56 THE PLUM CURCULIO. 
TaBLeE XX.—Larvel instars of the plum curculio—Continued. 
Duration of larva Jinstars. 
Individual No. 
Third Fourth 
instar in 
fruit. 
First Second 
E : Total days 
instar. instar. instar. 
to adult. 
Days. Days. Days. Days. 
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Measurements were made of the width of head-casts of the respective larval molts in the case of one 
larva, as follows: 0.306 mm., 0.425 mm., 0.595 mm., 1.02 mm. 
Head measurements of 19 larve at time of leaving the fruit showed a range in width of from 0.935 to 
1.071 mm., the average of all being 0.998 mm. 
DEATH OF LARVZ IN FRUIT. 
There is much evidence to show that many larve die within the 
fruit, though the cause, or causes, of this mortality is not easy of 
positive determination. In general, if the fruit falls at the time or 
shortly after the egg is deposited, this insures favorable conditions 
for growth of the larve. If, however, the fruit remains on the tree, 
the chances are much more against their successful development, 
and in the case of some fruits, as the apple and pear, almost entirely 
so. Prof. Crandall has made interesting observations on the mortal- 
ity among larve in apples. In a lot of 716 fallen apples, 169 curculio 
larvee were found, 103 of which, or about 61 per cent, were dead, from 
causes not established. Most of the larvee found dead were less than 
half grown, and many were not more than 2 or 3 days from the egg. 
Although it is not so stated, it is probably true that these larvae were 
killed while the fruit was yet on the trees. 
The mortality of larve in fruit for the most part results appa- 
rently from the crushing effect due to the rapid growth of surround- 
ing tissues; and in the case of stone fruits, as peach and plum, the 
abundant secretion of gum is perhaps an additional factor. The 
extent of mortality also varies with the different kinds of fruit. 
Thus in the case of apple many observations show that larvee are 
almost never able to survive if the fruit remains hanging on the trees 
for some time after the hatching of the eggs. The eggs for the most 
part hatch, and the young larve begin to feed inward, but before 
they penetrate far they succumb. Such larve show evidence of 
having been crushed, and often the burrow behind them is well grown 
over. Apples punctured while still small are most likely to fall; and 
