The nutritional properties of proteins depend upon its amino acid (s) composition and contents. In the digestive system of animals, the digestive enzymes hydrolyze ingested proteins into individual amino acids and then they were combined into the specific proteins that are needed for growth and development. Besides working as a building block of proteins and providing nutritional values to all biological organisms the individual essential and non essential amino acids have also been reported for their additional role in neural transmission, detoxification, energy production and regulation of morphogenetic processes (Chen, 1985; Anand and Anand, 1994; Chang, 2004). Although, the importance of dose and species dependent protein diets on development of insects and the effect of isolated protein on toxicity of larvae have been studied earlier (Chang, 2004) but the association of individual amino acids on developmental period of mosquitoes have been poorly understood. Present investigation reported the changes in developmental period of immature forms of Cx. Quinquefasciatus treated with different concentrations of amino acids in laboratory bioassay.

 

Present study was conducted at Burdwan (23° 16' N, 87° 54' E), West Bengal, India, during June-August 2011. Larvae of Cx. quinquefasciatus were obtained from a laboratory colony maintained in the Mosquito Research Unit, Department of Zoology, The University of Burdwan.

 

During the present study pure samples (LOBA) of amino acids viz. Alanine, Isoleucine, Leucine, Glutamic acid, Tyrosine, Methionine, Glycine and Phenyl Alanine were used in laboratory bioassay. Aqueous extracts of 2%, 3% and 4% were prepared by mixing the necessary amounts (2 mg, 3 mg and 4 mg respectively) of amino acids in 100 mL of double distilled water. Each of the concentrations of amino acid extract (2%~4%) was transferred into sterile glass Petri dishes (9 cm diameter/150 mL capacity). Then, newly hatched 1^st instar larval form of Cx. quinquefasciatus were separately introduced into different Petri-dishes containing graded concentrations and the duration of period for each larval instar and other life cycle stages were recorded up to adult emergence. Different instars were identified as per the diameter of head capsules. Dead larvae if any were identified when they failed to move after probing with a needle in the siphon or cervical region. The experiments were replicated five times and conducted under laboratory conditions at 25~30℃ and 60%~80% relative humidity. A control set was also kept beside with same amount of distilled water and supplementary feeding and 1^st instar mosquito larvae without addition of any amino acids.   

 

3. Result and Discussion
It was found in preliminary experiments that mosquito larvae were sensitive to amino acids. The effects of individual amino acids on the duration of developmental stages were presented in Table 1. The data showed that Alanine, Glutamic acid, Phenyl Alanine and Isoleucine have a growth retardation effect in comparison to control set. On the other hand, Leucine, Tyrosine, Methionine and Glycine accelerate the growth in compareson to control set. However, growth acceleration or retardation effect was found as density independent event. 
 

Table 1 Developmental period analysis of amino acids to Culex quinquefasciatus larva

 

Aromatic amino acids were previously documented to play an important role in various stages of insect developpment including egg hatching factor of mosquitoes, insecticides or repellents, production of toxicity and feeding and food retention activities (Caroci and Noriega, 2003). Present investigation provided first hand information on the effect of individual amino acids extracts in developmental period of immature forms of Cx. quinquefasciatus in laboratory bioassay.

 

UA and AG both study the developmental period of immature stages of Culex quinquefasciatus in laboratory bioassay with aqueous amino acid extracts. GC supervised the whole work and prepared the manuscript. All authors read and approved the final manuscript.

 

The authors are grateful to the Head, Department of Zoology, The University of Burdwan, for the facilities provided. The authors are also grateful to Department of Science and Technology, New Delhi for providing instruments through FIST programme.