This study describes morphological alterations in the fat body and midgut of Culex quinquefasciatus larvae following exposure to different insecticides. To this end, both third and fourth instars of C. quinquefasciatus larvae were exposed for 30 and 60 min to organophosphate (50 ppb), pyrethroids (20 and 30 ppb), and avermectin derivates (1.5 and 54 ppb). Following incubation, pH measurements of the larvae gut were recorded. The fat body and midgut were also analyzed by light and transmission electron microscopy. These studies demonstrate a decrease in the pH of the larvae anterior midgut following exposure to all of the tested insecticides. Histochemical tests revealed a strong reaction for neutral lipids in the control group and a marked decrease in the group exposed to cypermethrin. Furthermore, a weak reaction with acidic lipids in larvae exposed to deltamethrin, temephos, ivermectin and abamectin was also observed. Insecticide-exposed larvae also exhibited cytoplasm granule differences, relative to control larvae. Finally, we noted a small reduction in microvilli size in the apex of digestive cells, although vesicles were found to be present. The destructive changes in the larvae were very similar regardless of the type of insecticide analyzed. These data suggest that alterations in the fat body and midgut are a common response to cellular intoxication.

ABSTRACT

The effects of ivermectin, a semi-synthetic drug widely used for treatment of livestock parasite diseases, were observed on Culex quinquefasciatus larvae. Toxic effects and mortality evaluation were carried out after 5, 15, 30 and 60 minutes of exposure to 1, 5 or 10 ppm of ivermectin solutions. Observations were made 24 and 48 hours after the beginning of the experiment, and loss of mobility, progressive paralysis and high mortality of larvae were recorded. The observed effects of ivermectin on the mosquito larvae is probably correlated with chloride channel activation on cell membranes.

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.

The control of mosquitoes by means of chemical insecticides has been a problem, mainly due to the possibility of resistance developed by insects to xenobiotics. For this reason, demand for botanical insecticides has increased. In this sense, the present work aims to verify the susceptibility and morphological and biochemical alterations of Culex quinquefasciatus larvae after exposure to essential oil (EO) of leaves of Baccharis dracunculifolia. To observe the larvicidal action, larvae were exposed to EO at concentrations of 25, 50, 100, and 200 mg/L, until their emergence to adults. The control group was exposed to deionized water and dimethyl sulfoxide. Morphological analyses were also carried out using hematoxylin and eosin, mercury bromophenol blue, Nile blue, and periodic acid Schiff. Biochemical analyses of total glucose, triacylglyceride (TAG), protein, and acetylcholinesterase levels were performed. The phytochemical analysis of the EO showed (E)-nerolidol as the major compound (30.62%). Larvae susceptibility results showed a LC of 34.45 mg/L for EO. Morphological analysis showed that there were histological changes in midgut. For biochemical analyses, the glucose level in the larvae exposed to EO for 24 h decreased significantly, unlike the TAG levels, which increased. The total protein level of the larvae also increased after exposure for 24 h, and acetylcholinesterase levels decreased significantly. Taking all our data into account, we can conclude that EO causes destabilization in larva, leading to histological changes, metabolic deregulation and, consequently, their death.

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 50 values between 0.70 and 27.54mg/L). Conclusions: Solanum lycocarpum fruit may be a good source of new natural products with larvicidal activity.Keywords: Bioassay. Mosquito. Pesticide. Synthetic insecticides are used to control mosquito vectors of diseases in several parts of the world. However, resistance to synthetic insecticides has recently become problematic in vector control programs. Thus is important the development of new products, with the capacity to prevent or minimize the resistance, to combat insects (1) . Biological products represent alternative approaches for preventing the development of resistance in mosquitoes.Plants contain bioactive compounds with insecticidal properties that could be suitable for mosquito control applications (2) . Several species of the genus Solanum have demonstrated larvicidal and pupicidal activities against the mosquito Culex quinquefasciatus (3) (4) (5) . Solanum lycocarpum A. St. Hil. (Solanaceae) is popularly known as the fruit of the wolf and is widely distributed in the Brazilian Cerrado (6) . Solanum lycocarpum is commonly used in traditional medicine as a sedative and a treatment for epilepsy, asthma, diabetes, obesity, abdominal pain, renal pain, and high cholesterol levels (7) . Despite the widespread medicinal usage of S. lycocarpum and the reported insecticidal properties of other Solanum species, no studies have been conducted on the insecticidal activity of oils, fatty acids, and methyl esters obtained from the ripe and unripe fruit of S. lycocarpum.Fruit of S. lycocarpum A. St. Hil. were collected in São Sebastião do Oeste, Minas Gerais, Brazil in August 2011. The plant material was identifi ed by Dr. Alexandre Salino. A voucher specimen (BHCB 159397) was deposited at the Instituto de Ciências Biológicas Herbarium, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil. Samples of the dried and powdered unripe (170.01g) and ripe (250.58g) fruit were subjected to oil extraction using a Soxhlet extractor with petroleum ether as the solvent (Vetec®, São Paulo, Brazil; 700mL, 6h). The extracted oils were concentrated in a rotary evaporator at 50°C under reduced pressure to produce 26.95g of oil of unripe fruit (OUF) and 29.09g of oil of ripe fruit (ORF).Fatty acids and methyl esters were isolated from S. lycocarpum via transesterifi cation (8) . OUF and ORF (2g each) were refl uxed with 1.0 mol/L methanolic NaOH solution for 30 min and extracted with ethyl ether. The aqueous phases were acidifi ed with 1.0 mol/L HCl solution and extracted with ethyl ether to obtain fatty...

