133 



and not being able to survive unless it finds a parasite larva in 

 which to live. 



Another place where a study of the interrelation of parasite 

 and host are being minutely studied is at the laboratory of the 

 Agricultural School at Portici, Italy. Many new and interesting 

 habits are being brought to light. Dr. Silvestri, at this place, 

 has made some most minute investigations of polyembryony. 

 Polyembryony is that method of development by which a large 

 number of embryos is produced from one egg, as occurs with 

 some of the Chalcididae. Dr. Silvestri investigated this phe- 

 nomonon with Litomstix, a parasite of Plusia, and a number of 

 other moths. According to his investigations, the process of de- 

 velopment is as follows : the adult female parasite deposites one 

 egg in an egg of the moth. It does not destroy the egg as egg- 

 parasites do. It does not interfere with the embryonal develop- 

 ment of the host nor the hatching of the caterpillar, nor does 

 it prevent the latter growing to its full size ; on the contrary, a 

 parasitized caterpillar attains a somewhat larger growth than a 

 normal healthy one. Returning to the egg of the parasite, a 

 peculiar nuclear division takes place in its development, which 

 results in a segmentation different from usual, by which, event- 

 ually, a large number of minute embryos is formed from this 

 one egg. These embryos then feed and grow in the growing 

 caterpillar, not killing it till after it has Decome full-grown and 

 spun its cocoon ; when they soon finish their growth, having 

 eaten the entire contents of the caterpillar skin which they en- 

 tirely fill, giving it the appearance of being crammed full and 

 stretched beyonu (..ic normal size. These parasite larvae pupate 

 in this position, and in due time the adults emerge to the num- 

 ber of several hundred, even thousands. As high as 3000 has 

 been reported as produced in this way in one caterpillar, and all 

 having originated from a single egg. This method of develop- 

 ment is known for a number of parasites. We have in the Ha- 

 waiian Islands a parasite on native wasps which probably re- 

 produces in this way, though the details of it have not been 

 worked out for this species. 



Some mention should be made of the investigation of para- 

 sites in connection with the cotton doII weevil in the Southern 

 States. No parasites have been obtained from foreign coun- 

 tries, but in the study of the native parasites, 26 species have 

 been found attacking the boll weevil. These sometimes have 

 l)een found killing quite a good percentage of the weevils, and 

 thus becoming one of the important factors in their control, in 

 1909, producing an average destruction of i6 per cent. A good 

 deal of work has been carried on in distributing the more effi- 

 cient of these parasites from one place to another in Texas, and 

 also to those places in Louisiana and Mississippi to which the 

 Aveevil has spread. 



Considerable experimenting has also been done in the transfer 



