Investigations on the biology of Microterys flavus, a primary parasitoid wasp of the mango shield scale Protopulvinaria mangiferae were carried out in the laboratory and the results obtained are summarized as follows: The wasp lays eggs mostly to the adults and rarely to the second-instar larvae of the host scale, but not to the first-instar larvae. Number of eggs laid to a host varies from one to five owing to the influence of the host size, one egg to a host in case when the host is smaller than 3 mm in length, or two to five eggs when the host is larger than 4 mm. The threshold temperature and the thermal constant for the development of the wasp from the egg to the adult were 9.5℃ and 257 day-degrees, respectively. On 25℃ and 16-hrs light conditions with honey as food, the average longevity of the wasp was 40 days, the total eggs deposited were 205 in average, of which fiftieth percent were laid in 13 days after the emergence of the wasp, and the net reproduction rate (R_0) and the intrinsic rate of the natural increase (r_m) were calculated as 116.8 and 0.147 per female per day, respectively.