24 



THE PRINCIPAL NATURAL ENEMIES OF THE SPRUCE-DESTROYING 



BEETLE. 



Among a number of insect enemies of the different stages of the 

 beetle at least two are worthy of special mention — one a true parasite, 

 the other a predaceous enemy. 



A PARASITIC INSECT. 



The commonest parasite of the larvae is a small four-winged wasp- 

 like insect belonging to the order Hymenoptera, family Braconidae, 

 genus Bracon, and species simplex Cress. This insect appears on the 

 wing about the time or a little before the beetles emerge from the bark 

 in the early summer and commences to deposit its eggs by means of a 

 long, stinglike ovipositor which it inserts in and through the bark 

 infested by different stages of the larvae, on or by which it places its 

 eggs. The minute maggot hatching from this egg attaches itself to 

 the side of its victim and sucks out and feeds upon the liquids of its 

 body. The beetle larva soon dies, and after the parasite larva has 

 attained its full growth as such it incases itself in a thin, paperlike 

 cocoon (PI. VII) in which it goes through its transformation to the 

 adult. It then emerges and in a like manner continues its good work 

 in destroying the destroyer. While cocoons of this parasite were fre- 

 quently met with in the larval mines of the beetle in nearly every 

 locality where infested trees were examined, it was nowhere common 

 enough to be of any special service except near the sources of the 

 Kennebago and Dead rivers. Here it was quite common and had 

 killed a great many larva?. In one tree as many as six cocoons were 

 found in a piece of bark 2 inches square. It is only in the thinnest 

 bark, however, that this parasite can do much good in destroying the 

 larvae, and since the beetles usually select only the old trees with thick 

 bark, and do not infest the tops where the bark is thinner, it would 

 appear that this parasite can not, alone, do a great amount of good. 

 In connection with other beneficial factors, however, it contributes its 

 share to reducing the numbers of the destructive beetles, and thus is 

 an important factor. 



A PREDACEOUS BEETLE. 



Different stages of a beetle closely related to the one that was intro- 

 duced by the writer into the spruce and pine forests of West Virginia 

 from Germany in 1892-93, to prey upon the destructive pine bark 

 beetles, were frequently met with when examining infested trees, but 

 were not especially common, except in the same section where the par- 

 asite was common. 



This beetle belongs to the order Coleoptera, family Cleridae, genus 

 Thanasimus, and species rivMLus. It is antlike in appearance, espe- 

 cial lv when running about cm the bark. The adult is about one-fourth 



