Effects of temperature and nutrition stress on Anopheles stephensi, an Indian urban malaria vector

Background: Changing climate and complexity in ecological landscape can potentially expand the geographic distribution of mosquitoes (Diptera: Culicidae) to adapt and transmit various vector-borne diseases like malaria globally. Anopheles stephensi is a potential urban malaria vector in the Indian subcontinent. Temperature and nutrients are the important environmental stressors, which influence the life cycle and vector competence of mosquitoes. Methods: Three experimental setups were designed in the laboratory by exposing An. stephensi to low-temperature (LT, 4°Cand 18±1°C), high-temperature (HT, 35.5±1°C) and nutrition-deficient (NT, 33 mg) conditions. Stress was induced to both juvenile and adult stages for eight consecutive generations. Data of life-stage parameters were recorded. Additionally, LT, HT and NT strains were infected with in vitro culture of Plasmodium falciparum to compare their vectorial competence. Cytological analysis using the ovarian polytene chromosomes of the three stressed strains was carried out to check the structural differences in chromosomal arms due to extreme stress. Through predictive mathematical modelling using linear regression analysis, we estimated the number of generations required for the stressed lines to become comparable to the control lines. Results: Fecundity, egg–wing sizes, egg-to-adult developmental time, pupal weight, male-to-female ratio, and longevity of adults were decreased in HT and NT lines, whereas these parameters were increased in LT lines. The HT and NT lines developed faster from egg to adult emergence (7.5 and 11 days), whereas the duration was longer (25 days) in the LT line. The oocyst infection rates in in-vitro Plasmodium falciparum were higher in HT, LT, and NT lines than the control line. The NT line revealed paracentric inversions on the 3L polytene chromosome arm in 2 locations. Further, the predictive model suggested faster adaptation of the LT line than HT and NT lines. Conclusion: Being an invasive species and responsible for urban malaria transmission, the present multi-transgenerational laboratory-based study provides novel insights into the effects of stress on the life cycle, vectorial competence, cytology and rate of adaptation of An. stephensi . The findings aid in assessing disease risk and developing suitable intervention measures.