Assessment of the insecticidal potential of Eucalyptus urograndis essential oil against Rhodnius neglectus Lent (Hemiptera: Reduviidae).

The resistance of triatomines to pyrethroids has been reported in several Latin American countries, including Brazil, indicating the need for the development of new approaches for the control of vectors of the Chagas disease. In here, we evaluated the insecticidal potential of the essential oil of Eucalyptus urograndis (Myrtaceae) against unsexed third and fourth instars of Rhodnius neglectus Lent (Hemiptera: Reduviidae) in topical application, fumigation, surface contact, and repellency . The insecticidal activity of the essential oil tested was detected by topical application (LD50 = 0.1731 µL/insect and LD99 = 0.2948 µL/insect for 24 h), fumigation (LC50 = 0.021 mL/mL air and LC99 = 0.1525 mL/mL air for 24 h) and surface contact (LC50 = 0.7073 µL/cm(2) and LC99 = 4.59 µL/cm(2) for 24 h). Mortality observed after 48-72-h exposure was very high and did not allow for any adjustment of the mortality curve. In the repellency assay, an effect was observed on 80% of tested nymphs. However, no repellency was observed after 24 h of exposure. Eucalyptus urograndis essential oil has a high insecticidal and repellent potential for R. neglectus nymphs, whether serving as a molecular model for new substances or as an alternative for the control of these insects.

Impacts of Synergy-505 on the functional response and behavior of the reduviid bug, Rhynocoris marginatus.

The impact of the insecticide, Synergy-505 (chlorpyrifos 50% and cypermethrin 5% E.C), on the functional response, predatory behavior, and mating behavior of a non-target reduviid, Rhynocoris marginatus (Fabricius) (Hemiptera: Reduviidae), a potential biological control agent, were studied. Though both normal and Synergy-505-exposed R. marginatus exhibited Holling's type II curvilinear functional response, Synergy-505 caused a less pronounced type II functional response with reduced numbers of prey killed, attack rate, searching time, and prolonged handling time in 4th and 5th nymphal instars and adult males and females reflecting reduced predatory potential. Synergy-505 also delayed the predatory and mating events. The impacts of Synergy-505 on functional response, predatory behavior, and mating behavior were more evident at higher concentrations of Synergy-505.

Hydrogen peroxide detoxification in the midgut of the blood-sucking insect, Rhodnius prolixus.

Here we investigated H2O2 production and detoxification in the hematophagous hemiptera, Rhodnius prolixus. Superoxide dismutase (SOD) catalyzes the dismutation of superoxide radical (O2-). This reaction produces hydrogen peroxide, which is scavenged by antioxidant enzymes such as catalase (CAT). SOD and CAT activities were found in all tissues studied, being highest in the midgut. CAT was dose-dependently inhibited in vivo by injections of 3-amino-1,2,4-triazole (AT). Insects treated with AT showed a twofold increase in H2O2 levels. Injection of DL-buthionine-[S, R]-sulfoximine (BSO), an inhibitor of glutathione synthesis, also resulted in a fourfold increase in H2O2, together with stimulation of CAT activity. Simultaneous administration of both AT and BSO had a synergistic effect on midgut H2O2 content. Taken all together, our results suggest that CAT and glutathione-dependent mechanisms cooperate to control H2O2 concentration in the midgut cell and prevent hydroxyl radical generation by Fenton reaction in this tissue.

Cytoskeleton elements mediate the inhibition of the (Na++K+)atpase activity by PKC in Rhodnius prolixus malpighian tubules during hyperosmotic shock.

In a previous paper, we observed that the specific activity of (Na++K+)ATPase of the isolated Malpighian tubules from Rhodnius prolixus is inhibited by protein kinase C (PKC) during hyperosmotic shock [Arenstein et al., J Membr Biol 146:47-57 [1995]; Caruso-Neves et al., Z Naturforsch 53c:911-917 [1998]). In the present paper, we study the involvement of the cytoskeleton in this process using isolated Malpighian tubules of Rhodnius prolixus. We observed that pre-incubation of the Malpighian tubule cells in hyperosmotic media decreases the specific activity of (Na++K+)ATPase by 90%. This effect was completely reversed when colchicine, which disrupts microtubules, or cytochalasin B, an inhibitor of actin microfilament polymerization, were added to the media in a dose-dependent manner. The maximal reversion was obtained with colchicine 7.0 microM or cytochalasin B 5.0 microM. The simultaneous addition of sphingosine 50 ng/mL, an inhibitor of PKC, to 10 microM colchicine or 5 microM cytochalasin B, in hyperosmotic media, did not change the stimulatory effect of these drugs on the specific activity of (Na++K+)ATPase. On the other hand, the co-incubation of TPA 20 ng/mL, an activator of PKC, to colchicine or cytochalasin B within hyperosmotic media, abolished the stimulatory effect of these drugs on the specific activity of (Na++K+)ATPase to a similar extent as hyperosmotic shock. These results suggest that inhibition of the (Na++K+)ATPase of the isolated Malpighian tubules from Rhodnius prolixus by PKC during hyperosmotic shock is mediated by cytoskeletal elements.