894 PHOCEEDINGS OF THE THIRD ENTOMOLOGICAL MEETING 



No trouble is experienced from moulds. In any case mould grows 

 only on the cut surfaces of the log just as it does on felled logs in the 

 forest. 



For work on a larger scale outdoor cages are available (11' x 65' X 11' 

 and 6|'x6|'x 11') ; these are constructed of wire gauze ^'^" mesh and 

 angle-iron frame-work. Cages with brick walls and glass roofs are also 

 used. They are fitted with automatic emergence traps on the principle 

 of the window screen for house flies. 



The cages of the tyi^es described give only emergence records. 



The exact length of the life-cycle is obtained by direct inoculation 

 of logs with eggs of the borer under investigation. In order to determine 

 the lengths of the various stages, full-fed larvae of known ages are extracted 

 from infected logs and transferred to tubes with moistened wood dust. 

 The atmosphere of the pupal chamber is saturated and these conditions 

 are easily reproduced in the tubes and maintained by waxing the corks. 

 The tubes are kept in the dark at temperatures corresponding to insec- 

 tary or outdoor conditions and the changes of the insects observed. No 

 saprophytic moulds grow in these tubes, but parasitic fungi such as 

 Botrytis bassiana readily develop and permit one to eliminate the diseased 

 larvae at an early date. From experimental observation in tubes one can 

 determine the length of the pre-pupal period, date of pupation, date of 

 transformation, and length of the immature beetle period. When the 

 beetle is mature it emerges by eating its way through the cork. 



Interpretation of Emergence records. 



The correlation of the emergence records of wood-borers is obviously 

 best conducted by graphical methods but before one can construct curves 

 it is necessary to eliminate certain errors. 



Theoretically the daily emergences recorded in the breeding cage 

 notes are correct ; in practice errors arise from careless examination 

 or unavoidable neglect of the cages and other sources. Plotting the daily 

 emergence figures as recorded may therefore give misleading results. 

 Two methods of correction are employed, geometrical and mathematical. 



The first method may be used for smoothing off accidental irregula- 

 rities in the curves of a single series of observations. The accumulated 

 daily totals are plotted and a crave djawn with reference to the points ; 

 the curve values are substituted for the observed values and the theore- 

 tical daily values calculated by difference. 



In comparing the data for different series (of the same species) of the 

 same quality but of different weight, the observed values are reduced to a 

 common standard by the method of the weighted mean. A clearer 

 comparison is obtained by combLniug the daily values in groups of 5 or 7 ; 



