RNAi-mediated knockdown of transformer-2 in the predatory mite Metaseiulus occidentalis via oral delivery of double-stranded RNA

Little is known about the process of sex determination at the molecular level in Metaseiulus occidentalis, a parahaploid species and natural enemy of phytophagous pest mites. Detailed knowledge of the sex-determination pathway could allow genetic manipulation of M. occidentalis to produce more female offspring, which could improve its effectiveness as a biological control agent. RNA interference is useful for assessing the function of putative sex-determination genes by reducing or eliminating gene expression. In many insect species the transformer-2 (tra-2) gene is an upstream regulatory element in the sex-determination cascade, and knockdown of tra-2 expression can alter the sex ratio. We assessed whether oral delivery of tra-2 double-stranded RNA to M. occidentalis virgin females would affect the sex of her progeny. Females that ingested tra-2 dsRNA produced significantly fewer eggs compared to control females suggesting that tra-2 is somehow involved in reproduction by females. However, the sex ratio of the few progeny that were laid was not altered, so it is unclear whether tra-2 is involved in sex determination. This is an initial step towards elucidating the molecular components of sex determination in M. occidentalis.