Functional response and density dependent feeding interaction of Oreochromis niloticus against immatures of Culex quinquefasciatus

India, mosquito-borne protozoans, nematodes and viral diseases are responsible for high mortality and morbidity. Mosquito-borne diseases such as malaria, filariasis and dengue cause huge medical, financial and social burden in developing and under-developed countries. Increase in the incidence of mosquito-borne diseases mainly occur due to rapid and unplanned urbanization, poor sanitation, widely available temporary and permanent breeding grounds of mosquitoes, development of insecticide resistance in vector species due to wide and injudicious application of chemical insecticides and poor prophylactic and therapeutic measures. Lymphatic filariasis is mainly caused by the nematode Wuchereria bancrofti. The disease is transmitted primarily by the mosquito Culex quinquefasciatus; however, Mansonia annulifera and Ma. uniformis also act as a vector, where the causative organism is the nematode Brugia malayi. The National Vector Borne Disease Control Programme, Govt. of India has estimated that filariasis is endemic in 255 districts in 21 states and Union Territories. The population of about 650 million in these districts is at risk of lymphatic filariasis. This situation demands the implementation of effective vector control strategy to reduce the higher incidence of mosquito-borne diseases. Being a holo-metabolous insect, mosquito undergoes four stages in their life cycle, viz. egg, larva, pupa and adult. Due to the restricted aquatic habitat, larval stage is the most important target of many effective vector control operations. Development of insecticide resistance in vector population and degradation of environmental health and undesirable effect on non-target population demands the application of biological control methods in vector control operations1. Biological vector control means the use of natural enemies/predators to reduce vector population in their natural habitat using trophic level relationship, i.e. the predators present in higher trophic level are used to feed on organisms at lower trophic level. For example, Gambusia affinis (Mosquito fish), a natural mosquito predator can consume mosquito larvae as their prey. The Nile Tilapia (Oreochromis niloticus) is a cichlid fish endemic to Africa and Middle East Asia. It is a voracious omnivorous feeder having distinctive, regular, vertical stripes throughout their body up to the edge of caudal fin. This exotic fish species was introduced in India during late 1987. Earlier studies have reported the larvivorous potentiality of O. niloticus in laboratory and field conditions against the mosquito larvae2. The present investigation was carried out to establish the feeding interaction of O. niloticus and mosquito larvae in laboratory bioassay. A detailed numerical analysis was also carried out to establish the particular type of functional response of the predatory fish against the larval forms of common filarial vector, Cx. quinquefasciatus. In the present investigation, larvae of mosquito Cx. quinquefasciatus were collected from cemented drains and temporary aquatic bodies surrounding Bankura Christian College campus, West Bengal (India) during July–August 2016 and brought to the Department of Zoology. They were transferred in a plastic tray and reared in the departmental laboratory with artificial food. Predatory fishes, i.e. O. niloticus were collected from irrigation canals of Bankura and transferred in a glass aquarium maintained in the laboratory. Some aquatic weeds were placed in the aquarium to simulate natural conditions. After acclimatization for three days in the laboratory, with mosquito larvae as natural food, III instar larvae of Cx. quinquefasciatus were separated from the mixed population of collected larvae and transferred in a glass beaker. A single O. niloticus was allowed for predation with Short Research Communications