1919 ENTOMOLOGICAL SOCIETY. 31 



even on a relatively younger shoot but it is utterly impossible to raise winged 

 Myzus persicue on a similar host without the application of a wing developing 

 substance." The writer has reared very large numbers of persicae on just such 

 an host without the application of any such substance, and has repeatedly obtained 

 90 to 100 per cent, winged. But this was where winged forms would be expected 

 in the line in large numbers. 



The peculiar life histories of members of this superfamily have led to studies 

 on the predetermination of sex. Morgan,^ for example, has shown that in 

 Phylloxera caryaecaulis there are two types of males depending on the fate of 

 one of the small sex chromosomes when the polar body is about to be produced. 

 Each of these males thus produces a different -type of spermatozoon, one female 

 producing and one male producing. If the sexual egg is fertilized by the female 

 producing spermatozoon the resulting stem mother will give rise to the line which 

 results in the sexual female. If it is fertilized by the male producing spermatozoon 

 the resulting stem mother will give rise to a line which results in the production 

 of the male. It is thus seen why we have two types of stem mothers, one giving 

 the large Qg^ migrants and the other small egg migrants. 



The production of plant galls by aphids has given rise to studies on these 

 modifications of plant tissues and attempts to determine the factors at work. In 

 some instances it has been claimed that the agent might be an enzyme present 

 in the saliva for in such galls as those of Eriosoma lanigera the normal starch 

 is replaced by sugar. The gall makers, too, have led to observations on the sensory 

 organs of aphids. Those species which inhabit galls as w6ll as many of the 

 subterranean species have larger and more .prominent sensoria on the antennae 

 than have other species. These are in striking contrast to the sensoria on the 

 antennae of the solitary land free-living forms. The gall formers and subterranean 

 forms also have a larger number of Hicks organs or olfactory pores on the wings 

 than do the solitary species. 



Much interesting work has been done on the relation between aphids and 

 their parasites, both animal and plant, and their predators. It is claimed by 

 some workers that certain lower forms are associated with aphids in a commcn- 

 salistic relationship' and may be even passed from one generation to the next 

 through the egg. Many of the parasites so reduce the numbers of aphids that a 

 species otherwise very destructive need scarcely be considered. 



Finally certain aphids are among the most injurious species of insects with 

 which the farmer has to deal. The woolly apple aphis for example, had become 

 so important even in 1832 that the Academic de Eouen offered a gold medal for 

 the working out of its life history. The outbreaks of Toxoptera graminum in 

 the grain growing areas of the world have done enormous damage and it is only 

 necessary to watch the exchanges to see the influence this one insect sometimes 

 has in the business world. In one outbreak according to Eondani the swarms 

 of aphids appeared like dark clouds and later their dead bodies covered all the 

 streets of the city. 



It is thus seen that aphids have a very vital human interest. They supply 

 materials worth much to the arts. They furnish certain quantities of food. 

 And they have given the clews which have resulted in the working out of im- 

 portant biological problems. On the other hand they contribute some of our 

 worst enemies of agriculture. But in our fight against these species we arc 

 aided by natural factors without which many of our important crops would 1)0 

 impossible. 



'Morgan, T. H.— Journ. Exp. Zool., XTX, No. 3. 1915. 



