Rhodnius prolixus is a blood-gorging insect that is medically important since it transmits Chagas disease via feces and urine that contain the parasite Trypanosoma cruzi. In adult females, ecdysteroid hormone (20-hydroxyecdysone, 20E) is involved in the growth of the ovary and development of eggs post-blood meal (PBM). Halloween genes are essential for ecdysteroid synthesis since they code for cytochrome P450 enzymes in the ecdysteroidogenic pathway. The ecdysone receptor (EcR/USP) binds 20E, resulting in activation of ecdysone-responsive genes. We have identified and characterized the Halloween genes, and the non-Halloween gene, neverland, in the R. prolixus ovary using transcriptomic data. We used BLAST to compare transcriptome sequences with other arthropod sequences to identify similar transcripts. Our results indicate that the Halloween genes, neverland and ecdysone receptor transcripts are present in the ovaries of R. prolixus. We have quantified, by qPCR, Halloween gene transcript expression in the ovary following a blood meal. Most of the Halloween genes are upregulated during the first 3 days PBM. Knockdown of EcR, USP and shade transcripts, using RNA interference, results in a significant reduction in the number of eggs produced and a severe reduction in egg laying and hatching rate. Furthermore, knockdown of the EcR or shade transcripts altered the expression of the chorion gene transcripts Rp30 and Rp45 at day 3 and 6 PBM. These results indicate that ecdysteroids play critical roles in reproduction of female R. prolixus.

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