Phytochemical characteristics of petroleum ether extracted seeds of the Indian almond, Terminalia catappa (L.) (Combretaceae) and the tamarind, Tamarindus indica (L.) (Fabaceae) for their larvicidal prospects against third instar larvae of Aedes aegypti, Aedes vittatus and Culex quinquefasciatus species of mosquito were evaluated under laboratory and simulated field conditions. Dried seeds of both trees were pulverised and extracted with petroleum ether (60 - 80°C) in a Soxhlet apparatus. Physicochemical characteristics of the seed oils were determined using standard protocols. Gas Chromatography - Mass Spectroscopy (GC-MS) was used to characterise the phytochemicals contained in the oils. Distilled water diluted extracts of the seeds at separate triplicate treatment concentrations of 0mL/L (control), 0.5mL/L, 1mL/L, 2mL/L, 4mL/L and 8mL/L were each tested on 25 triplicates (n=75) of each larval species for 24 hours under both conditions. Larval mortality was determined thereafter and the data was subjected to ANOVA to test for treatment based significant differences in mean larval mortality, and to determine species specific median lethal concentrations (LC50). Seed oils' acid values, percentage free fatty acids, peroxide values and refractive indices of 16.60mgKOH/g, 8.41mgKOH/g, 12.88meq/kg fat and 1.48 respectively in T. indica were significantly (p < 0.05) higher than the 10.66mgKOH/g, 5.33mgKOH/g, 9.27meq/kg fat and 1.46 respectively in T. catappa. However, the iodine value (39.35meq/kg fat) of T. catappa seed oil was significantly (p < 0.05) higher than the 16.18meq/kg fat value of T indica seed oil. There was no significant (p > 0.05) difference between the saponification values of 162.75mL/kg and 187.94mL/kg for T. catappa and T. indica seed oils respectively. Sixteen metabolites of mainly saturated and unsaturated fatty acids including pentadecanoic acid (8.57%), linolelaidic acid (15.30%), elaidic acid (9.15%), stearic acid (5.09%), ricinoleic acid (1.52%), eicosenoic acid (2.83%), eicosanoic acid (2.82%) and heneicosanoic acid (8.77%) were detected in the seed oil of T. indica. Fourteen metabolites of mainly saturated and unsaturated fatty acids including hexadecanoic (palmitic) acid (13.36%), linolelaidic acid (9.97%), oleic acid (11.02%), stearic acid (5.83%) and eicosanoic (arachidic) acid (0.66%) were detected in the seed oil of T. catappa. Terminalia. catappa seed oil caused significantly (p < 0.05) highest larval Ae. aegypti mortality of 81% and 55% and LC50 values of 4.840mL/L and 10.884mL/L; highest larval Ae. vittatus mortality of 53% and 45% and LC50 of 11.143mL/L and 9.099mL/L; highest larval Cx. quinquefasciatus mortality of 91% and 80% and LC50 of 2.275mL/L and 3.055mL/L, under laboratory and simulated field conditions respectively.
Tamarindus indica seed oil caused significantly (p < 0.05) highest larval Ae. aegypti mortality of 99% and 95% and LC50 values of 1.248mL/L and 1.359mL/L; highest larval Ae. vittatus mortality of 60% and 76% and LC50 of 4.842mL/L and 1.191mL/L; highest larval Cx. quinquefasciatus mortality of 95% and 100% and LC50 of 0.690mL/L and 0.625mL/L, under laboratory and simulated field conditions respectively. Tamarindus. indica extract was a better larvicidal agent against the three mosquito species than T. catappa. Seed extracts of both trees could thus be adopted in mosquito control operations.
1.1 Background of the Study
Mosquitoes are the most important single group of insects well-known for their public health importance. Since they act as vectors for many tropical and subtropical diseases, they cause nuisance by their bites and also transmit deadly diseases like malaria, filariasis, yellow fever, dengue and Japanese encephalitis, which contribute significantly to poverty and social debility in tropical countries (Jang et al., 2002; Tiwary et al., 2007). They can transmit more diseases than any group of arthropods and affect millions of people throughout the world. World Health Organization (WHO) has declared mosquitoes as “public enemy number one” (WHO, 1996).
Aedes species are important vectors of yellow fever, dengue, encephalitis viruses and many other arboviruses, and in a few restricted areas they are also vectors of Wuchereria bancrofti and Brugia malayi, (Kandaswamy et al., 2012). Aedes aegypti is the primary vector of dengue and chikungunya. Aedes vitattus is a vector of chikungunya and yellow fever (Misvar et al., 2014).
Culex quinquefasciatus (Say), commonly known as the southern house mosquito is a medium-sized brown mosquito that exists throughout the tropics and the lower latitudes of temperate regions. Culex quinquefasciatus is the primary vector of St. Louis encephalitis virus and also transmits West Nile virus (Hill and Connelly, 2013). Despite progress in vaccine development, no effective and acceptable multivalent vaccines are currently available against mosquito-borne diseases (Klempner et al., 2007).....