340 TEXTBOOK OF ZOOLOGY 



bugs are kept as guests for the droplets of lioneydew which they 

 excrete when stroked by the antennae of the symbiont. Dr. S. A. 

 Forbes has reported most interestingly upon the activitiv'^s of the 

 cornroot aphid, Aphis maidi-radids Forbes and the brown ant, Lasius 

 niger var. americanus Emery. The little ants gather the aphid eggs 

 in October and take care of them during the winter. In the spring 

 before the com commences to grow, the aphids, after hatching, are 

 placed upon the roots of smartweed and some of the grasses. As soon 

 as the corn has started to grow the agamic female aphids are trans- 

 ferred onto the roots. Here many generations are produced par- 

 thenogenetically. Then in later September or October wingless males 

 and females are produced. After mating, eggs are laid, which are 

 gathered and stored for the winter by the ants. The ants are repaid 

 for the care they bestow on the aphids by receiving a honeydew given 

 off by the aphids, which they greedily feed upon. 



Many of the insect guests are beetles, Histeridae, Staphylinidae, 

 Pselaphidae, and Scarabaeidae. The two histerids, Hetaerms tristri- 

 atus Horn and H. zelus Fall are fairly common in ant nests in the 

 states west of the Rocky Mountains. Several species of Xenodusa, 

 members of the family Staphylinidae, are found in ant hills in the 

 United States and Mexico. A number of species of Batrisodes and 

 Reichenl)achia, pselaphids, and Cremastocheilus angularis LeC. and 

 C. KnocJii LeC, scarabaeids, are found in the colonies of several of 

 the mound ants. Some Diptera are also guests in ant colonies. 



ECONOMIC RELATIONS 



Insects attack all kinds of growing crops and plants. The de- 

 struction of plants and their products valuable to man amounts to 

 over a billion dollars annually. This great loss goes on because 

 of the unabated and persistent struggle of the insects to maintain 

 their "place in the sun." Plants are not only eaten and damaged 

 by insects, but many plant diseases are spread by them. 



Animals and man suffer greatly from the attacks of insects. Many 

 species live as endoparasites or ectoparasites on animals and man, 

 and in so doing also spread disease. Some of the most dreaded 

 diseases known to man are carried by insects. Because of this there 

 has recently developed a new branch of entomology known as 

 "medical entomology." Some of the most notable progress during 



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