Chapter 16. 
INJURIOUS ANIMALS (Continued). 
Aphides and their life-histories; preventive and remedial 
measures. The Apple Sucker. Scale Insects. Greénhouse 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. The 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.” This accumulates on the leaves, 
blocking up their stomata, and also provides nutriment 
upon which 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. 
After a variable number of generations of this kind, 
winged males and winged females become evident, and 
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