64 DISEASES OF CROPS. 



already described. The Aphidce, or plant-lice, are an ex- 

 cessively injurious family of Homopterous insects. Every 

 farmer, every rose cultivator, every hop-grower has too 

 great reason to be well acquainted with these destructive 

 pests. The species are very numerous, almost every plant 

 having its own peculiar parasite ; they attack the leaves, 

 stems, shoots, and even the roots of plants, piercing with 

 their sharp proboscis the cuticles and sucking the juices. 

 Aphis rapce is chiefly found on the under surfaces of 

 turnip leaves. The wingless female (viviparous) is green, 

 but becomes a yellowish-red colour later in the season. 

 The head and thorax of the winged female are black, 

 whilst the abdomen and wings are of a yellow colour. 

 The posterior part of the abdomen of this species is flask- 

 shaped (Fig. 27 E). According to Curtis, the variety 

 known as Aphis floris-rapce (Fig. 27 A and C) is found on 

 the flower-stalks. Aphis rapm " multiplies with amazing 

 rapidity under favourable atmospheric conditions." 



The great enemies of the Aphidce are the so-called 

 " lady-birds " — small beetles belonging to the Cocci- 

 nellidm. The French call these insects " Bete de la 

 Vierge " and " Vache a Dieu." The Germans caU them 

 "Marienkafer," " Marienkuh," and " Gotteslammchen." 

 The majority of these insects are undoubtedly the friends 

 of the farmer, and their presence upon all caltivated plants 

 is most beneficial. The " common," or seven-spotted lady- 

 bird {Coccinella septempunctata), and the two-spotted 

 lady-bird (C. bipunctata) are common species. " They lay 

 their eggs in small patches in the midst of the Aphides 

 which are destined to furnish nourishment to the larvae." 



Prevention and Cure. — (1) "Nearly all the remedies 

 proposed for the extermination of Aphis rapce consist of 

 water containing some poisonous infusion, such as tobacco, 



