An Important Parasite of the Greenhouse White-fly (Trialeurodes vaporariorum, Westwood)

1.—Encarsia formosa, Gahan, is a Chalcid wasp that parasitises the white-fly, Trialeurodes vaporariorum, Westw., a single female ovipositing in 50 or more young pupae of the host. The larvae of the parasite, on hatching from the egg, destroys the white-fly pupa, the skin of which becomes black in colour, thus distinguishing the parasitised pupa from the normal white scales and pupa of the white-fly.2.—The parasite is parthenogenetic, males, probably impotent, only appearing when temperatures are low.3.—The life-history of the parasite occupies at least 28 days, and adults may remain in the scales for some time before cutting their way out by a circular hole in the roof of the scale. The adult is capable of travelling over large areas in glasshouses.4.—Low temperatures militate seriously against the increase of the parasite, which is probably a tropical insect and has possibly been imported into this country from India.5.—Fumigation with hydrocyanic acid gas, as practised commercially for the control of white-fly, does not affect the parasites.6.—The parasite is best distributed by detaching the black pupae of white-fly from the foliage, though 20 per cent, may be injured in this way. An almost complete emergence is obtained by cutting branches from plants and pinning them to the plants in houses where distribution is desired, but this involves risk of infecting the houses with various pests and diseases.