Tuta absoluta, a destructive tomato pest worldwide, has recently invaded China. Neochrysocharis formosa, a host-feeding parasitoid wasp, has thelytokous (TH) and arrhenotokous (AR) strains with sympatric distributions in many regions of China. To clarify the biocontrol potential of the two strains, we evaluated the host-killing behaviors on different instar larvae of T. absoluta and the life history traits of the two strains reared on T. absoluta. Our results showed that both strains can parasitize, feed and directly kill 1st to 3rd instar T. absoluta larvae. In contrast, in 4th instar larvae, both strains only kill larvae by host-stinging. When the 1st instar host was constantly provided, the TH strain showed significantly greater biocontrol potential than the AR strain. The former had higher fecundity (2.10-fold), killed more larval hosts (1.57fold), survived longer (1.37-fold), and had more offspring (2.07-fold) that successfully emerged. In summary, the TH strain of N. formosa is a better candidate for biological control than the AR strain of T. absoluta. These results will play a pivotal role in building a biological control technology system for the notorious pest T. absoluta.