Sept. 15, 1925 
Behavior of Ph/ytophaga destructor Say 
573 
PRACTICAL APPLICATION 
A discussion of the use that has already been made of this informa¬ 
tion on emergence cages in investigations that have been conducted 
subsequent to those of cage development may be appropriate. The 
dark cage D has been the one adopted in most cases, and many un¬ 
published data on various treatments of stubble as a fly control have 
been compiled. Although this may be said to be the primary pur¬ 
pose of these cage experiments, it was also desirable to have a cage for 
use at u emergence stations” in comparison with migration screens 
and egg counts, as has been described by Gossard and Eastwood (4), 
Gossard and Parks (< 5 ), and later at “observation stations” as 
described by Drake, Fenton, and Butcher ( 3 ). The dark cage has 
given very satisfactory results in both cases, and when properly 
manipulated under the immediate direction of a trained entomologist, 
serves as a good indicator of Hessian-fly emergence. 
It might be well to discuss briefly the results of experiments with 
emergence stations and the part played by emergence cages, the 
detailed report of which will be published later. Such stations have 
been in operation at La Fayette, Ind., and Centralia, Ill., during the 
fall emergence of the fly for the years 1919 to 1923 inclusive, that 
at the latter location being under the immediate observation of 
W. B. Cartwright, of the Bureau of Entomology, United States 
Department of Agriculture. 
After this rather extensive use of emergence cages, migration 
screens, egg counts, and flaxseed examinations, dependence is now 
placed almost entirely on egg counts and flaxseed examination to give 
the emergence records which are most closely associated with infesta¬ 
tion of wheat. The reasons for this are the advantages of simplicity, 
high degree of responsiveness, economy, and accuracy. Many midges 
closely resemble Hessian flies in cages and on migration screens, 
whereas there is very little chance of mistaking anything for a 
Hessian fly egg. The flaxseed examination to determine the status 
of pupation proved to be a very important contribution to the 
emergence-station activities. 
The results obtained by this series of emergence stations have 
certainly demonstrated their value in the scientific study of this phase 
of the life history of the fly. Confidence in the ability thus to pre¬ 
dict the safe time to sow wheat any one year has not been experi¬ 
enced to nearly the extent that has been the case elsewhere. Without 
flaxseed examination, a peak of emergence may be obtained, but 
there is nothing to indicate that there may not be another peak. 
Even with the status of pupation determined by flaxseed examina¬ 
tion, actual emergence must occur before it can be heralded as such. 
By the time complete pupation and emergence have been determined, 
the sowing date will have been delayed five to seven days longer than 
necessary, a very vital matter to the farmer with some sizable acreage 
to sow. If regular sowing time arrives and passes and still a large pro¬ 
portion of the fly remains in the larval stage in the flaxseeds, just 
what policy is to be adopted? There can be no assurance that such 
larvae will remain in that stage until the following spring. They 
may pupate the very next few days after the safe sowing date has 
been announced, ana thus emerge at exactly the right time to do 
the most d&mage to young wheat. Such cases have occurred too 
66850—25t-6 
