Whiteflies are harmful to both outdoor and indoor plants by sucking plant sap. Under certain conditions, they can also transmit disease. The whitefly parasite (Encarsia formosa) lays its eggs — as many as 50 to 100 — in both pupae and later larval stages of the white fly, destroying them before they can become adults. The host larva turns black as the parasite develops. It emerges, depending on conditions, in about two weeks. The adults will also feed on the larval juices released when they puncture the larvae.