Bioactivity of plant extracts on the larval and pupal stages of Aedes aegypti (Diptera, Culicidea)

Introduction Aedes aegypti is responsible for the transmission of the dengue and yellow fever viruses. This study evaluated the effects of extracts from Cnidosculos phyllacanthus, Ricinus communis, and Coutarea hexandra on the developmental periods of A.aegypti larvae and pupae. Crude extracts of C. phyllacanthus and C. hexandra and oil from R. communis and C. phyllacanthus were used. Methods Bioassays of the larvicidal and pupicidal effects of these products at different concentrations and times of exposure were evaluated. The lethal and sublethal effects were determined using different concentrations in larvicidal tests. Mortality data were evaluated by Probit analysis to determine the LC50 and LC90 values. Results The vegetable oils from C. phyllacanthus and R. communis demonstrated greater efficiency for larval control with an LC50=0.28µl/mL and an LC90=1.48µl/mL and LC50=0.029µl/mL and a LC90=0.26µl/mL, respectively. In pupal tests toxic effects for all insects were verified after exposure to the products at significant LC50 and LC90 values for 24 and 48h. The effects of sublethal concentrations of C. phyllacanthus (oil) were more effective on the insects. Conclusions The vegetables oils from C. phyllacanthus and R. communis demonstrated greater potential from the control of different developmental periods in the life cycle of this insect. .

Molluscicidal and Mosquitocidal Activities of the Essential oils of Thymus capitatus Hoff. et Link. and Marrubium vulgare L. / Atividades moluscicida e mosquitocida de óleos essenciais de Thymus capitatus Hoff. et Link. e de Marrubium vulgare L

Steam distillation of essential oils of aerial parts of Thymus capitatus and Marrubium vulgare L. collected at North cost of Egypt yielded 0.5% and 0.2%, respectively. Results of Gas chromatography-mass spectrometry analyses of the two samples identified 96.27% and 90.19% of the total oil composition for T. capitatus and M. vulgare, respectively. The two oil samples appeared dominated by the oxygenated constituents (88.22% for T. capitatus and 57.50% for M. vulgare), composed of phenols, mainly carvacrol (32.98%) and thymol (32.82%) in essential oil of T. capitatus, and thymol (34.55%) in essential oil of M. vulgare. It was evaluated the molluscicidal activity of T. capitatus and M. vulgare essential oils on adult and eggs of Biomphalaria alexandrina as well as their mosquitocidal activity on Culex pipiens. The LC50 and LC90 of T. capitatus essential oil against adult snails was 200 and 400 ppm/3hrs, respectively, while for M. vulgare it was 50 and 100 ppm/3hrs, respectively. Moreover, M. vulgare showed LC100 ovicidal activity at 200 ppm/24 hrs while T. capitatus oil showed no ovicidal activity. It was verified mosquitocidal activity, with LC50 and LC90 of 100 and 200 ppm/12hrs respectively for larvae, and 200 and 400 ppm/12hrs respectively for pupae of C. pipiens.

A destilação por arraste a vapor dos óleos essenciais de partes aéreas de Thymus capitatus Hoff. et Link. e de Marrubium vulgare L. coletadas na costa norte do Egito resultaram em rendimento de 0,5% e 0,2%, respectivamente. Resultados de análises por cromatografia gasosa acoplada à espectrometria de massas de ambas as amostras possibilitaram a identificação de 96,27% e 90,19% dos constituintes químicos respectivamente de T. capitatus e M. vulgare. Verificou-se predomínio de constituintes oxigenados (88,22% para T. capitatus e 57,50% para M. vulgare, principalmente fenóis, como carvacrol (32,98%) e timol (32,82%) no óleo essencial de T. capitatus, e timol (34,55%) no óleo essencial de M. vulgare. Avaliou-se a atividade dos óleos essenciais obtidos contra adultos e ovos de Biomphalaria alexandrina, bem como em larvas e pupas de Culex pipiens. A CL50 e CL90 do óleo essencial de T. capitatus em moluscos adultos foi respectivamente 200 e 400 ppm/3hrs, enquanto para o óles essencial de M. vulgare verificou-se CL50 e CL90 de 50 e 100 ppm/3hrs, respectivamente. Além disso, M. vulgare apresentou atividade ovicida, com CL 100 de 200 ppm/24 horas, enquanto o óleo essencial de T. capitatus não demonstrou atividade ovicida. Verificou-se ainda atividade mosquitocida, com CL50 e CL90 de 100 e 200 ppm/12hrs respectivamente para larvas, e 200 e 400 ppm/12hrs contra pupas de C. pipiens.

