Limonoids from Citrus reticulata and their moult inhibiting activity in mosquito Culex quinquefasciatus larvae.

Three limonoids, namely limonin, nomilin and obacunone, were isolated from the seeds of Citrus reticulata [Blanco Coorg Mandarin]. Their structures were confirmed by spectroscopic studies. With 4th instar larvae of mosquito Culex quinquefasciatus, the EC50 for inhibition of adult emergence was 6.31, 26.61 and 59.57 ppm for obacunone, nomilin and limonin, respectively. The pattern of mortality at around the EC50 levels was indicative of moult inhibiting activity. The efficacy of a limonoid enriched fraction was similar to that of limonin, probably due to the high content (70%) of limonin.