Laboratory observations on the larvicidal efficacy of three plant species against mosquito vectors of malaria, Dengue/Dengue Hemorrhagic Fever (DF/DHF) and lymphatic filariasis in the semi-arid desert.

Comparative larvicidal efficacy of aqueous and organic solvent extracts from seeds, leaves and flowers of three desert plants viz. Calotropis procera (Aiton), Tephrosia purpurea (L.) Pers. and Prosopis juliflora (Sw.) DC. was evaluated against Anopheles stephensi (Liston), Aedes aegypti (Linnaeus) and Culex quinquefasciatus (Say). For this purpose larvae of all the three mosquito species were reared in the laboratory and studies carried out on late 3rd or early 4th instars using standard WHO technique. Based on concentration mortality data 24 and 48 hr LC50 and LC90 values along with their 95% fiducial limits, regression equation, chi-square (c2)/ heterogeneity of the response were determined by log probit regression analysis. Experiments were carried out with different solvent extracts of seeds of C. procera which revealed that methanol (24 hr LC50: 127.2, 194.8, 361.0) and acetone (229.9, 368.1, 193.0 mg l-1) extracts were more effective with the three mosquito species, respectively. Petroleum ether extract was effective only on An. stephensi while aqueous extracts were not effective at all with any of the mosquito species (mortality <10-30%). Tests carried out with methanol extracts of fresh leaves (24 hr LC50: 89.2, 171.2, 369.7) and flowers (24 hr LC50: 94.7,617.3, 1384.0 mg l-1) of Calotropis showed that preparations from fresh parts were 2-3 times more effective as compared to the stored plant parts. Efficacy was less than 10-30% with both An. aegypti and Cx. quinquefasciatus while An. stephensi was still susceptible to extracts from both leaves and flowers even after two years of storage. The 24 hr LC50 values as observed for methanol extracts of seeds of T. purpurea and leaves of P. juliflora were 74.9, 63.2 and 47.0 and 96.2, 128.1 and 118.8 mg l-1 for the above three mosquito species, respectively. Experiments carried out up to 500 mg l-1 with leaves (T. purpurea) and seeds (P. juliflora) extracts show only up to 10-30% mortality indicating that active larvicidal principle may be present only in the seeds of Tephrosia and leaves of Prosopis. In general, anophelines were found more susceptible than the culicines to the plant derived derivatives. More studies are being carried out on some other desert plants found in this arid region. The study would be of great importance while formulating vector control strategy based on alternative plant based insecticides in this semi-arid region.

Comparative larvicidal potential of different plant parts of Withania somnifera against vector mosquitoes in the semi-arid region of Rajasthan.

Larvicidal potential of the extracts from different parts viz. green and red fruits, seeds, fruit without seeds, leaves and roots of Withania somnifera in different solvents was evaluated against larvae of Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus, the important disease vectors prevalent in the semi-arid region. Experiments were carried out on late 3rd or early 4th instar larvae of these mosquitoes using standard WHO technique. 24 and 48 hr LC 50 values along with their 95% confidence limits, regression equation, chi-square (c2)/ heterogeneity of the response have been determined by log probit regression analysis. The 24 hr LC50 values as observed for whole green fruits in water, methanol and petroleum ether were 350.9, 372.4, 576.9; 115.0, 197.1, 554.6; 154.9, 312.0, 1085.0 while corresponding values for red fruits were 473.5, 406.4, 445.2; 94.7, 94.5, 1013.0; 241.8, 535.0, 893.3 mg l-1 for An. stephensi, Ae. aegypti and Cx. quinquefasciatus respectively showing that methanol extracts were more effective against anophelines as compared to culicines when whole fruits were taken. The 24 hr LC50 values as observed for seeds in acetone, methanol and petroleum ether were 188.1, 777.5, 822.5; 245.5, 769.0, 1169.0; 140.3, 822.9, 778.4 and for fruit without seeds were 80.2, 97.6, 146.6; 88.4, 404.4, 1030.0; 30.0, 44.5, 54.2 mg l-1 for the above mosquito species respectively showing that extract of fruit without seeds were most effective in petroleum ether followed by acetone and methanol extracts. However, experiments conducted with methanol extracts of leaves and roots of this plant species did not show any appreciable larvicidal activity and a 20-40% mortality was observed up to 500 mg l-1 of the extracts. Overall larvae of anophelines were found more susceptible as compared to culicines to all the extracts tested. Petroleum ether extract of fruit without seeds was found most effective against all the mosquito species showing that active ingredient might be present in this part of the plant species. The study would be of great importance while planning vector control strategy based on alternative plant derived insecticides.

