268 THE PRACTICAL APPLICATION OF ECOLOGY 



the nutrition of a given crop in relation to its susceptibility to 

 insect attack is one in which the entomologist becomes largely 

 dependent upon knowledge derived from other sciences. The 

 nutritional requirements of different crops form in themselves a 

 specialised branch of plant physiology, and they are intimately 

 associated with questions of soil conditions, rainfall, and other 

 factors. Recent research is bringing to light evidence which 

 points to the conclusion that excess or deficiency of certain food- 

 materials required by the plant betrays itself in the response the 

 plant exercises towards insect injury. Similarly, particular soil 

 conditions in some cases appear to conduce to heavier damage 

 resulting from insect attacks than when plants are grown under 

 different conditions. The future is likely to see increasing 

 attention being given to the cultural conditions under which 

 certain crops, particularly liable to insect infestation, are grown. 

 The possibility is, therefore, opening out of ensuring a measure of 

 insect control by regulating the nutrition of crops in such a way 

 that they become less liable to suffer severe injuries. 



1. The problem of froghopper ^ damage to sugar cane in 

 Trinidad has become more one for the plant physiologist and the 

 agricultural specialist than for the entomologist. The injuries 

 caused by the sucking propensities of the insect appear to be 

 intimately connected with the internal physiological condition of 

 the cane ; the crop does not necessarily suffer the greatest damage 

 when the froghoppers have been most numerous in attack. The 

 important observation that there is a marked difference in the 

 degree of attack resulting on cane growing in red acid soil and that 

 growing in alkaline black-marl soil in certain localities, ^ in that the 

 former suffers severe injury whilst the latter does not, has opened 

 up the whole question of the nutrition of the cane-plant in this 

 connection. It was found that a positive correlation prevails 

 between the degree of saturation of soils with lime and cane 

 susceptibility. It appears that soils of areas free from severe 

 injury by the froghopper are absorbtively saturated by lime, and 



1 The species involved is Monecphora (Tomaspis) saccharina, family 

 Cercopidae. 



2 The greatest number of eggs also appears to be laid in heavy acid soils, 

 and the fewest in black marl soil. 



