Hymenoptera 
Acantholyda erythrocephala (L.) Europe, 
Japan Pine 
Caliroa cerasi (L.) Europe Cherry, 
shadbush 
Diprion similis (Hartig) Europe Pine 
Eriotremex formosanus (Matsumura) Asia, Taiwan Oak 
Fenusa dohrnii (Tischbein) Europe Alder 
F. pusilla (Lepeletier) Europe Birch 
F. ulmi Sundevall Europe Elm 
Gilpinia frutetorum (F.) Europe Pine 
G. hercyniae (Hartig) Europe Spruce 
Hemichroa crocea (Geoffroy) Europe Alder 
Heterarthrus nemoratus (Fallen) Europe Birch 
Neodiprion sertifer (Geoffroy) Europe Pine 
Pristiphora erichsonii (Hartig) Eurasia Larch 
P. geniculata (Hartig) Europe Mountain-ash 
Profenusa thomsoni (Konow) Eurasia Birch 
Sirex juvencus juvencus (L.) Europe Pine, fir, 
spruce 
Solenopsis invicta (Buren) South 
America General 
feeder 
Trichiocampus viminalis (Fallen) Europe Poplar 
Biological Control 
Biological control, in the classical sense, implies the introduction of alien 
parasites, predators, or disease organisms to suppress pest populations below an 
economically damaging level. The forest environment is the most stable plant 
community; therefore, it should be admirably suited to the practice of biological 
control. In fact, a number of introduced forest insects have been subjected to this 
type of control with great success, and some others with less success. The exposed 
feeders—defoliators and sucking insects—are most readily suppressed; insects that 
feed cryptically—such as bark beetles and borers—are least likely to succumb to 
biological control. 
Success in this field of endeavor is favored by proper packaging, rapid transpor- 
tation, good communication between shipper and receiver, and also among 
customs, quarantine, and postal officials. Contrarily, poor communication between 
parties, inefficient customs, quarantines, and postal services, may ruin biological 
control attempts. Political strife between nations may also interfere with the con- 
duct of biological control operations. 
Generally speaking, biological control efforts against forest insects have been 
limited to (1) the importation and establishment of foreign parasites and predators 
of introduced pests; (2) the transfer of parasites, predators, and disease pathogens 
from one region to another within the country; (3) the augmentation of established 
parasite and predator populations with field-collected or laboratory-reared indi- 
viduals; and (4) the use of microbial sprays to control outbreaks. 
The majority of importations of parasites and predators made before World War 
‘Il emphasized enemies of the gypsy moth, browntail moth, satin moth (/73, 1/74, 
6/3), European pine shoot moth, European pine sawfly, European spruce sawfly, 
balsam woolly adelgid, and larch casebearer. Since then, importations have been 
limited mostly to enemies of the gypsy moth, balsam woolly adelgid, larch 
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