INSECT CONTROL 309 



as a beneficial insect its slow rate of dispersion, and the 

 fact that, owing to physical limitations, it can only para- 

 sitise the uppermost layer of eggs in each egg mass, leaving 

 the second and third layers untouched. 



Like the insect just mentioned, Schedius kuvance (fig. 98) 

 is a minute Hymenopteron ; like Anastatus, too, it attacks 

 the same host and is also physically incapable of oviposit- 

 ing in any but the top layer of eggs in a mass. In other 

 respects the two insects differ. Anastatus is a true egg 

 parasite, Schedius is an internal parasite of the unhatched 

 caterpillar. Again, Anastatus is responsible for one genera- 

 tion annually, and its seasonal history is correlated with 

 that of its host. Schedius, on the contrary, passes through a 

 generation a month, under suitable climatic conditions, and 

 probably an alternate host is necessary, to carry it through 

 the period, after the gipsy moth eggs have hatched in the 

 spring and before the moths begin depositing eggs for a 

 new generation. It was not till 1909 that a successful im- 

 portation of the parasite from Japan was accomplished, the 

 eleven individuals which then reached America were the 

 progenitors of a numerous and prolific race. 



The first Schedius ever raised in America was a single 

 male, in 1908, which died before a mate could be provided 

 for it. Shortly afterwards a single female was raised, she 

 oviposited in gipsy moth eggs, and her offspring amounted 

 to twenty- eight parthenogenic males, i.e. produced without 

 previous mating of the two sexes. In the hope that this 

 single female might be fertilised and produce females for 

 the furtherance of the race, she was confined with some of 

 her asexually produced sons, but she had evidently laid 

 her full complement of eggs, at any rate she died without 

 further oviposition. A few months later a somewhat 

 similar experiment was tried ; but in this case, after the 

 female had deposited a few eggs she was put into cold 

 storage to await events. As before, the parthenogenic 

 young were all males ; when they had emerged the female 



