438 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1931 



ture to the native abode of the pests and their parasites. These men 

 go for a year, or several years, or more, and establish laboratories in 

 a crucial area where the host and its enemies are carefully studied 

 before shipments of parasites to this country are attempted. Such 

 studies are in the nature of bringing out facts that will lead to the 

 intelligent manipulation of the parasites when they are transported, 

 and even more for the sake of ascertaining whether the beneficial 

 primary parasite may have parasites of its own, or secondary para- 

 sites, which, if introduced, would more or less impair the efiiciency of 

 the primary species. By means of laboratory technique the secondary 

 parasites may be eliminated and a quantity of free primaries ob- 

 tained for shipment. Other species have no secondary enemies. 

 Native men, women, and children are employed to collect the para- 

 sitized insects desired and deliver them at the laboratories. After 

 their habits and life histories are studied, numbers of them are packed 

 for shipment. They may be in the egg, larva, pupa, or adult stage 

 when sent, the stage preferred being determined by the knowledge 

 man has gained of the ways of the parasite and its host. Frequently 

 the parasite is a larva in the egg or other stage of the host, or in a 

 cocoon of its own, out of, or in, the hosts' body or cocoon. A conven- 

 ient time to send some parasites is in a cold season, when they are 

 naturally dormant due to low temperature, or if sent in a warm season 

 they have frequently been stored in refrigerators at temperatures of 

 40° to 50° F. on ship to prevent further development before they 

 reach their destination. Or food and hosts may be supplied in cages 

 to enable the parasite to continue its growth in a normal way in 

 transit. If the parasite larva be in the host when sent, it may reach 

 the pupa or even the adult state by the time it arrives after a journey 

 lasting from one to two weeks. 



If the parasites make the trip successfully, they arc next placed 

 in a laboratory to study further their habits, to determine whether 

 hyperparasites may be present, and to develop large numbers for 

 liberation. The breeding is done in many ways, depending again 

 on the species concerned, and a considerable variety of cages and 

 technique are employed. The hosts are provided in these cages to 

 allow the parasites to multiply upon them. Usually when thousands 

 are developed, they are taken, at the most opportune time known, to 

 selected spots where the host is abundant, and where the environment 

 is otherwise favorable to the survival of the parasite. Thereafter 

 the parasite is dependent entirely on its own persistence in finding 

 its hosts and in resisting the climate and other untoward influences. 

 Sometimes our own parasites attack it, even when its native enemies 

 have been left behind. Probably less than half the species intro- 

 duced from other countries are established, or, if established may 



