INSECT PESTS OF OHIO SHADE AND FOREST TREES 225 



Natural enemies. — Unfavorable weather conditions in all like- 

 lihood constitute as effective a check on the species as any other 

 agency. If the weather suddenly turns cold, or if a heavy snow or 

 ice storm occurs at the time the brood is emerging, many are de- 

 stroyed. Moreover, it has been observed (11) that freezing weather 

 when the larvae are young kills many of them. 



Native birds are an important control agency. Forty-two 

 species of native birds feed upon these worms, according to Prof. 

 J. S. Hine of the Ohio State University (12). 



A considerable number of insects are known to prey upon and 

 parasitize cankerworms in their various stages. The predaceous 

 beetles and wasps, attacking adults and larvae, Ichneumonid and 

 Tachinid parasites attacking the larvae, and Chalcid parasites at- 

 tacking the eggs, all contribute in subduing outbreaks of the pest. 



Control. — Two methods of control are available. Since each 

 has its good and weak points, which depend much upon' the condi- 

 tions under which the cankerworm outbreak occurs, the selection 

 of the most suitable method depends upon the judgment of the 

 operator. 



In years past the control method most commonly recommended 

 has been banding the trees with some sticky substance, such as tree 

 tanglefoot as described on page 205. The object of banding was to 

 prevent the female cankerworm moths from ascending the trees 

 and depositing their eggs in the preferred situations. In theory 

 the idea works perfectly ; in practice it is found to have limitations. 

 Its greatest deficiency lies in the fact that the adult moths do not 

 all ascend the tree within a period of a few days, but that some of 

 the fall cankerworm adults may go up in the fall and deposit their 

 eggs while others may wait until spring, and during the spring the 

 emergence of both fall and spring moths may extend over a period 

 of several weeks. It will be seen, therefore, that in order to insure 

 success, the bands must be in place, and in working condition for 3 

 or 4 months. Cold weather and blowing dust and trash coat the 

 sticky-band surface, and unless the band is freshened, this permits 

 a safe passage of the insects over it. 



The second weakness of the method is that if the brood of 

 cankerworm moths is very heavy, and the sticky bands are not 

 inspected from day to day, the dead bodies of the captured moths 

 completely bridge the band and late-comers cross over in safety. 

 Such a band is illustrated in Plate XXVIII, Fig. 1. W .H. Goodwin 

 records having caught as many as fifteen thousand female canker- 

 worm moths on a single band, and when one considers the fact that 



