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This study assessed new insecticidal activities of essential oils from Lippia sidoides and Croton species (Croton zehntneri, Croton nepetaefolius, Croton argyrophylloides, and Croton sonderianus) against Aedes aegypti mosquito. In addition, the acute toxicity upon mice was determined. All essential oils showed inhibition of egg hatching, with IC50 values ranging from 66.4 to 143.2 μg mL(-1), larvicidal activity with LC50 ranging from 25.5 to 94.6 μg mL(-1), and pupicidal action with PC50 ranging from 276.8 to over 500 μg mL(-1). Only L. sidoides, C. zehntneri, and C. argyrophylloides essential oils were able to inhibit the oviposition of female gravid mosquitoes with OD50 values of 35.3, 45.3, and 45.8 μg mL(-1), respectively. Oral acute toxicity in mice showed that C. sonderianus and C. argyrophylloides oils are nontoxic (LD50 > 6,000 mg.kg(-1)) while C. nepetaefolius, C. zehntneri, and L. sidoides oils are moderately toxic (LD50 3,840; 3,464, and 2,624 mg.kg(-1), respectively). The results indicate that these oils are promising sources of bioactive compounds, showing low or no toxicity to mammals.

Seed ethanolic extracts of 21 Brazilian plants were evaluated for ovicidal, larvicidal, and pupicidal activities against insecticide-susceptible (SS) and field-collected (FC) strains of Aedes aegypti (L.) (Diptera: Culicidae), as well as for their effects on nontarget organisms. Myracrodruon urundeuva Fr. Allemao extract was highly toxic to both mosquito strains. Schinopsis brasiliensis Engler extract showed low toxicity and was 38-68 times less toxic to Ae. aegypti larvae than was M. urundeuva extract. The pupicidal activity (LC50) of 14 plant seed extracts ranged between 9 and 433/g/ml, and toxicities were comparable to both mosquito strains. Piptadenia moniliformis Benth. and Luetzelburgia auriculata (Allemao) Ducke extracts showed the highest activities against pupae of FC and SS strains. None of the extracts showed 100% ovicidal activity. In addition, the active extracts did not show high acute toxicity to mice (LD50 > 1.5 g/kg), except that of Enterolobium contortisiliquum (Vell.) Morong. Most of the active extracts exhibited low toxicity against brine shrimp (Artemia sp.) nauplii. The extracts of M. urundeuva, P. moniliformis, and L. auriculata are promising sources of recognized classes of insecticidal compounds with good selectivity against immature stages of Ae. aegypti.

The mosquito Anopheles gambiae is the principal vector for malaria in sub-Saharan Africa. The ability of A. gambiae to transmit malaria is strictly related to blood feeding and digestion, which releases nutrients for oogenesis, as well as substantial amounts of highly toxic free heme. Heme degradation by heme oxygenase (HO) is a common protective mechanism, and a gene for HO exists in the An. gambiae genome HO (AgHO), although it has yet to be functionally examined. Here, we have cloned and expressed An. gambiae HO (AgHO) in E. coli. Purified recombinant AgHO bound hemin stoichiometrically to form a hemin-enzyme complex similar to other HOs, with a K of 3.9 ± 0.6 μM; comparable to mammalian and bacterial HOs, but 7-fold lower than that of Drosophila melanogaster HO. AgHO also degraded hemin to biliverdin and released CO and iron in the presence of NADPH cytochrome P450 oxidoreductase (CPR). Optimal AgHO activity was observed at 27.5 °C and pH 7.5. To investigate effects of AgHO inhibition, adult female A. gambiae were fed heme analogues Sn- and Zn-protoporphyrins (SnPP and ZnPP), known to inhibit HO. These led to a dose dependent decrease in oviposition. Cu-protoporphyrin (CuPP), which does not inhibit HO had no effect. These results demonstrate that AgHO is a catalytically active HO and that it may play a key role in egg production in mosquitoes. It also presents a potential target for the development of compounds aimed at sterilising mosquitoes for vector control.