40 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE, 1952 
containing 10 and L2 percent. Of the fumigants tried, IK'N. and 
ethylene dibromide mixtures were the Least injurious. In instances 
in which germination was affected the blackeye cowpeas appeared to 
be the most susceptible and the small whites the mosl resistant. 
FOREST INSECTS 
Characters Symptomatic of Tree Susceptibility to Pine Beetle 
Attack Determined 
It has been known for years that certain ponderosa pine-, showing 
symptoms of weakness and decline, were more susceptible to attack 
by t lie western pine beet le t han more vigorous fasl -growing t rees. In 
an effort to determine tree character- thai are indicative of high risk 
to attack, studies have been under way for some time to so classify 
these characters that they may be used in removing susceptible trees 
from stands through sanitation-salvage logging. Results have now 
been obtained from nearly 8,000 trees thai were classified and tagged 
10 years ago. These trees occurred in 30 separate 10-acre plot- in 
eastern Oregon. It was found that five character-, as follows, were 
the most, symptomatic of tree susceptibility to pine beetles: {a) Fad- 
ing or off color needles; (b) active spike tops; (c) very thin, open 
crowns; (d) dying terminal twigs and branches; and (e) short needles 
with small needle complements. 
Benzene Hexachloride Controls Turpentine Beetle on Pines 
Since 1949 the black turpentine beetle has been killing pines all the 
way across the South from the Atlantic into Texas. Prior to 1949 
this insect was considered of secondary importance since it was not 
known to be an outright killer. It is having a serious effecl on the 
naval stores industry; also, a number of owners of small plots have 
clear cu1 their timber rather than contend with the beetle. Research 
this year has been directed toward determining provisional methods 
of control. Benzene hexachloride dusts, water suspensions, and oil 
solutions have been found effective in tests and on an operational scale 
in cont rolling the beetle. The suspensions and oil solutions also were 
found effective in preventing and controlling active infestations in 
standing trees. 
Selective Tree Removal Reduces Damage by Western Pine Beetle 
The effort to develop an effective method of controlling the western 
pine beetle by removing and utilizing tree- that are most likely t«> be 
attacked by thi- insect has been very successful in certain of the in- 
terior type ponderosa pine stands of the We-tern States. Losses have 
been materially reduced where these pracl ices have been employed and 
more and more of the timber-owning and managing agencies in the 
region are modi fying their cutting operations to include the principles 
of high risk cuttings f'<>r the purpose of we-tern pine beetle control. 
Bark Beetles Controlled at Lower Costs 
In studies designed to improve met 1 km I- for controlling bark beel les 
with insecticides, tests were conducted in northern [daho to compare 
the effectiveness of ethylene dibromide-oil solutions ami emulsions. 
