A review of botanical phytochemicals with mosquitocidal potential.

Botanical insecticides are relatively safe and degradable, and are readily available sources of biopesticides The most prominent phytochemical pesticides in recent years are those derived from neem trees, which have been studied extensively in the fields of entomology and phytochemistry, and have uses for medicinal and cosmetic purposes The neem products have been obtained from several species of neem trees in the family Meliaceae Six species in this family have been the subject of botanical pesticide research They are Azadirachta indica A Juss, Azadirachta excelsa Jack, Azadirachta siamens Valeton, Melia azedarach L, Melia toosendan Sieb and Zucc, and Melia volkensii Gurke The Meliaceae, especially A indica (Indian neem tree), contains at least 35 biologically active principles Azadirachtin is the predominant insecticidal active ingredient in the seed, leaves, and other parts of the neem tree Azadirachtin and other compounds in neem products exhibit various modes of action against insects such as antifeedancy, growth regulation, fecundity suppression and sterilization, oviposition repellency or attractancy, changes in biological fitness, and blocking development of vector-borne pathogens Some of these bioactivity parameters of neem products have been investigated at least in some species of insects of medical and veterinary importance, such as mosquitoes, flies, triatomines, cockroaches, fleas, lice, and others Here we review, synthesize, and analyze published information on the activity, modes of action, and other biological effects of neem products against arthropods of medical and veterinary importance The amount of information on the activity, use, and application of neem products for the control of disease vectors and human and animal pests is limited Additional research is needed to determine the potential usefulness of neem products in vector control programs

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Activity and biological effects of neem products against arthropods of medical and veterinary importance

Larvicides play a vital role in controlling mosquitoes in their breeding sites. The present study was carried out to establish the larvicidal activities of mycosynthesized silver nanoparticles (AgNPs) against vectors: Aedes aegypti and Anopheles stephensi responsible for diseases of public health importance. The AgNPs synthesized by filamentous fungus Cochliobolus lunatus, characterized by UV–Vis spectrophotometry, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The characterization studies confirmed the spherical shape and size (3–21 nm) of silver nanoparticles. The efficacy of mycosynthesized AgNPs at all the tested concentrations (10, 5, 2.5, 1.25, 0.625, and 0.3125 ppm) against second, third, and fourth instar larvae of A. aegypti (LC50 1.29, 1.48, and 1.58; LC90 3.08, 3.33, and 3.41 ppm) and against A. stephensi (LC50 1.17, 1.30, and 1.41; LC90 2.99, 3.13, and 3.29 ppm) were observed, respectively. The mortality rates were positively correlated with the concentration of AgNPs. Significant (P < 0.05) changes in the larval mortality was also recorded between the period of exposure against fourth instar larvae of A. aegypti and A. stephensi. The possible larvicidal activity may be due to penetration of nanoparticles through membrane. Toxicity studies carried out against non-target fish species Poecilia reticulata, the most common organism in the habitats of A. aegypti and A. stephensi showed no toxicity at LC50 and LC90 doses of the AgNPs. This is the first report on mosquito larvicidal activity of mycosynthesized nanoparticles. Thus, the use of fungus C. lunatus to synthesize silver nanoparticles is a rapid, eco-friendly, and a single-step approach and the AgNps formed can be potential mosquito larvicidal agents.

Larvicidal potential of silver nanoparticles synthesized using fungus Cochliobolus lunatus against Aedes aegypti (Linnaeus, 1762) and Anopheles stephensi Liston (Diptera; Culicidae)

