KNTOMOLOGV AND I'LANT QUARANTINE 
21 
have either not prevented infestation or have been destructive tO' the »e<^iugs 
as well. Poisoning the foliage of nearby host plants in order to kill the adult 
insects does not appreciably decrease the leaf chafer population. However, 
many tests indicate strongly that heavy populations of grubs may be ade- 
Quately controlled by proper applications of carbon disulphide to the infested 
soil. 
In the case of plantations, observations over several years have proved that 
a heavy population of white grubs in the sod prevents the successful establish- 
ment of a plantation. This can best be determined by actual sampling of the 
proposed plantation site. losses in plantations can be reduced by avoiding 
areas that are heavily infested or by using wide deep furrows in which tO' 
Ijlant in such areas. Indications are strong that grub abundance in a given 
area is controlled by the presence of suitable host trees and shrubs for the 
adult beetles. It is believed, therefore, that white grub populations in nurseries 
can be reduced by avoiding the use of these more favored host plants as hedges 
or ornamental plantings around such nurseries and by destroying as much as 
possible of such material as occurs naturally in or near the nurseries. 
INSECTS AND THE DUTCH ELM DISEASE 
Work upon insect carriers of the Dutch elm disease was continued both at 
Morristown, N. J., and at Oxford, England. The work at Morristown had 
l)reviously established beyond doubt that the smaller European elm bark, 
beetle is a frequent vector, but it is also now known that the native elm bark 
beetle can and does perform the same function. In the former case the young 
beetles' habit of feeding in the crotches of twigs makes it an effective vector. 
In the case of the native elm bark beetle the young adults emerging in the 
fall often bore into the bark of living elm trees and there pass the winter. 
Their burrows are often extended entirely through the bark to the xylem, and 
if such beetles are contaminated with the fungus, the disease often develops 
nm\ kills the tree. In infected areas such as those in Cleveland, Ohio, and 
Indianapolis, Ind.. where no European elm bark beetles are known to occur, 
the native beetle is almost certainly the vector. 
During the year more than 10,000 insects were collected from felled elm 
trees put down at various points in the badly infected area of New Jersey. 
These insects were carefully collected in individual capsules and later cul- 
tured for the presence of the Dutch elm disease fungus. Many species of in- 
sects were collected, but of these only six were contaminated with the disease. 
These are Scolytus viuUi.striatus Marsh., Hiflurgopinu.s rufipcs Eichh., Mag- 
(lalis armicoUis Say, Xylosandrus f/crmanns Bldfd., Xulohiops oas'ilare Say, 
.and Conotrachelns analf/Iypticus Say. Of these only the first two showed con- 
tamination in any significant percentage of the numbers cultured. 
PINE SCALE INSECTS 
Both in the West and in several points in the East a blighted condition of 
the twigs of several species of pines has been found associated with infesta- 
tions of different species of Matsucoccus. In the Prescott National Forest and 
at other localities in the Southwest the association of these scjiles with the 
Prescott twig blight has been so close as to suggest that the scale insect may 
be an important factor. An intensive study, both on the Prescott form and on 
an eastern species affecting pitch pine, has been begun and will be continued 
• on Emergency Conservation Work funds. 
SPRAYING EXPERIMENTS 
Considerable progress was made in developing concentrated mixtures of many 
of the well known insecticides used in insect control. These concentrated mix- 
tures adhere better, and a greater deposit is obtained per unit area of leaf 
surface than with the conventional spray mixtures. Only from 1 to 10 gallons 
of the concentrated mixture is required per acre as compared with 4(K.> to 700 
gallons of the ordinjiry mixture. This is such a great saving in weight that it 
can be used in spraying from the air and the costs still kept lower than with 
ground spraying. In cooperation with other agencies, concentrated mixtures 
of certain insecticides were a]>plied from an autogiro in experiments to control 
heavy mixed infestations of the .spring cankerworm and fall cankerworm at 
Morristown, N. J., and for the gypsy moth at Freetown, Mass. In these tests 
