Part VII] Beeson : Life History of Toon Borer. 
65 
Limits of the generation within 17 to 19 weeks. 
The fourth generation .—The theoretical date for fourth brood moths 
is in the fourth week of September ; recorded date is the 
Average development :— 
2nd October. 
Days 
Incubation period of egg ....... 
4— 5 
Period of first larval stage ....... 
5— 1 
„ second larval stage ...... 
8—21 
,, third larval stage ...... 
13—15 
,, fourth larval stage ..... 
20—23 
,, pupal stage ....... 
13—14 
Total cycle, egg to moth 
64—79 
Limits of the generation 17 to 19 weeks. 
The fifth or overwintering generation .—The theoretical date for fifth 
brood moths is in the third week of February ; the recorded date is the 
18th February. Average development:— 
Days. 
Incubation period of egg ...... 
. 4— 5 
Period of first larval stage ...... 
. 7— 9 
„ second larval stage ..... 
. 8— 9 
„ third larval stage ..... 
. 14—15 
„ fourth larval stage ..... 
. 101—117 
,, pupal stage ...... 
. 13—15 
Total cycle, egg to moth 
. 147—170 
Limits of the generation 28 to 31 weeks. 
The disparities between the theoretical and actual dates for the 
commencement of the successive generations are very small, and pro¬ 
bably to be accounted for by the fact that inside the insectary the 
maximum daily temperatures are lower, and the total effective 
temperature is obtained by the insect at a slower rate. 
In the accompanying Plate X, the annual succession of broods is 
shown in diagrammatic form. The points on the circumference of the 
outer circle indicate the earliest dates on which the stages normally occur 
in the year ; the connected points on the circumference of the inner 
circle indicate the latest dates on which the corresponding stages may 
occur. A reading taken along any one radius will reveal what stages 
of the borer are likely to occur on any one date. 
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