Previous studies have shown that the linear furanocoumarin xanthotoxin negatively affects the number of adult offspring that successfully emerge in Copidosoma floridanum, an oligophagous polyembryonic parasitoid of plusiine noctuid moths including the cabbage looper, Trichoplusia ni. As a polyphagous foliage feeder, T. ni larvae may occasionally feed on plants containing furanocoumarins. Here we examine whether xanthotoxin, incorporated into artificial diet, has sex-specific effects on male and female C. floridanum survivorship, clutch size, body size, and sex ratio (of mixed sex broods). Further, we examine whether xanthotoxin affects precocious larval numbers (which have been shown to affect the sex ratio of mixed-sex broods). In addition, we measure the amount of unmetabolized xanthotoxin present in the hemolymph of T. ni, thereby allowing us to examine whether xanthotoxin exerts direct or indirect effects on developing C. floridanum individuals. Lastly, a measurement of C. floridanum’s metabolism of xanthotoxin may illustrate this chemical’s ability to alter sex ratio and clutch size of the parasitoid.