﻿ON ECONOMIC ENTOMOLOGY. 351 



parthenogenetic in spring or summer, and then non-sexual propagation gives way to 

 sexual. Hence to speak of a physiology of the seasons is perhaps not so unjustified 

 as it may appear. Who can doubt that the numerous species of insects which 

 live and thrive on plants, in particular plant-lice, are vitally affected by the 

 changes which autumn effects in plants. 2 The plant organism and its contents 

 such as starch, sugar, albumen and enzymes differ greatly during the summer, 

 autumn and winter seasons, and it is quite unthinkable that such material changes 

 should be without effect upon the state of all the insects which feed upon them. 



There is another problem which must prove highly interesting in relation to 

 applied Entomology ; I mean the question of the determination of sex, which at 

 present stands in the fore-front of biological research. And we see here 

 plainly how intimately physiological and applied science are interwoven. Both, 

 after all, occupy themselves with and revolve round cardinal questions of Life. 

 Landois 26 reared caterpillars on both plentiful and scanty food and as the 

 result of his observations concluded that plentiful feeding produced females and 

 scanty food males. According to Seitz, 33 Treat and Th. Gentry support that view. 

 But they have all clearly overlooked the fact that the sexes of insects are already 

 fixed very early, indeed long before they are capable of taking any food whatso- 

 ever. Standfuss 34 interprets the matter by pointing out that male caterpillars 

 are better able to survive bad nourishment than females ; hence that in the end 

 more males survive. One may also connect herewith the observation that 

 the proportion of sexes can change in so far that when a great invasion is 

 decreasing, the males are much more numerous than when the invasion was at its 

 height. This may be the result of the bad condition of the food-plants, or it 

 may more likely be due to changes in the organism. For we find ourselves here 

 facing only the external signs of the main causes of the difference of the sexes, 

 the real nature of which is still unknown to us. 



The physiological effects of insecticides. 



We are rather ignorant yet regarding the physiological processes which go on 

 in the bodies of insects in consequence of insecticides ; and although new 

 insecticides continue to be placed on the market and are being used, the question 

 of their physiological effect is rarely asked, far less has it been satisfactorily 

 answered. Pharmacology as an integral part of Insect Pest Research does 

 not yet exist ! Vague definitions of " stomach " or " contact " poisons are 

 doing service instead. Probably few of those who have used hydrocyanic acid 

 for the destruction of insect pests have been aware of the physiological effect 

 of that poison on the animal organism. CI. Bernard has observed that on 

 injecting hydrocyanic acid into the blood-vessels of mammalia a flow of red, 

 arterial blood issued from the veins. Geppert 22 followed up this observation 

 and found that by injecting hydrocyanic acid into blood-vessels the tissues of 

 the body lose their faculty for absorbing oxygen, hence the animal dies of 

 suffocation, in spite of abundance of aerial oxygen. For more than 12 years I 

 have occupied myself with this question and at the International Congress of 

 Agriculture in Paris (1900), Section for Plant Pathology, 8, 10 I stated that 

 caterpillars cannot fully develop in an atmosphere charged with hydrocyanic acid. 