Efficacy of pirimiphos-methyl (50% EC), as a larvicide for the control of Culex quinquefasciatus.

Background & objectives: Pirimiphos-methyl, an organophosphorus insecticide is known to overcome resistance mechanisms of mosquitoes to other organophosphates. Information on the duration of efficacy of pirimiphos-methyl (50% emulsifiable concentrate) for the control of immatures of Culex quinquefasciatus, the vector of bancroftian filariasis, is scanty and hence site specific field trials are necessary to determine the field dosage. Pirimiphos-methyl (50% EC) was tested for its efficacy in cesspits and drains against the immatures of Cx. quinquefasciatus at Puducherry, an endemic area for filariasis, south India. Methods: In cesspits, Pirimiphos-methyl (50% EC) was tested at the dosage of 25, 50, 100 and 200 g(ai)/ ha and in drains at 50, 100 and 200 g(ai)/ha. Immature density during pre-treatment and post-treatment periods was recorded and the efficacy was determined by calculating percentage reduction in larval and pupal densities for a period of about one month. Results: In cesspits, application of the insecticide at 25 and 50 g(ai)/ha reduced the density of larvae by >80 per cent for 2-4 days only, whereas at 100 and 200 g(ai)/ha, the efficacy lasted for 7-8 days. More than 80 per cent reduction was observed in pupal density for 4 days at 50 g(ai)/ha and for 10-12 days at 100 and 200 g(ai)/ha respectively. In drains treated with 50 g (ai)/ha, >80 per cent reduction in larval density was recorded up to 3rd day post-treatment. The efficacy showing >80 per cent reduction in larval density lasted for 12-13 days and the same in pupal density lasted for 10-12 days at 100 and 200 g(ai)/ha. Interpretation & conclusions: At the dosages of 100 and 200 g(ai)/ha, pirimiphos-methyl (50% EC) showed no difference in the control of larvae of Cx. quinquefasciatus in cesspits and drains. Pirimiphosmethyl may be applied at the field dosage of 100 g (ai)/ha at 10 day-intervals in the larval habitats of Cx. quinquefasciatus to achieve >80 per cent reduction in immature density.

Efficacy of agnique (mmf) monomolecular surface film against immature stages of Anopheles arabiensis patton and Culex spp (diptera: culicidae) in Khartoum, Sudan.

The efficacy of the larvicidal and pupicidal agent (Agnique) MMF was evaluated against larvae of An. arabiensis and Culex (Diptera: Culicidae) under field conditions in Bahary Locality, Khartoum, Sudan. At an applied dosage of 0.25 ml/m2, MMF resulted in 89.4, 79.8 and 88.2% reductions in L3-L4 instars An. arabiensis and 63.5% in Culex larvae (all stages) 24 to 72 hours post-treatment. Pupae were completely eliminated (100%) within 24 hours posttreatment. The earlier instars (L1-L2) of An. arabiensis were more tolerant with a 62.5% reduction at 72 hours post-treatment compared to (L3-L4) instars and pupae. At 7-days post-treatment Agnique gave a 57.5% reduction in L1-L2 and 92.6% in L3-L4 instar larvae of An. arabiensis and 57.3% and 86.4% in Culex larvae and pupae, respectively. We conclude that Agnique can perform effectively against L3-L4 instars and pupae of An. arabiensis for only 1 week, and 3 to 4 days against L1-L2 instars of Culex spp.

Efficacy of Bacillus thuringiensis israelensis, VectoBac WG and DT, formulations against dengue mosquito vectors in cement potable water jars in Cambodia.

