Essential oil from Piper tuberculatum Jacq. (Piperaceae) and its majority compound ß-caryophyllene: mechanism of larvicidal action against Aedes aegypti (Diptera: Culicidae) and selective toxicity.

Synthetic insecticides have been the primary approach in controlling Aedes aegypti; however, their indiscriminate use has led to the development of resistance and toxicity to non-target animals. In contrast, essential oils (EOs) are alternatives for vector control. This study investigated the mechanism of larvicidal action of the EO and ß-caryophyllene from Piper tuberculatum against A. aegypti larvae, as well as evaluated the toxicity of both on non-target animals. The EO extracted from P. tuberculatum leaves was majority constituted of ß-caryophyllene (54.8%). Both demonstrated larvicidal activity (LC50 of 48.61 and 57.20 ppm, p < 0.05), acetylcholinesterase inhibition (IC50 of 57.78 and 71.97 ppm), and an increase in the production of reactive oxygen and nitrogen species in larvae after exposure to the EO and ß-caryophyllene. Furthermore, EO and ß-caryophyllene demonstrate no toxicity to non-target animals Toxorhynchites haemorrhoidalis, Anisops bouvieri, and Diplonychus indicus (100% of survival rate), while the insecticide α-cypermethrin was highly toxic (100% of death). The results demonstrate that the EO from P. tuberculatum and ß-caryophyllene are important larvicidal agents.

In vitro germination of zygotic embryos of hybrid BRS Manicoré (E. guineensis X E. oleifera).

The interspecific oil palm hybrid BRS Manicoré (E. guineensis x E. oleifera) has superior agronomic characteristics. However, the germination rate is low (30%) and the process is slow when the seeds are sown in a conventional form. The purpose of this study was to optimize the in vitro germination of zygotic embryos of this hybrid comparing seed lots. The viability of zygotic embryos was evaluated by the tetrazolium test (0.075%) for 4 h. The embryos were cultured on MS and Y3 culture media, with and without the addition of NaH2PO4, as well as on MS, MS1/2 and N6 medium. In MS medium containing NaH2PO4, the germination rate was increased from 40 to 70% in comparison with the medium without sodium phosphate. The comparison between the culture media MS, MS 1/2, N6 and Y3 showed that 75% of zygotic embryos cultured in the Y3 medium formed whole plants (with roots and shoots defined), a higher percentage than embryos cultured on MS, MS 1/2 and N6 media (46, 35 and 17% respectively). In the same Y3 culture medium, the embryos were larger (36% ≥ 2 cm and 30% ≥ 5 cm) than in the other media. Results obtained by the tetrazolium test were similar to those of germination, showing the effect of the genotype of each seed lot. For the germination and development of plantlets it is essential to add NaH2PO4 to a culture medium containing no phosphate or with a low phosphate concentration.