Evaluation of larvicidal efficacy of Solanum xanthocarpum storage against vector mosquitoes in north - western Rajasthan.

Efficacy of the methanol extracts from fruits without seeds, whole yellow ripe fruits and seeds of the plant Solanum xanthocarpum was evaluated against larvae of Anopheles culicifacies, Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus, the important vector mosquitoes prevalent in the arid region. Experiments were carried out on late 3rd or early 4th instar larvae of these mosquitoes using standard WHO technique. 24 and 48 hr LC50 and LC90 values along with their fiducial limits, regression equation, chi-square (x2)/ heterogeneity of the response have been determined by log probit regression analysis. The 24 hr LC50 values as observed for fruit without seeds, whole fruits and seeds after six months were 79.6, 91.7 and 131.7; 131.4, 186.9 and 195.6; 273.4, 290.9 and 377.6 and 384.9, 450.6 and 520.0 mgl-1 for An. culicifacies, An. stephensi, Ae. aegypti and Cx. quinquefasciatus respectively. However, the 24 hr LC50 values for fresh yellow ripe fruits and seeds determined previously were 51.6 and 66.9; 52.2 and 73.7; 118.3 and 123.8 and 157.1 and 154.9 mgl-1 for the above four vector species respectively showing that the efficacy was decreased two to three times more after six months of storage. The 24 hr LC50 values were also determined after one year of storage for fruit without seeds, whole fruits and seeds. The values were 103.3, 120.1 and 195.7; 146.3, 224.3 and 251.2; 316.9, 336.5 and 426.2 and 393.0, 500.3 and 656.7 mgl-1 as compared to the 24 hr LC50 values of 47.4,51.6 and 66.9; 52.3,52.2 and 73.7; 108.0,118.3 and 123.8 and 141.1, 157.1 and 154.9 mgl-1 of all the three fresh preparations for the above four vector species respectively showing that the efficacy was further decreased after one year of storage. Further the extracts should be used when they have been prepared from the fresh plant parts instead of the old stored parts. Larvae of anophelines were found more susceptible as compared to culicine. HPLC and IR studies showed that active component might be present in the fruits and seeds of this plant species. The study would be of great importance while planning vector control strategy based on alternative plant derived insecticides.

Larvicidal activity of the extracts from different parts of the plant Solanum xanthocarpum against important mosquito vectors in the arid region.

Larvicidal efficacy of the aqueous and methanol extracts from green unripe and yellow ripe fruits, seeds, leaves and roots of the plant Solanum xanthocarpum was evaluated against Anopheles culicifacies, Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus, the important mosquito vectors prevalent in the arid region. Studies were carried out on late 3rd or early 4th instar larvae of these species using standard WHO technique. Based on concentration mortality data LC50 and LC90 values along with their fiducial limits, regression equation, chisquare (l2)/ heterogeneity of the response have been determined by log probit regression analysis. The 24 hr LC50 values as observed for aqueous extracts for green unripe and yellow ripe fruits were 112.7, 498.2 and 846.3 mgl-1 and 104.7, 267.7 and 832.2 mg l-1 for Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus respectively. However, the 24 hr LC50 values for methanol extracts of yellow ripe fruits and seeds were 51.6, 52.2, 118.3 and 157.1 mg l-1 and 66.9, 73.7, 123.8 and 154.9 mg l-1 for the above four vector species respectively. The results showed that larvae of anophelines were much more susceptible as compared to culicines to both the aqueous and methanol extracts from fruits and seeds of the plant tested. The methanol extracts were found 2-5 times more effective as compared to the aqueous extracts. The chi-square values calculated during the analysis did not show any heterogeneity of the response. Experiments conducted with aqueous and methanol extracts from leaves and roots of this plant species didn’t show any larvicidal activity against any of the mosquito species tested. The study would be of great importance while formulating vector control strategy based on alternative plant based insecticides.

