PARASITES IN INSEC? CONTROL—HOWARD 417 
ing parasites of an important imported pest, only to lose the results 
of this costly and laborious journey through inadequate provision 
and care at the home end. 
Great ingenuity has been exercised in the multiplication of para- 
sites at the importing end. The development of the potato sprout 
idea for the rapid rearing of mealybugs to serve as food for 
Cryptolaemus in confinement in California laboratories is a marked 
example, and other novel and effective methods have been worked 
out at Melrose Highlands, at Riverton, and in France. And a better 
and most varied technique will be developed as time goes on. 
The latest attempt to sum up the complications and the difficul- 
ties in parasite introduction has been made by Dr. B. Trouvelot 
ot Doctor Marchal’s laboratory, in a paper to which we have already 
referred. He brings out in clear form many of the points that 
had already occurred to most of us engaged in active work of this 
kind and summarizes in a concise way the factors that should be 
comparatively studied both in the importing and exporting coun- 
tries. These, he thinks, are (1) the climate (humidity or drought) 
of certain months modifying both the activities of the species 
and their rapidity of multiplication; (2) the distribution of plants, 
both wild and cultivated; (3) the fauna, its composition and dis- 
tribution; (4) the cultural methods followed (the size of the fields, 
character of the soil, period of harvest, and the amount of cul- 
tivation); (5) finally a factor dependent upon all of the others— 
the life history of the host, its local and regional distribution and 
its vulnerability. 
After general consideration has been given to the points specified 
above, Trouvelot again considers other points which must be studied 
before a choice of parasites can be gained. These may be listed as 
follows: 
(1) Synchronism of the life round between the parasite and the 
host. 
(2) Parasite activity. 
(3) Possibility of superparasitism and coparasitism. 
(4) Tendency to hyperparasitism. 
(5) Variations of the parasitic activity according to the climate. 
(6) Possibilities of hybridization with related species belonging 
to the importing country. 
(7) Power of dispersal of the parasites compared with that of 
the host. 
We have already hinted at the popular appeal which parasite work 
always carries. Last September there were two striking instances 
of this. There was a conference of State experiment station direc- 
tors and agricultural officials in Ohio, Michigan, and southern Onta- 
