RATE OF INCREASE OF GIPSY MOTH. 111 
in successive years, the unhatched or latest clusters being easily distinguished from 
the hatched or ‘‘old” clusters, and the age of these latter, whether one, two, three, 
or more years, being indicated by their state of preservation. The ratio of the aver- 
age annual increase of 10 such colonies was found to be 6.42; that is, six or seven 
egg clusters on an average may be found in the second season to one of the first 
season. 
If the number of eggs deposited by the average female moth be 
set at 500, and if the sexes of her progeny are equally divided, a 
potential increase of 250-fold for each annual generation is provided 
for. Under complete control only one pair of moths would average 
to be produced from each mass of eggs deposited, and since each egg 
represents an individual embryo, all but 2 of each 500 must fail to 
reach full maturity. Reduced to percentage this is equivalent to 
the survival of 0.4 per cent and the destruction of 99.6 per cent of 
the gipsy moths in one stage or another every year. Since the total 
number of gipsy moths in any locality can not possibly be computed, 
the only method by which mortality through any cause may be 
expressed is on this basis. | 
It will surprise many who have not given the matter considera- 
tion to learn what an extraordinary apparent mortality it requires to 
offset a potential increase of 250-fold. The gipsy-moth caterpillars 
molt five or six times after they hatch and before they change to pupe, 
making the number of caterpillar stages six or seven. If through 
natural controlling agencies 50 per cent of the young caterpillars 
were destroyed in the first stage before they had molted, and this 
was followed by similar destruction of another 50 per cent in the 
second stage, and so on through the third, fourth, fifth, sixth, and 
seventh stages, respectively, and in addition 25 per cent of the pupe 
and 25 per cent of the adults before depositing their eggs were simi- 
larly destroyed, it would still permit of a sight annual increase. 
The following table Gf the incongruity of fractions as applied to 
insects may be overlooked) indicates the number of survivors of each 
stage resulting from the hatching of a mass of 500 eggs: 
Number 
Stage. Number.| Loss. remain- | Potential increase. 
ing. 
Per cent. 
Se ee Eee eee 500 0] 5 ' 250 fold. 
RUPLI IPLAING 2 oe ee Oe ee iis te: ( eee me 500 50 | 250 125 fold. 
OS eae Ee ee gaan second. ........- 250 50 | 125 _ 62 fold. 
(Pe ere een Serge nl el Pind. ees. 125 50 62 31 fold. 
OUD Ee I ee eee ee Woerths Seo. 22 62 50 31 | 15.5 fold. 
(2 SE es ee ee eee i251) ee ae 31 50 15.5 7.75 fold. 
IS. Se ee ee SEBGte! ot 15.5 50 7.75 3.875 fold. 
ses ES Seventh....... 7.75 50 3.875 | 2.906 fold. 
LES aye ae 2 Oe ee ee ee a 3. 875 25 2.906 | 2.179 fold. 
Penne re re ei EN ceded cueucd 2.906 25 2.179 | 1.634 fold. 
To give another illustration: The life of the gipsy-moth caterpillar 
is approximately seven weeks. If beginning on the first day after 
