%0 Thesis %T TI Biological efficacy evaluation of larvicide formulations in mosquito (Diptera, Culicidae) control %X

Mosquitoes are globally and locally most significant molestants and vectors, transmitting pathogens which may cause humans’ and animals’ severe diseases like West Nile Fever, yellow fever, malaria, dengue and chikungunya frequently with fatal outcome. Mosquito females regular behaviour pattern which includes haematophagous feeding regime on humans and animals gave them highly significant role in public health. Females may intake pathogens at first blood meal on infected host. West Nile Virus circulation in humans, birds, horses and mosquitoes on the Serbian territory has been recently confirmed in several consecutive years. The major highly competent vector is house mosquito, Culex pipiens complex. The species is widely distributed in all parts of Serbia, inhabiting diverse aquatic breeding sites. Invasive, widespread Aedes albopictus is one of the most important vector species of severe human and animal diseases in Europe.  Within mosquito control programs it is essential to modify the strategy of molestant control by vector control, which implies adaptations and optimisations of available methods’ efficacy aiming to the enhanced and faster mosquito suppression/control. Opposite to the most European countries which succeed satisfying mosquito suppression level only by larvicide treatments, Serbia has not reached that level yet, regardless excessive and increasing adulticides treatments in our country. Mosquito control methods should be planed and implemented according to the most recent surveillance of mosquito vector species. Mosquito control plans and programs in Serbia should be precisely based on local conditions and enable economically, ecologically, highly effective meassures which will minimize the negative impact to the equilibrium of the non-target aquatic biota and other organisms that could be endangered by eco-toxicological aspects of applied products into waters of rural and urban areas.  The main objectives of this study aimed to evaluate available larvicide efficacy (cyromazine, diflunbenzuron, pyriproxyfen and polydimethylsiloxane) and to determine susceptibility of the juvenile forms of Cx. pipiens and Ae. albopictus populations to the applied compounds, but also to determine product persistence/longevity in mosquito population reduction treatments.  As a part of chemical control three different Insect Growth Regulators (IGR) types were selected- cyromazine, pyriproxyfen and diflubenzuron as standard/comparative active ingradient. Additionally, silicone (polydimethylsiloxane) based product Aquatain AMF, aimed for physical control, was evaluated.  Mode of IGRs action consists of hormonal disbalance or regular molting process disturbance that reflects to disorder or break of normal physiological functions, resulting by insect death. Aquatain AMF is a silicone-based monomolecular film (polydimethylsiloxane), novel tool, and recently-approved product in the EU for mosquito control affecting mosquitoes’ aquatic developmental stages. AMF spreads spontaneously and rapidly over a water surface. The physical mode of action based on lowering water surface tension prevents mosquito larvae/pupae respiration. Subsequently, AMF disables gravid females to land on the water surface and obstructs the natural oviposition process. According to the multiple effects on all immature mosquito stages, AMF can reduce mosquito density. All selected IGR formulation were granules consisted of ecologically suitable, biodegradable carriers (zeolite, corn cob and Biodac, commercial carrier made of recycled paper). Biological efficacy of all tested IGRs was evaluated in laboratory conditions and subsequently cyromazine was tested in semi-field experiments (in plastic barrels). Following findings obtained cyromazine and diflubenzuron granules were evaluated under field conditions (ditches/channels semirural location).  Tested IGR granules showed high efficacy in Cx. pipiens complex control. Cyromazine granules applied doses were directly equivalent to its efficacy. Granules with 2% cyromazine demonstrated higher, faster and more persistent efficacy comparing to the granules with lower cyromazine content (0.5 %).  Cyromazine 2 granules were two months highly effective against Cx. pipiens juveniles in laboratory conditions. Applied diflubenzuron (1% a.i.) and pyriproxyfen (0.5% a.i.) granules caused complete population reduction (mortality 100%). However, diflubenzuron and pyriproxyfen required longer period to cause same rate of effectiveness. Satisfying efficacy level (LT90) cyromazine achieved more rapidly than other evaluated IGRs. Slowest activity of tested products was recorded in pyriproxyfen treatment.  Bias of all tested IGR formulations were their inability to float. Therefore, until optimised, application of IGR granular formulation should be limited to aquatatic breeding sites with solid base structure (e.g. artificial water recipient, regardless of volume), in which granules would not be lost in mud after they sink from water surface.  Aquatain AMF achieved high mortality rates of juvenile stages of both Ae. albopictus and Cx. pipiens under laboratory conditions. However, Cx. pipiens larvae showed higher susceptibility to AMF compared to Ae. albopictus. The impact on pupae was not different between species. Pupae of both species were highly susceptible. Applied in artificial water recipients, Aquatain AMF inhibits completely (100%) population eclosion to the adult stage of Ae. albopictus. In field conditions Aquatain AMF longevity to suppress Cx. pipiens complex population was estimated in range from 21 to 56 post treatment days, depending on abiotic and biotic factors disturbing applied monomolecular layer.  Recommended dose of this product will not prevent females’ oviposition in a longterm (maximum seven days), but will unable juvenile development hatched from eggs after oviposited on monomolecular layer. Increased dose (10 fold) provides long-term oviposition prevention. Females would be 19 days unable to lay eggs on 10 mL/m2 thick layer.  Implementation of tested novel mosquito control agents which prevent juvenile stages development to adult stage justify possibility of increasing available products of biocides for a sound vector control.  Urban breeding sites are critical and complex to control mosquitoes because of continuous seasonal availability of water bodies and suitable temperatures (frequently higher than in rural areas). Additionally, vicinity of densely populated hosts (humans), generates enormous populations with overlapping generations and presence of all developmental stages from April to October. Adequate selection and application of evaluated biocide agents, adapted to the Cx. pipiens and Ae. albopictus breeding site types would decrease required number of treatments comparing to conventional and biological biocides, especially treatments in urban areas.

%K Mosquitoes control larvicides cyromazine pyriproxyfen %A Kavran, Mihaela %D 2018 %I Author reprint %C Faculty of Agriculture at Novi Sad