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The larvicidal activity of seed and leaf extracts of Calophyllum inophyllum and leaf extract of Rhinacanthus nasutus on the juveniles of Culex quinquefasciatus, Anopheles stephensi and Aedes aegypti was determined. Ethyl acetate (EA) soluble fractions of C. inophyllum and petroleum ether (PE) fraction of R. nasutus extracts showed very high larvicidal activity. Irrespective of the species of the mosquitoes tested, at concentrations ranging from 3.91 to 9.39 ppm, 9.04 to 35.49 ppm and 13.21 to 28.92 ppm of the active fractions of seed and leaf extracts of C. inophyllum and the leaf extract of R. nasutus, respectively, killed 50% of the treated larvae. The fractions also interfered with adult emergence. Exposure of the mosquitoes at any stage of their larval development to less than 0.86, 5.49 and 6.81 ppm of the active fractions of seed and leaf extracts of C. inophyllum and the leaf extract of R. nasutus, respectively, inhibited 50% of the treated larvae from emerging as adults. Experiments under laboratory and semi‐field conditions showed that the activity of the extracts persisted for up to 10 days.

Rearing of Culex quinquefasciatus, Anopheles stephensi and Aedes aegypti larvae in water at concentrations less than the critical concentration for inhibition of adult emergence in 50% of treated larvae (EC 50 ) of the ethyl acetate fractions of Calophyllum inophyllum seed and leaf, Solanum suratense and Samadera indica leaf extracts and the petrol ether fraction of Rhinocanthus nasutus leaf extract, from hatching to emergence signi®cantly decreased the fecundity of the mosquitoes and the hatchability of their eggs. At the highest concentration of 50% EC 50 of the extracts, the decrease in the fecundity over the control ranged between 62.4 and 87.4%. Sterility index of the mosquitoes reared in the media with the dierent extracts at this concentration ranged between 82.8 and 93.3%.

When ration (100%, 50% and 25%) and feeding duration (3, 6, 9, 12 and 24 hr/day) were restricted Danaus chrysippus extended larval period from 6 to 18 days; however, the pupal duration remained constant (6.3 ± 0.4 days) in all the groups. Those fed less than 50% ration and 6 hr/day suffered heavy mortality. Restriction of feeding duration is partially compensated by increasing feeding rate. Despite these restrictions of feeding schedule, the larvae in either series exhibited equal efficiencies of assimilation (44%), and conversion (40%). Hence, the restriction resulted in the production of miniature pupae, whose efficiency to retain body substances in the adult is low (<50%), as against the 60% pupal efficiency exhibited by those fed for 12 or 24 hr/day. ZUSAMMENFASSUNG WIRKUNG VON BESCHRÄNKUNGEN DER FUTTERRATION UND DER FRASSDAUER AUF DIE NAHRUNGSVERWERTUNG BEI DANAUS CH RYSIPPUS (LEPIDOPTERA: DANAIDAE) Wenn die Futterration (100%, 50% und 25%) und die Frasszeit (3, 6, 9, 12, 24 h/d) beschränkt wurde, verlängerte sich die Larvenperiode bei Danaus chrysippus von 6 bis auf 18 d; die Dauer der Puppenruhe blieb dagegen konstant (6,3 ±0,4 d). Hohe Mortalität entstand bei 25% Futterration und ab 6 h Frasszeit. Beschränkung der Frasszeit wird teilweise kompensiert durch zunehmende Frassrate (mg/g Larve/h). Die Frassmenge sank bis auf 33%, die Larvenendgewichte auf 40% (bei 25% Ration) bzw. 33% (bei 3d Fütterung), die Puppengewichte auf 30% bzw.35%. Trotz der Frassbeschränkungen zeigten die Larven in allen Serien gleichen Wirkungsgrad der Assimilation (aufgenommenes Futter‐ minus Kotgewicht) (44%) und der Konversion (Gewichtszunahme) (40%). Der “Puppenwirkungsgrad” (Verhältnis von Adult‐ zu Puppengewicht) sank bis auf 36% gegenüber 60% bei 12‐oder 24‐h/d Fütterung.

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