Enrichment of phenotype among biological forms ofAnopheles stephensiListon through establishment of isofemale lines
Authors: Ghosh Chaitali , Kumar Naveen , Kushwah Raja Babu Singh , Soumya M , Joshi Soumya Gopal , Chethan Kumar R , Alalamath Tejashwini , Srinivasan Subhashini , Subramani Suresh , Kumar Sampath , Swain Sunita 
Published: September 2022

The success of vector management programs relies on knowledge of the biology and genetic make-up of mosquitoes so that they can be interlaced with modern tools for developing suitable intervention strategies. There are many reports available for rearing varied species of mosquito vectors. However, there are limited studies addressing the development of isofemale lines among mosquitoes to homogenize the population to obtain both high-quality genome assemblies and enrichment of phenotype.Anopheles stephensi, an urban malaria vector, is one of the major invasive vectors of malaria distributed throughout the Indian subcontinent, Middle East, and has recently been expanding its range in Africa. With the existence of three biological forms, distinctly identifiable based on the number of ridges on eggs with varying vectorial competence,An. stephensiis a perfect species for developing a method for the successful establishment of isofemale lines, which can be tested for retention of the expected vectorial competence for the various forms. We describe the key steps in the establishment and validation of isofemale lines, which include monitoring the transgenerational fitness traits, morphometrics of eggs, and adult wing size during every generation. After the initial inbreeding depression, as proof of the tedious selection process, no significant morphometric differences were observed in the wings and egg size between the parental and their respective isofemale lines. We observed a significant change in the vectorial competence between the respective isofemale and parental lines enriching expected differential susceptibility towards malaria parasites by the type and intermediate forms. Interestingly, IndCh and IndInt strains showed variations in resistance to different insecticides belonging to all the four major classes. These variant lines have been characterized for their levels of homozygosity both at the phenotype and genotype levels and can be used as a standard reference or as a biological resource for other studies related to urban malaria research.

Author summary

Isofemale lines can be a valuable resource for characterizing and enhancing several genotypic and phenotypic traits. This is the first detailed report of the establishment of two isofemale lines of type and intermediate biological forms inAnopheles stephensi. The work encompasses the characterization of fitness traits among the two lines through a transgenerational study. Further, isofemale colonies were established and used to characterize insecticide susceptibility and vector competence. The study provides valuable insights into the differential susceptibility status of the parental and isofemale to different insecticides belonging to the same class. Corroborating with the earlier hypothesis we exemplify the high vector competence in type form than the intermediate from using homozygous isofemale lines. Using these isofemale lines it is now possible to study host-parasite interactions and identify factors that might be responsible for altered susceptibility and increased vector competence inAn. stephensibiological forms that would also pave way for developing better vector management strategies.