162 MICROSCOPIC ANIMAL FORMS AS ANTAGONISTS 



RELATION OF NEMATODES TO SOIL 

 MICROORGANISMS 



Nematode worms are represented in the soil by a number of sapro- 

 phytes as well as by many plant and animal parasites. The latter vary 

 greatly in their relation to the host. The larvae of the cereal parasite 

 Tylenchus tritici penetrate the wheat seedlings between the leaf 

 sheaths, near the growing or apical points. When the head is formed, 

 the larvae enter the flowering parts and form galls. They become sexu- 

 ally mature, mate, and lay eggs which hatch in the galls, and then be- 

 come dormant. When the galls fall to the ground and decompose, the 

 larvae are liberated and proceed to find and attack new plants. Other 

 nematodes attack plants by feeding upon the roots. The methods of 

 control require, therefore, a knowledge of their life history. Some 

 species produce resistant forms or cysts that may survive in the soil for 

 many years, even in the absence of the host plant. Soil sterilization by 

 steam or by chemicals is frequently employed as a measure of nematode 

 extermination. 



Antagonistic relationships may be utilized for the control of nema- 

 todes. Linford et al. (572) found that the root-knot nematode of pine- 

 apple {Heterodera marioni) may be controlled by heavy applications of 

 organic material. The decomposition of this material results in a greatly 

 increased population of saprophytic nematodes in the soil. The decom- 

 posed organic residues also support large numbers of such other soil 

 microorganisms destructive to the parasitic nematodes as the nema- 

 capturing fungi (180, 196), the nontrapping fungal parasites, the 

 predaceous nematodes, the predaceous mites, and different bacteria ca- 

 pable of destroying nematodes. 



BACTERICIDAL ACTION OF MAGGOTS 



Surgical maggots are said to have a bactericidal effect in wounds, in 

 addition to removing necrotic debris. The presence of an active bacteri- 

 cidal substance which is thermostable and active against 5. aureus^ 

 hemolytic streptococci, and CI. welchii has been demonstrated (854) in 

 the maggot LuciUa serkata. 



