BIONOMICS OF THE CHINCH BUG. 9 
The data obtained in connection with the experiments on the 
number and length of instars of 16 individuals have been summarized 
in Table 3. In another series of approximately equal number, under 
observation for about the same period as were those of 1919 given 
in Table 3, four molts only were observed and the nymphs were then 
in their penultimate stage. The length of the period of the first 
instar, according to Table 3, varies from a minimum of 6 to a maxi- 
mum of 18 days, the second varies from 4 to 9 days, the third from 
3 to 31 days, the fourth from 6 to 26 days, and the fifth from 10 to 26 
days. Taking the averages obtained in the series, the period of the 
second instar is the shortest, the third somewhat longer than the 
second, the fourth slightly longer than the first, and the fifth much 
the longest of all. The greatest number of days required for any 
one of the individuals in the series to reach maturity was 94, and the 
smallest number 51. The general average for the total length of the 
immature period in the series is 66.43 days. 
It is not unlikely that the length of the instars and the length of 
the immature period were somewhat extended, because the nymphs 
were kept under somewhat unnatural conditions. In this study of 
number and length of instars in this species small shell vials (30 mm. 
in length) were found the most convenient and satisfactory. These 
were stoppered with absorbent cotton and the cotton was moistened 
as often as necessary when observations were made. Small bits of 
cornstalks were supplied as food for the nymphs. It was necessary 
to be very cautious to prevent an oversupply of water from gathering 
on the sides of the vials. When droplets gather the nymphs, in 
crawling along the sides, are overcome by the water and become 
lielpless, and if not assisted to a drier place and the vial dried out 
will die in a short time. 
ECDYSIS. 
A short time before the nymph casts its skin it becomes much 
swollen, especially in the abdominal region. The abdomen is then 
much wider than the thorax, particularly in the region of the fourth 
and fifth segments. Before this it is about the same width as the tho- 
rax or a little wider. The period during which the nymph has this 
swollen appearance will be called the molting period, and prepara- 
tions are then being made by the nymph to cast off its outer cuticular 
layer. This period corresponds precisely to that in lepidopterous 
larva? known as the molting period, during which the larvae become 
sluggish, feed little or none, and prepare to shed their outer coat. 
Specimens used for drawings of the various nymphal instars by 
C. V. Riley apparently were all in the molting stage, as the figures 
representing the instars show the nymphs much swollen. These 
drawings, therefore, 'are incorrect, even if the insect should have 
