356 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 2 



istic tendencies, whereas others are very tolerant, and consequently 

 are dominated and destroyed by the more active ones. Where two 

 tolerant species occur together in the same host one or both may die 

 from starvation, though occasionally it has been seen that both 

 species develop and mature normally. 



The rate of increase of insect parasites, or, rather, their capacity 

 for reproduction, is dependent upon the manner of parasitization 

 of the host and the hazards which are encountered during the period 

 of development. Certain of these species ma}^ deposit 10,000 or more 

 eggs and still show no increase in numbers from j^ear to year. These 

 species are the ones which do not lay their eggs directly upon or in 

 the host, but instead scatter them promiscuously or place them only 

 in the general vicinity of the host. The young larva then has the 

 task of finding and entering its host, and the number which are able 

 to do so is dependent upon the abundance of the latter. These mi- 

 nute larvae usually have a considerable power of search, though their 

 range is limited. The larvae of Perilampus, which is one-twentieth 

 of an inch in length, moves in a looping manner and the total 

 distance it is able to travel during its life is consequently limited. 

 The similar larvae of certain other wasps and flies are aided by an 

 ability to jump considerable distances, and in this way they are 

 often able to reach a host larva in their vicinity. 



The ant parasites of the hymenopterous family Eucharidae, which 

 develop upon pupae in the nest, deposit from 1,000 to 10,000 eggs 

 and have a very unusual mode of life. In Schizaspidia the eggs are 

 not laid in the nest at all, but are placed in large masses in the buds 

 of trees. Here they pass the winter and hatch the following spring, 

 shortly after the buds expand. At this time of the year the aphids 

 are quite numerous on the foliage and the worker ants congregate 

 about them to feed on the honeydew which they secrete. The young 

 larvae of Schizasjoidia are at this time resting on the leaves, and 

 whenever opportunity offers attach themselves to the ants and are 

 eventually carried down into the nest. Here they transfer to the 

 mature larvae and eventually complete their development upon the 

 pupae. In one single small mulberry tree which was examined, there 

 were estimated to be at least 6,000,000 eggs of this species within 

 the buds at the time of the examination. Tliis proved to be a more 

 or less constant condition each year. The ant population in the vicin- 

 ity totaled only a few thousand, yet only about 50 per cent were 

 destroyed by the parasite. The number of larvae which are able to 

 attach themselves to the worker ants must be exceedingly small. 

 They are entirely dependent upon the aphids to attract the ants to 

 the tree, and if these aphids are scarce, then the chance of the para- 

 site finally reaching an ant nest becomes exceedingly small, for only 

 an occasional ant will be found upon the tree. 



