DUTCH ELM DISEASE 11 



CARRIER BEETLES 



Of the elm bark beetles known to be carriers of the Dutch elm disease 

 fungus in Europe, two are considered of prime importance: Scolytus scolytus 

 Fab., the larger European elm bark beetle; and Scolytus multistriatus Marsh, 

 the smaller European elm bark beetle. Scolytus scolytus is considered the 

 more important of the two. In America, however, only Scolytus multistriatus 

 is known to be established. It is now considered to be the most important 

 insect carrier concerned in the spread of the causal fungus in the United States. 



An elm bark beetle, Hylurgopinus rufipes Eich., native to this country, may, 

 because of its habits, prove to be an important carrier. A recent report refers 

 to Scolytus multistriatus and Hylurgopinus rufipes as the two important vectors 

 of this disease in America. 



The Smaller European Elm Bark Beetle 



(Scolytus multistriatus) 



This beetle was first found in the United States near Boston in 1909. A 

 survey made in 1933 revealed the presence of the beetle in three rather large 

 distinct areas around the cities of Boston, New York, and Philadelphia. It 

 was undoubtedly introduced into this country at these seaports. Later surveys 

 show that these infestations have enlarged. 



In areas where the Dutch elm disease has occurred, there seems to be a 

 definite relationship between the abundance of this carrier beetle and the 

 prevalence of the disease. Because of this apparent relationship, the large 

 infestation of Scolytus multistriatus in the Boston area causes some anxiety. 



In a survey conducted by this Station in 1935, this beetle was found at 

 two points in western Massachusetts. These new infestations appear to have 

 extended from the New York infestation, which has spread up the Hudson 

 River Valley beyond Albany and also to points in Connecticut not far from the 

 Massachusetts line. Because the Dutch elm disease has spread into the 

 New York area, the western part of Massachusetts should be kept under 

 strict surveillance. 



Description of Scolytus multistriatus. The beetle is about one-eighth of an 

 inch long. It is shiny in appearance. The fore part of its body (head and 

 thorax) is black, while the posterior part (elytra) is dark reddish brown in 

 color. The ventral side of the abdomen (venter) slopes abruptly upward 

 toward the rear and has a spine-like projection near the lower edge (Figure 5,A). 



How the Beetle Spreads the Disease. The young beetles emerge from tiny 

 shot-hole-like openings in the bark of logs or dying and recently killed elm 

 trees. Some of these may be affected with the Dutch elm disease. Beetles 

 emerging from bark of diseased wood often carry spores of the causal fungus on 

 their bodies and in their digestive tracts. Flying to nearby healthy elms, 

 they may feed upon small twigs, at leaf axils, and sometimes on the buds 

 (Figure 6, upper right). Thus, emerging beetles which carry the spores of 

 the fungus may inoculate trees through bark or bud punctures made in feed- 

 ing. In this way, healthy elms may become infected. It is possible that 

 wind currents may carry beetles considerable distances beyond their normal 

 flights. In this way, it is not improbable that distant trees occasionally 

 may be attacked by spore laden beetles, and the disease thus introduced 



