The importance of sex ratio s in the biology and biocontrol application of egg parasitoids can be summarized as the cost of producing males. For both the biocontrol practitioner and the biocontrol agent a surplus of healthy fecund females is highly desirable. The sex ratio investment advice of a biological banker might be to maximize the total number of reproductive females and minimize the number of males. In this chapter we will describe two inherited genetic element s found in several Trichogramma species that can be considered either excellent or terrible investment options. These non-Mendelian genetic elements effectively distort offspring sex ratios in a manner that can be called selfish- since both promote their own transmission at the expense of host nuclear genes. One, a bacterium called Wolbachia can convert haplodiploid females into fully functional completely parthenogenetic organisms (Stouthamer et al. 1993). In fact, several Wolbachia infected species are only known from parthenogenetic females- few or no males are found (Huigens and Stouthamer 2003). The other, a nuclear “extra” chromosome called PSR (Paternal Sex Ratio) found only in male haplodiploids behaves in a manner that can only be described as extremely selfish. The PSR chromosome turns eggs destined to develop as females into males that carry the PSR chromosome (Werren and Stouthamer 2003). These two sex ratio distorters have opposite but sometimes complimentary consequences in parasitoid populations. We will discuss the biology and applied potential of both these sex ratio distorters in Trichogramma species.