COOPERATION 155 



are those in which insects that excrete "honey dew," such as plant 

 lice, mealy bugs, and scale insects, are attended by ants or by beetles 

 such as the silvanids. These gather the sweet excrement as it falls 

 on the leaves of the host plant or take it directly from the bodies as 

 it is made. Some species of ants have developed the habit of stroking 

 individuals of the phytophthora to cause them to excrete more liquid. 

 JNIoreover, they conserve and increase the supply of this food by pro- 

 tecting the producers from marauding enemies, caring for them in 

 special shelters, gathering and distributing the eggs, and transport- 

 ing the adults to their proper host plants (Wheeler, 1923:178,31). 



Cooperation in Plant-animal Colonies. The simplest cooperation 

 in such colonies is found both in water and in soils that contain algae. 

 The carbon dioxide required by the algae for photosynthesis is sup- 

 plied in large measure by the animals, and in turn the algae give off 

 oxygen for animal respiration. The waste products of the animals as 

 well as the dead bodies are broken down by bacteria and the simple 

 materials elaborated to the point where they can be utilized by the 

 algae. A specific example of such a relation at or near the surface 

 is furnished by Nostoc and Azotobacter. 



A much more striking behavior cooperation exists between several 

 groups of insects and the fungi they cultivate for food when setting 

 up new colonies and entering new areas. Such a symbiotic relation is 

 exhibited by beetles, ants, and termites, the general features being 

 more or less similar for the three groups. The ''ambrosia" beetles 

 tunnel in twigs or wood, placing the eggs singly in pits and then filling 

 these with chips and mycelium, which is renewed by the mother from 

 time to time. She also clears the refuse away from the pits, and this 

 is utilized for further development of mycelium. When the female 

 leaves her pit, she carries conidia of the particular species of hypho- 

 mycete to her new home. Though there is considerable choice in the 

 selection of a nesting site, each species of beetle makes use of a par- 

 ticular species of mold. 



By comparison, the fungous gardens of the ants and termites are 

 huge affairs, in keeping with their large compounds, but the members 

 of these two groups are in accord with the ambrosia beetles in selecting 

 a single species of fungus for culture. The ants are known to use the 

 mycelium of agarics, polypores, and black fungi, while the first and 

 last have been found in the cultures of termites. The higher genera 

 of ants cut segments from leaves and carry them to the nest to be 

 comminuted and made into a medium for growing the mycelium. The 

 hyphal threads are manipulated by specialized workers in such fashion 

 as to produce swellings or bromatia, which serve as food for both 