This study reports the evaluation of Bacillus thuringiensis israelensis (Bti), a biological larvicide, in cement jars holding river, well and rain water. Two Bti formulations, VectoBac WG and VectoBac DT, were evaluated in a village in Phnom Penh. Thirty-one households with cement jars supporting the colonization of Ae.aegypti immatures were chosen. In each house 3 jars were aligned next to each another and filled with the same type of water. One of the 3 jars was treated with VectoBac WG at 0.4 g per 50 liters, a second jar was treated with VectoBac DT at 1 tablet per 50 liters, and a third jar was an untreated control (UTC). The jars were not covered, kept outdoors and not subjected to water exchange activity. The efficacy of VectoBac to control natural Ae.aegypti infestation was measured by Ae.aegypti pupae surveillance, conducted 3 days per week for 3 months post-treatment (June-September 2004). All pupae were removed, allowed to emerge in the Cambodia National Malaria Center insectarium and the emerged adults were identified and counted. The VectoBac treatments were more effective in river water, followed by well and rain water. The VectoBac treatments significantly reduced the pupae numbers for a minimum of 3 months in the river water and 2.5 months in the well water (p < 0.05). In the rain water, the pupae densities in the VectoBac WG and DT treated jars were not significantly different from the untreated jars, although the treated jars yielded 2.0 to 5.2 fold less pupae, respectively, than in the untreated jars during the 3 months post-treatment. The efficacy of VectoBac WG to control Ae.aegypti was similar to the efficacy of VectoBac DT in the 3 water types (p > 0.05). It was also observed that VectoBac WG and DT were target specific, without any adverse effects on aquatic predatory insects common in well and rain water. VectoBac WG and DT were found to be easy-to-use formulations, with no need to repackage them prior to use in the containers. The amounts of VectoBac WG and DT used were 12.5 fold less by weight than temephos (Abate 1.0% SG).

Three indigenous Thai medicinal plants for control of Aedes aegypti and Culex quinquefasciatus.

The potential larvicidal activity and insect growth regulator (IGR) properties of three selected indigenous medicinal Thai plants were tested against two species of mosquito with special reference to the late 3rd and early 4th instar larvae (L3 and L4, respectively). In case of larvicidal activity, Thevetia peruviana was the most potent, followed by Pueraria mirifica, and Butea superba was the least effective. In all cases, the late 3rd instar was more susceptible than the early 4th instar larvae, and the 48-hours exposure yielded more potent larvicidal activity than 24-hours exposure. However, at sublethal dosages, both P. mirifica and B. superba showed some dispersed effects interfering with ecdysis. A variety of toxic effects were observed and recorded in eight categories according to the stage of metamorphosis when death occurred. P. mirifica rendered the main deleterious effects in the pupa-adult period in both instar of Ae. aegypti and Cx. quinquefasciatus, whereas B. superba showed highest effect in black-pupa period of the late 3rd instar larval stage. The results were reversed for the early 4th instar larvae of both species of mosquito as the main effect appeared in the pupa-adult category. The overall results indicated that T. peruviana did not show any IGR properties; whereas, P. mirifica and B. superba seemed to exhibit the juvenile hormone type activity which resulted in abnormal death at various stages of development. B. superba was more promising than P. mirifica, and Ae. aegypti was about 2 times more susceptible than Cx. quinquefasciatus. In addition, L3 was always more susceptible than L4 with both mosquito species.

Effects of beta-cyfluthrin on white and sepia mutants of Drosophila melanogaster.

The effects of sublethal concentrations of a synthetic pyrethroid, beta-cyfluthrin (Bulldock 025 SC) were investigated in the F1 generations of white and sepia mutants of Drosophila melanogaster after various cross combinations of the parents which were exposed separately to the insecticide mixed diet for 24 hours. The experiment was carried out under the laboratory conditions at a temperature of 25+/-5 degrees C and 60+/-5% relative humidity. The insecticide had deleterious effect on the growth and development of both the mutant flies. Larval, pupal and total developmental periods were found to be increased as compared to controls, whereas the number of adult emerged decreased in all the treatment sets. Larval period index (LPI), pupal period index (PPI) and growth index (GI) were observed to be decreased in the entire cross combinations. Maximum effects were observed in those sets where both the sexes were treated, crossed and F1 generation was studied on the treated food having sublethal concentration of the insecticide, followed by similar treatment sets but on the fresh untreated food. Females were found to be resistant as compared to the males, whereas white mutant files were more susceptible to the test insecticide beta-cyfluthrin as compared to sepia mutant flies.

Plasmodium falciparum infection in Bisazir chemosterilized Anopheles dirus in laboratory studies.

Bisazir, at a 0.5% solution induced sterility in males and at a 1.5% solution in female A. dirus. These sterilizing doses reduced P. falciparum infection in mosquitoes, however, they can still transmit malaria. It is concluded that by the concentration of 1.5 and 2.0% that induced complete sterility in males and females are not safe in sterile-male release programme for the control of A. dirus, unless all females were eliminated prior to release.