Relative susceptibility of some common mosquito vector larvae to synthetic insecticidal compounds in north-western Rajasthan.

Relative susceptibility of three important mosquito vector larvae viz., Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus, prevalent in the arid region was determined against four organophosphates (malathion, fenitrothion, fenthion, temephos) and three synthetic pyrethroid (alphamethrin, deltamethrin and fanvalerate) compounds. Studies were carried out on late 3rd or early 4th instar larvae of these species using standard WHO technique. Based on concentration mortality data LC50 and LC90 values along with their fiducial limits, regression equation, chi-square (chi2)/heterogeneity of the response have been determined by log probit regression analysis. LC50 values as observed for the above seven insecticides were 0.8097, 0.0398. 0.0432, 0.0035, 0.0025, 0.0092, 0.1006; 1.2370, 0.0531, 0.0655, 0.0076, 0.00004, 0.00004, 0.0046 and 1.4980, 0.0719, 0.0817, 0.0056, 0.00021, 0.00073, 0.0112 mg/l for the above three mosquito species respectively Among the four organophosphates tested temephos was the most effective followed by fenitrothion, fenthion and malathion. In general, Anopheles was found more susceptible as compared to the other two culicines to the above four compounds. The results also showed that larvae of Ae. aegypti were most susceptible followed by Cx. quinquefasciatus and An. stephensi to all the three pyrethroids tested. Among the three compounds tested alphamethrin was found to be the most toxic followed by deltamethrin while fanvalerate was the least toxic. The study would be of great importance while planning use of these insecticides for the control of different vector species in this area.

Efficacy of different organophosphate and synthetic pyrethroid insecticides to the larvae of malaria vector Anopheles stephensi, Liston.

Evaluation of the potency of four organophosphate (OP) (Malathion, Fenthion, Fenitrothion and Temephos) and two synthetic pyrethroid (SP) compounds (cypermethrin and deltamethrin) was carried out against larvae of Anopheles stephensi, the major malaria vector in district Bikaner (Rajasthan). Different concentrations supplied by WHO were used for determining the percent mortalities. LC50 values as calculated by probit analysis were 1.2740, 0.0600, 0.0405, 0.0046, 0.0019 and 0.0016 mg/l respectively for the above six insecticides. Both SP compounds were found more toxic followed by temephos among the OP compounds. Malathion was found the least toxic while fenthion and fenitrothion were in between these two extremes.

Insecticide susceptibility status of Aedes aegypti to DDT and dieldrin in desert and non-desert parts of Rajasthan.

Seasonal prevalence and insecticide susceptibility tests were carried out on the adults of Aedes aegypti, the vector of dengue and dengue hemorrhagic fever(DF/DHF), in three desert (Bikaner, Jaisalmer and Jodhpur) and three non-desert (Alwar, Ajmer and Jaipur) districts of Rajasthan. Among the three species viz. Ae. aegypti, Ae. vittatus and Ae. w-albus encountered during the survey the former was the most prevalent species. Studies were carried out both in rural and urban areas against different concentrations of two organochlorines (DDT and Dieldrin). In rural areas resistance has been observed with DDT and dieldrin both in desert and non-desert parts while an intermediate resistance has been observed in the urban areas with both the insecticides which required further verification. Resistance was more pronounced in rural areas as compared to urban areas. LC50 along with regression equation and Chi-square values have been determined for both the insecticides.