RESUMO
In this paper we investigate in vivo and in vitro effects of orally administered azadirachtin and ecdysone on the phagocytic responses of Rhodnius prolixus 5th-instar larval hemocytes to the yeast Saccharomyces cerevisiae. Groups of insects fed non-treated blood (control) and insects that received azadirachtin plus ecdysone in the blood meal were inoculated with yeast cells in the hemocele. The injected yeast cells disappeared rapidly from the hemolymph, being removed completely by 90min after inoculation. In the insects treated only with azadirachtin the clearance of free yeast circulating particles was significantly delayed compared to the two previously mentioned groups. It was demonstrated that the binding of yeast cells to hemocytes was reduced in the insects treated only with azadirachtin in comparison to both non-treated control and azadirachtin plus ecdysone-treated groups. Phagocytosis occurred when yeast cells were added to hemocyte monolayers prepared with hemolymph from blood fed insects, treated or not with azadirachtin plus ecdysone, so that yeast cells were rapidly bound to hemocytes and internalized in high numbers. By contrast, insects treated with azadirachtin exhibited a drastic reduction in the quantity of yeast cell-hemocyte binding and subsequent internalization. In all groups, the hemocytes attached to the glass slides were predominantly plasmatocytes. The magnitude and speed of the cellular response suggests that hemocyte phagocytosis is one of the main driving forces for the clearance of free circulating yeast cells from the hemolymph. We propose that ecdysone modulates phagocytosis in R. prolixus larvae, and that this effect is antagonized by azadirachtin.
Assuntos
Ecdisona/imunologia , Hemócitos/imunologia , Fagocitose/imunologia , Rhodnius/imunologia , Saccharomyces cerevisiae/fisiologia , Animais , Ecdisona/antagonistas & inibidores , Imunidade Celular , Inseticidas/farmacologia , Larva/imunologia , Limoninas/farmacologia , Rhodnius/microbiologiaRESUMO
Many plant compounds are able to modulate herbivore growth and reproduction by directly interacting with steroid hormones systems. In insects, several classes of phytochemicals, including brassinosteroids and related substances, interfere with molting and reproduction. The effects of the molting-hormone antagonist pesticide DI-31, a brassinosteroid analogue, on Aedes aegypti mosquito larvae were tested in two different exposure scenarios. After static exposure of first-instar larvae, the calculated NOEC, LOEC, and LC(50) values referenced to 19 d were 0.03, 0.036, and 0.04 mg/mL, respectively. Semistatic exposure of fourth-instar larvae revealed them to be slightly less susceptible than the younger larvae (NOEC 0.03 mg/mL, LOEC 0.036 mg/mL, LC(50) 0.049 mg/mL referenced to 19 days). In both cases mortality was immediate and larval development was retarded. This study suggests that A. aegypti could be a useful model for the detection of hormonally active substances such as DI-31.