodic studies for the detection of susceptibility.