BACKGROUND:Aedesaegypti L. is the major vector of dengue fever and dengue hemorrhagic fever. In an effort to find effective tools for control programs to reduce mosquito populations, the authors assessed the acute toxicities of 14 monoterpenoids, trans-anethole and the essential oil of rosemary against different larval stages of Ae. aegypti. The potential for piperonyl butoxide (PBO) to act as a synergist for these compounds to increase larvicidal activity was also examined, and the oviposition response of gravid Ae.aegypti females to substrates containing these compounds was evaluated in behavioral bioassays. RESULTS: Pulegone, thymol, eugenol, trans-anethole, rosemary oil and citronellal showed high larvicidal activity against all larval stages of Ae.aegypti (LC50 values 10.3 – 40.8 mg L −1 ). The addition of PBO significantly increased the larvicidal activity of all test compounds (3 – 250-fold). Eugenol, citronellal, thymol, pulegone, rosemary oil and cymene showed oviposition deterrent and/or repellent activities, while the presence of borneol, camphor and β-pinene increased the number of eggs laid in test containers. CONCLUSIONS: This study quantified the lethal and sublethal effects of several phytochemical compounds against all larval stages ofAedesaegypti, providing information that ultimately may have potential in mosquito control programs through acute toxicity and/or the ability to alter reproductive behaviors. c � 2008 Society of Chemical Industry

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Larvicidal and oviposition‐altering activity of monoterpenoids, trans‐anithole and rosemary oil to the yellow fever mosquito Aedes aegypti (Diptera: Culicidae)

Methanolic leaf extract of Cassia fistula was tested for larvicidal and ovicidal activity against Culex quinquefasciatus and Anopheles stephensi. The extract was found to be more lethal to the larvae of A. stephensi than C. quinquefasciatus with LC(50) values of 17.97 and 20.57 mg/l, respectively. Mean percent hatchability of the ovicidal activity was observed 120 h after treatment. The percent hatchability was inversely proportional to the concentration of extract and directly proportional to the eggs. The egg raft of C. quinquefasciatus was found to be more hatchable than A. stephensi. The results show that the leaf extract of C. fistula is promising as a larvicidal and ovicidal agent against C. quinquefasciatus and A. stephensi.

Larvicidal and ovicidal activity of Cassia fistula Linn. leaf extract against filarial and malarial vector mosquitoes

Bioactive compounds contained in the seed kernel and other parts of the neem tree (Azadirachta indica A. Juss) have been found to show insecticidal activities and other effects in many species of insects. These activities include antifeedancy, growth regulation, fecundity suppression, male sterility, oviposition repellency, changes in biological fitness such as loss of flying ability, immunodepression, enzyme inhibition, splitting of biological rhythms, and so forth. We investigated the ovicidal effects of various formulations of azadrirachtin (AZ) against the mosquitoes Culex tarsalis Coquillett and Culex quinquefasciatus Say. The formulations tested were wettable powder Azad WP10, emulsifiable concentrate Azad EC4.5, and technically pure AZ. The ovicidal activity of the test neem products was influenced by concentration of AZ, age of the egg rafts, and age of the neem preparations. Other factors such as formulation and mosquito species were also involved in the degree of ovicidal activity. When the egg rafts were deposited directly in fresh neem suspension and left there for 4 h before transfer to untreated water, 1 ppm of AZ produced almost 100% mortality in eggs. When egg rafts aged for 0, 4, 8, 12, and 24 h were exposed to 10 ppm neem suspensions for 36 h, the ovicidal activity was only attained in the egg rafts deposited directly (0 h old) in the neem suspension, not in those with ages of 4-24 h. On aging, depending on the formulations and mosquito species, the neem suspensions at 1 ppm completely lost ovicidal activity within 7-20 days. The egg rafts of Cx. quinquefasciatus were more susceptible to the test neem products than those of Cx. tarsalis. The formulated neem products were more persistent and effective than the technical AZ. The wettable powder (WP) formulation was slightly more persistent and effective than the emulsifiable concentrate (EC). The ovicidal activity of the neem products against mosquitoes from the current research clearly demonstrated the potential of neem products as possible ovicides against Culex mosquitoes.

M. S. Mulla

Papers

Ovicidal Activity of Neem Products (Azadirachtin) Against Culex Tarsalis and Culex Quinquefasciatus (Diptera: Culicidae)