INSECTS AND FUNGI 



By T. PETCH, B.Sc, B.A. 

 Mycologist to the Government of Ceylon 



The long processions of ants bearing pieces cut from living 

 leaves early attracted the attention of all naturalists who visited 

 South America. These leaf fragments are taken into the nest, 

 and are there used as a substratum for the cultivation of a 

 particular species of fungus which forms the insects' normal 

 food. The question as to their use was raised by Bates in 

 his Naturalist on the Amazon. Belt {The Naturalist in Nicaragua) 

 suggested that the ants were " mushroom growers and eaters " ; 

 and the relationship was worked out in detail by A. Moller 

 about fifteen years ago. 



Moller found that the pieces of leaves are cut into small 

 fragments and formed into balls, which are packed in a spongy 

 mass in the nest. Over and through the comb thus made 

 runs the mycelium of a fungus which binds it together. This 

 mycelium bears small tufts of hyphae with swollen tips — the 

 " kohlrabi " heads — which furnish a supply of food in a more 

 concentrated form than would the normal hyphae. No other 

 fungus is found in the nest — a fact which makes it evident 

 that intruding species are systematically weeded out. The 

 mycelium bearing the kohlrabi heads was proved to be that 

 of an agaric, Pholiota gongylophora, which sometimes grows 

 from the fungus garden and appears on the top of the nest ; 

 and it has been generally assumed that the production of 

 these heads is due to " selection " exercised by the insects. 

 The shape of the swollen hypha ends varies in the nests of 

 different species, and the agaric has only been discovered in 

 the case of one of these ; but Moller believes that the fungus 

 is the same in all cases, and that the differences observed in 

 the kohlrabi heads are to be explained by differences in the 

 degree of specialisation to which the mycelium has been 

 developed by the insects. When the ants are removed from 

 the nest, the fungus garden develops two forms of mycelia, 



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