Abstract

A detailed study of the variations in the degree of insect damage under varying conditions may not only enable us to assess the value of the present state of knowledge in economic entomology, but also possibly enable us to get glimpses into new vistas of possibilities of pest-control. The rapid strides that are being made in plant-breeding to achieve results of economic importance may, for instance, lead to practical results if the entomologist were to indicate to the plant-breeder the lines on which he could help in the solution of problems of entomological interest. Wherever a large number of varieties of a crop is under experimenta- tion, one frequently notices much variation in the degree of insect attack. In certain cases, it may possibly be by chance that a particular variety consistently shows the same degree of damage. It is in gortant to ascer- tain whether the degree of infestation exhibited is really due to any definite. inherent characters by the careful elimination of external factors that some- times bring about insect attack. It is the object of this article to indicate briefly some of the external factors that have to be taken into consideration before one can assess the true value of the powers of resistance shown by any variety, and to examine some of the inherent characters to see how far they are helpful in the repellency of attack by insect pests. In this connec- tion it may be noted that it is no easy matter to compare varieties as regards their differences in the degree of susceptibility to insect attack, as the hatchlings do not usually confine themselves to the strips on which the eggs may happen to be laid, but get themselves distributed with little regard to the object of the observations in view.

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