Culex quinquefasciatus (Say, 1823), known as the domestic mosquito, is a common and abundant species throughout the world, and a cosmopolitan species. The adults of this mosquito are important in terms of public and animal health since they display adaptability to different hosts. In humans, they are responsible for the transmission of various diseases. One manner of control of this vector is the use of insecticidal or larvicidal products, which may have the drawback of toxicity to mammals and can be harmful to the environment. The present work evaluated the larvicidal potential of the essential oil (EO) and ascaridole-enriched fraction (EF4-5) obtained from the leaves of Peumus boldus Molina (boldo). The EO, obtained by steam distillation, was analyzed by GC/MS and fractionated on silica gel. EO and EF4-5, containing 31.4% and 89.5% ascaridole, respectively, were evaluated against C. quinquefasciatus at concentrations of 100, 50 and 25 μg/ml on the third and fourth instars. They showed lethal concentrations (LC) of 82.14 and 41.85 μg/ml, respectively. Larvae treated with the EF4-5 showed morphological changes in the midgut, with cells possessing a cytoplasm that contained small vacuole-like structures, as well as a nucleus with decondensed chromatin and a cell apex with a short brush border. The cells of the fat body showed larger protein granules, which were acidophilic relative to the larvae of the control group. Moreover, the enriched fraction at a dose of 50 μg/ml showed a residual larvicidal effect according to exposure time on C. quinquefasciatus. This residual effect deserves consideration, since a long-term larvicidal product may be a useful tool for vector control.

The species Culex quinquefasciatus (Diptera: Culicidae) is a mosquito inhabiting urban regions, with a wide geographical distribution. This species is involved in the transmission of lymphatic fi lariasis in the Americas, particularly in Brazil. C. quinquefasciatus is of great importance in public health as it creates administrative and public challenges for the control of mosquito vectors 1 . Synthetic insecticides have been widely used to control mosquito vectors of disease in various parts of the world; however, resistance to these insecticides has recently become problematic in vector control programs. Moreover, the continuous monitoring of mosquito populations may play an important role in attempting to develop management strategies that will prevent or minimize the development of resistance to pesticides, as well as to develop new products to combat insects 2 . Thus, the use of biological products is an alternative approach for preventing the development of resistance in mosquitoes.Plants are a source of bioactive compounds that have insecticidal properties and therefore may be suitable for mosquito control 3 . Phytoextracts have previously been shown to be successful in various biocontrol programs, and essential The species Solanum lycocarpum A. St. Hil., belonging to the Solanaceae family, is popularly known as lobeira and is widely distributed in the Brazilian cerrado 6 . It is widely used in traditional medicine as a sedative, in the treatment of epilepsy, asthma, diabetes, obesity, for the reduction of cholesterol levels, and for abdominal and renal pain 7 .To our knowledge, for the fi rst time, we show the larvicidal activities of the extracts and fractions obtained from the green fruits of S. lycocarpum against C. quinquefasciatus.The green fruits of S. lycocarpum A. St. Hil. were collected in the City of São Sebastião do Oeste, State of Minas Gerais, Brazil, in August 2011. The plant material was identifi ed by Dr. Alexandre Salino, and a voucher specimen (BHCB 159397) was deposited at the Instituto de Ciências Biológicas Herbarium, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil. Methanol was used as solvent to obtain the extract from 170.01g of dried and powdered green fruits, using a Soxhlet extractor. The extract was then concentrated in a rotary evaporator at 50°C under reduced pressure to yield the methanol extract (MET, 14.53g). Some of this extract (6.82g) was dissolved in MeOH/H 2 O (1:1) and then partitioned successively with hexane, dichloromethane, and ethyl acetate (Vetec®, São Paulo, Brazil; 100 mL, twice with each solvent), yielding 0.09, 0.23, 0.34, and 5.50g of hexane (HEX), dichloromethane (DCM), ethyl acetate (AC), and hydromethanolic (HM) fractions, respectively. The extract and fractions were screened for the presence of different phytoconstituents such as saponins, tannins, alkaloids, steroids, triterpenes, coumarins, and fl avonoids Culex quinquefasciatus larvae were obtained from a laboratory culture, as previously described by Gerberg 9 . Both the third and...