1 904-] 



Aphides or Plant-Lice. 



35 



They damage plants in a twofold manner, first by sucking 

 out the sap and so weakening the vitality of the plant, and 

 secondly by stopping the respiration of the plant by blocking 

 up the stomata (or breathing pores) of the leaves with their 

 excreta. This excreta is not only of the ordinary kind, but 

 also consists of a sweet gummy substance that stops the 

 " breathing " of the plant, and is called " honey-dew." This 

 substance is passed out through two tubes, called " cornicles," 

 situated on the back of the Aphides. A few Aphides, such as 

 the Woolly Aphis (Leaflet No. 34), have no cornicles and 

 produce no honey-dew. The skin of the plant-lice is provided 

 with numerous glands which secrete either a waxy substance 

 that covers the skin (Rose Aphis, Bean Aphis, &c.) or dense 

 woolly masses (Beech Aphis, Woolly Aphis, &c). In both cases 

 the excreted substances have the power of throwing off water 

 and so of keeping the insects dry. 



Life History. 



Aphides may be winged or they may be wingless ; as a rule 

 winged and wingless generations occur in each species. 



The reproduction in Aphides is very rapid. They not only 

 breed in the ordinary way, but they can also breed without any 

 males being present. Some Aphides live only on one kind of 

 plant, the Rose Aphis {Sifihouophora roses) for instance ; others 

 live on two plants, migrating from one to the other, as the Hop 

 Aphis {Phorodon humuli) which migrates between the hops 

 and the prunes {vide Leaflet No. 88) ; others live on several 

 plants, as the Bean Aphis {Aphis rumicis), which may be found 

 on Beans, Peas, Docks, and Furze. 



Some kinds, as the Rose Aphis, attack leafage and shoots 

 alike; others, as the Bean Aphis, may even attack the 'fruit 

 (pods) ; others the stem and twigs (Woolly Aphis). Not only 

 do plant-lice migrate from plant to plant, but some can live 

 both above and below ground, and may migrate from root to 

 trunk or root to foliage (as the Phylloxera of the Vine and the 

 Woolly Aphis of the Apple). 



The typical life-history of the Aphis is as follows : — The 

 adult female or " Mother Queen " is wingless, and produces, 

 without the agency of a male, not eggs, but living young ; these 



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