Chapter 16. 



INJURIOUS ANIMALS (Continued). 



Aphides and their life-histories ; preventive and remedial 

 measures. The Apple Sucker, Scale Insects. Greenhouse Pests 

 and Fumigation Methods. 



The present lecture is devoted to a consideration of 

 certain injurious Hemiptera. Members of this order of 

 Insects are characterised by the presence of a jointed 

 rostrum or beak, enclosing two pairs of stylets used for 

 piercing the tissues of plants and imbibing sap therefrom. 

 Nearly always four wings are present, the young re- 

 semble the adults in general form, and a pupa stage is 

 almost always absent, l^he family of the Aphididae is 

 of great importance, including as it does the " Green Fly " 

 or " Plant Lice.'' Aphides may draw the sap from all 

 parts of plants, even the roots, and the injuries they 

 cause are often great. They bear near the end of the 

 body a pair of tubes, which secrete a substance commonly 

 termed '"honey dew." Ihis accumulates on the leaves, 

 blocking up their stomata, and also provides nutriment 

 upon w^hich various Fungi develop. Aphides undergo a 

 remarkable life cycle. In the autumn we usually find 

 the fertilised winged females. The eggs laid by them 

 develop the following spring into wingless females. 

 These latter breed with great rapidity by parthenogenesis 

 — I.e., without the agency of the males, none being 

 present. Eggs are not laid but living young are brought 

 forth, and this goes on for several generations until the 

 .summer. Winged females then appear but there are still 

 no males, and living young continue to be produced. 

 Aiter a variable number of generations of this kind, 

 winged males and winged females become evident, and 



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