Aphis rumicis on the Mangel-Wurzel in Shropshire. 3 



autumn contained a crop of mangels and a crop of swedes ; 

 the former phants were covered with the conspicuous black 

 ^;:>A«6'-population, but the swedes were not attacked at all ; 

 even the row adjacent to the infected mangels was free from 

 them. Ajyhis hrassicm occurred, but not A. rumicis. This 

 fact would lead one to believe that the Aphis prefers mangels 

 to swedes, and that probably it has a predilection for plants 

 either of the same species or belonging to the same natural 

 order. In the absence of an abundant supply of their favourite 

 food the insects take to other food-plants readily accessible. 

 The question of its almost omnivorous habits may be to some 

 extent determined by the absence of its favourite food from 

 certain localities. 



The affected leaves presented on their under surfaces large 

 black masses of Aphis-Wh^ almost every leaf of the plant was 

 sometimes covered, the result being that the whole showed a 

 sickly yellow hue, the underside of the leaves being deeply 

 puckered and distorted ; after a time the leaves drooped and 

 withered. For some time the damage continued, the apterous 

 viviparous females being excessively prolific and producing 

 their young larvai in prodigious numbers. I have counted as 

 many as thirty larvae in various stages of development in a 

 single individual. One might occasionally see amongst these 

 black Aphis masses some dried-up skins of the insect, the 

 result of ichneumon-parasitism ; but, on the whole, no marked 

 beneficial result from insect-agency was apparent, and one 

 began to fear for the mangel crops. Fortunately, however, 

 an effective aid suddenly came to the rescue in the presence 

 of a microscopic fungus of some kind which completely 

 covered the Aphides. About the beginning of October I 

 noticed that these black ^^;»A?s-patches on the leaves contained 

 a number of red or rust-coloured spots, which proved to be 

 Aphides either in a moribund or dead state. The microscope 

 revealed the presence of some fungus, which it was quite 

 clear was plying its beneficial destructive agency most 

 vigorously on the Ajjh is- gxow^^. 



I placed some infected aphides under a glass with healthy 

 specimens from my garden-beans, and in a short time 

 these became similarly covered with the same red-coloured 

 fungoid growth. The niggers took the scarlet fever and 

 died. On submitting this fungoid growth to the microscope, 

 I could detect numerous conidia amongst the filaments, but 

 could not quite satisfy myself as to their origin and mode of 

 attachment. About the end of October another phenomenon 

 presented itself: the red aphides turned a dull green both 

 on the plants in the fields and on the leaves I had under 



1* 



