none Pholetesor ornigis (Weed) was reared on potted apple trees in the laboratory to study its reproductive potential as a parasitoid of the spotted tentiform leafminer, Phyllonorycter blancardella (F.). At 23 degree C, a 16:8 (L:D) photoperiod, and with abundant hosts for oviposition, 20 P. ornigis females lived 32 plus or minus 1.6 (x@u- plus or minus SEM) d and parasitized 368 plus or minus 20 hosts larvae. They killed host only by parasitism and did not feed on hosts. The sex ratio of offspring was 1.7:1.0 (male/female), although female offspring outnumbered males during the first 10 d. The net reproductive rate (R sub(o)) under these conditions was 120.1 females per female per generation. Females fed honeydew from Aphis pomi De Geer or sucrose lived 23 plus or minus 8.3 and 21 plus or minus 4.7 d, respectively; those fed on crab apple fruit or given only water lived 8.7 plus or minus 5 and 1.7 plus or minus 0.5 d. Development time from egg to adult increased as constant rearing temperature decreased; the developmental threshold was 9.2 degree C for males and 9.5 degree C for females. Development time was 5 d longer on first-instar hosts than on the other four instars. Implications of these results for biological control of the leafminer are discussed.