26 REPORT ON INJURIOUS INSECTS FOR 1907. 



These investigations are sufficiently important to reproduce in his 

 own words, he states " The presence of the aerial form of the woolly- 

 aphis is readily detected by the bluish-white cottony looking substance 

 that is excreted by and covers the greater part of each wingless 

 individual aphis ; and since these insects live in clusters or colonies, 

 the patches of white matter are very conspicuous, and can scarcely 

 escape the notice of even the most casual observer. It has been my 

 experience to find in nature this aerial form in Missouri only in rare 

 cases, and then only in those places where some injury had caused 

 an abrasion of the bark ; or some limb or twig had been cut or broken 

 off ; or where they had been crowded from the ground up to the base 

 of the trunk ; or on the suckers that had been allowed to grow around 

 the tree. They are frequently artificially induced to attack the trunk 

 by mulching, or by using wrappers around the base of the tree as a 

 protection against borers and rabbits. But whatever may be the cause 

 of their presence above the ground, the result is the same, namely ; 

 to cause an abnormal growth of the infested portion, resulting in the 

 formation of a rough and pitted surface, and at times causing the death 

 of the limb at the point infested. Ho\vever, this injury is so slight in 

 this state that it is insignificant in comparison with that found in the 

 northern and eastern states, and especially in Europe, where apple 

 trees are frequently killed outright by this aerial form. 



The presence of the root inhabiting form is readily detected by 

 removing the earth from the roots near the trunk of the infested tree. 

 The appearance of a bluish-white cottony or mildew looking substance, 

 or of knotty and distorted roots, will indicate its presence. It is this 

 root or subterranean form that causes so much damage to the apple 

 orchards in the southern half of Missouri, and to apple nursery stock 

 throughout the state. The infested apple tree appears sickly ; it does 

 not grow as it should ; its leaves are less numerous and they have 

 more of a pale green or yellowish color than is natural ; and finally 

 the tree dies outright or is blown over with the first slight wind. 

 Such are the outward indications that a tree is badly infested with 

 this pest. Sometimes the tree blows over with a heavy wind without 

 showing these outward appearances in so marked a degree ; but one 

 soon becomes familiar with the appearance of infested trees, and can 

 readily locate them before they are past recovery. In orchards, it 

 appears that the great bulk of the damage from this pest comes 

 directly from the fact that the trees blow over so easily, the roots 

 breaking off close to the trunk. Of course this is due to the fact 

 that the roots have decayed ; and I am fully convinced from actual 

 observation that ninety-five per cent of the cases of so-called u root-rot " 

 in apple trees in this state is in reality the result of the attack of the 

 woolly-aphis. In nursery stock, the damage comes directly from the 



