T. Seenivasagan

Oviposition responses of Aedes aegypti and Aedes albopictus to certain fatty acid esters

Laboratory studies were carried out to observe the oviposition responses of Aedes aegypti (L.) and Aedes albopictus (Skuse) to several C21 fatty acid esters. The oviposition activity of these dengue and chikungunya vectors to the long-chain fatty acid esters of C21 length have not been reported earlier. From the multiple choice experiments on oviposition activity in standard mosquito cages, it was observed that compounds hexadecyl pentanoate, tetradecyl heptanoate and tridecyl octanoate presented significant oviposition repellent activity against the two mosquito species, while one compound propyl octadecanoate was found to attract A. aegypti to the treated oviposition substrate at 1- and 10-ppm concentrations. The possible utilization of these esters in integrated vector management is discussed.

Mediation of oviposition responses in the malaria mosquito Anopheles stephensi Liston by certain fatty acid esters

The chemical factors involved in oviposition site selection by mosquitoes have become the focus of interest in recent years, and considerable attention is paid to the chemical cues influencing mosquito oviposition. Studies on synthetic oviposition attractants/repellents of long-chain fatty acid esters against Anopheles stephensi are limited. Screening and identification of chemicals which potentially attract/repel the gravid females to/or from oviposition site could be exploited for eco-friendly mosquito management strategies. The ester compounds demonstrated their ability to repel and attract the gravid A. stephensi females in the treated substrates. Significant level of concentration-dependent negative oviposition response of mosquitoes to octadecyl propanoate, heptadecyl butanoate, hexadecyl pentanoate, and tetradecyl heptanoate were observed. In contrast, decyl undecanoate, nonyl dodecanoate, pentyl hexadecanoate, and propyl octadecanoate elicited concentration-dependent positive oviposition responses from the gravid mosquitoes. Forcing a female to retain her eggs due to unavailability of a suitable oviposition site and attracting them to lay the eggs in a baited ovitraps shall ensure effective control of mosquito breeding and population buildup because the oviposition bioassay target the most susceptible stage of an insect life cycle. Treating relatively smaller natural breeding sites with an effective repellent and placing ovitraps containing an attractant in combination with insect-growth regulator (IGR)/insecticide would be a promising method of mosquito management.

Electrophysiological, flight orientation and oviposition responses of three species of mosquito vectors to hexadecyl pentanoate: residual oviposition repellent activity.

ABSTRACT Understanding on the chemical ecology of mosquito behavior is of paramount importance in developing control programs employing attractants and repellents, Several workers focused on topical repellents and oviposition attractants of mosquitoes, however, only limited work has been accomplished on mosquito oviposition repellents, The present systematic investigation provides evidence on the effectiveness of a C21 fatty acid ester- hexadecyl pentanoate, to stimulate antennal olfactory receptors of Aedes aegypti (L.), Ae. albopictus (Skuse), and Anopheles stephensi (Liston) that mediate their long-range olfaction guided flight orientation behavior by repelling the gravid females of these mosquito vectors in the olfactometer. The compound loaded onto an effervescent tablet retained its repellent property in the treated substrates for up to 1 wk at 10 mg/L. In places, where the mosquito breeding habitats are near to human habitations, could be treated with hexadecyl pentanoate to repel the ovipositing gravid females as a component of the integrated approach for mosquito management by disrupting the mosquito life cycle and population growth.

Synthesis and bio-evaluation of aryl hydrazono esters for oviposition responses in Aedes albopictus

A novel series of aryl hydrazono esters (AHE) (1-13) were synthesized (yield 76-98%) to study the oviposition responses in Aedes albopictus (Skuse) mosquitoes for the first time. At a concentration of 10μgml(-1) in dual choice experiment, among the screened compounds, AHE-12 showed remarkable oviposition attractant activity with an oviposition activity index (OAI) of +0.299 (greater than 95% confidence limit) comparable to p-cresol (OAI +0.320) which is well-reported oviposition attractant for Aedes aegypti. Conversely, AHE-10 exhibited highest oviposition deterrent activity with OAI -0.247. The possible utilization of these compounds will be in integrated vector management strategies.

Electroantennogram, flight orientation and oviposition responses of Anopheles stephensi and Aedes aegypti to a fatty acid ester-propyl octadecanoate

Studies were carried out to evaluate the role of a C(21)-fatty acid ester; propyl octadecanoate (PO) for olfaction-mediated behavioral responses of urban malaria vector, Anopheles stephensi and dengue vector, Aedes aegypti mosquitoes using electroantennogram (EAG), flight orientation and oviposition experiments. Dose dependent electrophysiological responses were recorded for PO from the antenna of both mosquito species in which 10(-5) g elicited significant EAG response. An. stephensi exhibited 2.4, 4.2 and 5.5 fold increased EAG response compared to control, while Ae. aegypti showed 1.9, 4.6 and 5.8 fold EAG responses respectively at 10(-7) g, 10(-6) g and 10(-5) g doses. In the Y-tube olfactometer, 77-80% gravid females of An. stephensi, and 64-77% of Ae. aegypti were caught in the chambers releasing 10(-6) g and 10(-5) g plume of PO. The synthetic fatty acid ester loaded onto an effervescent tablet at 0.1 mg/L, 1 mg/L and 10 mg/L elicited increased ovipositional responses from gravid mosquitoes compared to control. The oviposition activity indices (OAI) of An. stephensi females were +0.40, +0.51 and +0.58, whereas the OAI for Ae. aegypti females were +0.05, +0.36 and +0.57 respectively in 0.1, 1, 10 mg/L of PO; indicated concentration dependent increased egg deposition. Similarly, in the residual activity studies, oviposition substrates treated with PO on effervescent tablet at 1mg/L and 10mg/L received significantly increased egg deposition by gravid females of both mosquito species for up to 1 week compared to control substrates. PO can potentially be used in ovitraps to monitor An. stephensi and Ae. aegypti populations in the vector surveillance programs.

Behavioral and electrophysiological responses of Culex quinquefasciatus to certain fatty acid esters.

Oviposition response of gravid Culex quinquefasciatus females to a series of synthetic fatty acid esters was evaluated at 10ppm under laboratory conditions. Octyl tridecanoate and propyl octadecanoate elicited 85% and 73% increased ovipositional responses respectively, compared to control, among the 16 esters tested. Other 14 esters showed highly significant repellency (67-96%) to gravid females. Standard 3-methyl indole received 69% increased egg deposition compared to control. In the Y-tube olfactometer, gravid C. quinquefasciatus females exhibited 78, 64% and 58% orientation respectively to octyl tridecanoate, propyl octadecanoate and 3-methyl indole. Gravid females exhibited 19-41% reduced orientation toward treatment odors of other esters significantly different from respective control. Electroantennogram studies revealed 4-18-fold increased antennal response, in which 3-methyl indole, octyl tridecanoate and propyl octadecanoate elicited 8-, 18- and 15-fold EAG response respectively, compared to control. Relative EAG response of octyl tridecanoate compared to standard 3-methyl indole was significantly different. Reduced EAG responses were elicited by FAE-06, -08, -13, -14 and -15, while the relative EAG responses of other esters were at par with the standard stimulus. These, esters could be utilized potentially as oviposition attractants and repellents against C. quinquefasciatus females to reduce the breeding in polluted water along with existing integrated vector control methods.