The attempt to effect the control of insect pests by the introduction of other insects parasitic elsewhere on members of the same or allied genera, and their propagation in the laboratory on their new host until sufficient numbers for field distribution have been obtained, represents a recent and highly important development of Applied Entomological Science. In this connection may be instanced the introduction into Hawaii of parasites destructive to the sugar-cane leafhopper; the introduction of the Scoliid Tiphia parallela, Smith, from Barbados into Mauritius for the control of the Melolonthid Lachnosterna (Phytalus) smithi, Arrow, a sugar-cane pest; the importation into the U.S.A. of Chalcid, Tachinid, and other parasites of the gipsy and brown-tail moths; and the recent despatch to New Zealand of Tachinid files destructive in England to Forficulidae.