5% v/v), as a control. The number of parasites was then counted directly in a hemocytometer chamber. Fifth-instar R. prolixus nymphs were obtained from a colony reared and maintained in our laboratory at a relative humidity of 50–60% and at 27 ± 2 °C as described by Azambuja and Garcia (1997). Insects were starved for 20–30 days before being chosen for experiments. During the experiments they were fed on defibrinated rabbit blood through a membrane feeding apparatus ( Garcia et al., 1984). A control group (C) was fed
with blood and DMSO (0.5 μl/mL of blood) used as the solvent, and the infected groups (CC) with blood containing 1 × 107T. cruzi Dm28c clone/mL and with DMSO (0.5 μl/mL of blood). Only the fully engorged insects, which fed around 250 μL of blood selleck compound (estimated by weighing the insects before and after feeding), were used in the experiments. This amount of blood ingested corresponds to approximately 2.0 × 106T. www.selleckchem.com/products/CAL-101.html cruzi Dm28c epimastigotes/infected insect. All insects were raised and maintained as previously described ( Azambuja and Garcia, 1997). To determine parasite infection in insects, the whole digestive tract was homogenized in 1 mL of sterile phosphate buffered saline
(PBS, phosphate 0.01 M and NaCl 0.15 M, pH 7.2) and the number of parasites was counted directly in a hemocytometer chamber. A preliminary test of parasite infection was made with control insects and physalin oral treated insects from 6 to 30 days alter feeding. The infection, when established in the midgut, is more intense from 8 to 13 days (Castro et al., 2012). In the
case of the physalins group the parasites did not succeed in maintaining the infection for the full period of 30 days. Therefore we standardized the parasite infection count to the early period of 8–13 days, when the infection is higher. R. prolixus fifth-instar Urease nymphs were treated with physalin B by oral feeding, topical or contact applications as described below: Physalin B was diluted to a final concentration of 1 μg/mL of blood meal, based on the results obtained in a previous research (Castro et al., 2008 and Castro et al., 2009). A group of insects was fed blood containing physalin (represented as F) and another group was fed on blood containing physalin B and parasites (2 × 106T. cruzi Dm28c clone/mL of blood) (FC). Physalin B stock was diluted in Ringer buffer (0.2 M Na2CO3, 0.2 M NaHCO3, pH 9.4) to a final concentration of 10 μg/mL, and 2 μL was applied on the thorax of the insect. We worked with an initial dose 10 times higher (10 μg/mL) than the oral treatment since the application was not applied directly into the digestive tract, and therefore the compound needed to pass through the cuticle, hemocele and perimicrovillar membrane to reach the gut. After 10 min, the insects were allowed to feed on blood containing parasites (2 × 106T. cruzi Dm28c clone/mL, FTC) or not (FT).