Egg‐float ridge number in Anopheles stephensi: ecological variation and genetic analysis

Abstract

Abstract. Eight Indian laboratory stocks of Anopheles stephensi Liston could be grouped into three categories with, respectively, 14–22, 12–17 and 9–15 ridges on the egg‐floats. The mode number of ridges among the eggs laid by individual females in these stocks was 16–19,13‐16 and 10–14, respectively. The category with the highest egg‐float ridge number corresponded with the type‐form and the lowest with var. mysorensis Sweet and Rao; the new egg‐float category with ridge number modes of thirteen to sixteen was designated as ‘intermediate’. All three forms, i.e. type‐form, intermediate and mysorensis were observed in semi‐urban areas while only intermediate and mysorensis were seen in rural areas. Breeding experiments indicated no post‐copulatory barriers between the populations. Likelihood analysis of the results of crosses and back crosses indicated that variation in ridge number is controlled by more than one genetic factor. The stocks with different ridge numbers are best considered as ‘ecological variants’.

The type and mysorensis forms of the Anopheles stephensi (Diptera: Culicidae) in India exhibit identical ribosomal DNA ITS2 and domain-3 sequences

“…Approximately, 12% of all malaria cases in India are transmitted by this species of Anopheles (Adak et al 2005). Two races in this species, called A. stephensi stephensi (type form) and A. stephensi variety mysorensis, have been reported by several investigators on the basis of differences in length and width of eggs, length of the egg floats, and the number of ridges on the egg float Subbarao et al 1987;Sweet and Rao 1937). The type form is predominantly an urban mosquito while variety mysorensis is mainly found in rural areas (Rao 1984;Rutledge et al 1970;Subbarao et al 1987).…”

“…Two races in this species, called A. stephensi stephensi (type form) and A. stephensi variety mysorensis, have been reported by several investigators on the basis of differences in length and width of eggs, length of the egg floats, and the number of ridges on the egg float Subbarao et al 1987;Sweet and Rao 1937). The type form is predominantly an urban mosquito while variety mysorensis is mainly found in rural areas (Rao 1984;Rutledge et al 1970;Subbarao et al 1987). A third morphological variant of this species called "intermediate" was also found in India and Iran (Subbarao et al 1987;Vatandoost et al 2006).…”

“…The type form is predominantly an urban mosquito while variety mysorensis is mainly found in rural areas (Rao 1984;Rutledge et al 1970;Subbarao et al 1987). A third morphological variant of this species called "intermediate" was also found in India and Iran (Subbarao et al 1987;Vatandoost et al 2006). Like A. stephensi variety mysorensis, the intermediate form is mostly found in rural settings (Subbarao et al 1987).…”

Ecological variation and resistance levels to propoxur and chlorpyrifos in Anopheles stephensi (Diptera: Culicidae), a malaria mosquito from India

“…Classification of the vector into ecological variants has a propounding effect on disease transmission (Shetty et al, 1999). The type and intermediate forms that are predominant in urban and semi-urban areas have been reported to be vectors, while mysorensis, reported to be predominant in rural areas, has been determined to be a non-vector (Sweet and Rao, 1937;Rao, 1984;Subbarao et al, 1987;Shetty et al, 1999). The result of the present study is in accordance with the earlier reports where type and intermediate forms have been found in urban and semi-urban areas.…”

“…The numbers of ridges for the variants are 14 -22 (type form), 9-15 (mysorensis) and 12-17 (intermediate). The type and intermediate forms have been found in urban and semi-urban areas and reported to be vectors; the mysorensis form has been found to be predominant in rural areas and reported as a non-vector (Subbarao et al, 1987;Shetty et al, 1999). The type form has been found to be exclusively domestic in all seasons, whereas mysorensis occupies the outdoor niche during monsoon and post-monsoon seasons with a spillover into domestic sites during summer periods of ecological stress (Nagpal et al, 2003).…”