316 INSECTS AND MAN 



latter feature necessitated the presence of living Aleyrodes 

 throughout the journey, so that the parasites at the time 

 of their emergence would have material upon which to 

 work." Young infested citrus-trees could nowhere be 

 found, so a number of young healthy trees were dug up, 

 placed in pots, and, as the white fly prefers tender growth 

 for oviposition, cultural methods were enforced to induce 

 the trees to send out new shoots. No sooner, however, did 

 the desired growth appear than it was attacked by a 

 lepidopterous leaf miner, Phyllocnistis citrella, and a bud 

 worm, Agonopteryx sp., and their combined attacks rendered 

 the trees useless for the purpose for which they were 

 required. A second set of potted trees was accordingly 

 grown in large cloth cages, to protect them from extraneous 

 insect pests, and these were successfully infested with 

 white fly and its hymenopterous parasites. 



En passant, it may be mentioned that the parasite prefers 

 the larval stages of its host, but will, on occasion, oviposit 

 in the pupa. Whether larvae or pupa, the parasitised 

 individuals are much thicker and more opaque than healthy 

 ones, thus becoming more easily recognised. With a lens 

 the whitish parasite larvae can be seen within the white fly 

 host. The pupal stage of the parasite is almost black, a 

 fact which causes the parasitised white flies containing 

 pupa cases to appear very dark. On attaining maturity 

 the parasite eats a small hole in the back of its host, and 

 through the opening emerges into the open air. 



About the middle of October appeared a favourable time 

 for shipment of the parasites to America, accordingly 

 Wardian cases were made for their transport. These cases 

 are specially constructed for the transportation of tender 

 plants over long distances; each case resembles a green- 

 house on a small scale, and is perfectly air-tight, except for 

 two small holes at the top for ventilation ; plants can travel 

 in them for long distances without watering. Five cases, each 

 containing between ten and twenty young citrus-trees, were 



