DINODERUS MINUTUS, S57 

make use of these old holes to enter the bamboo to egg-lay, 
boring away from the old gallery when they have got inside. 
When bamboos are in lengths it will be found that the beetles 
tunnel in them parallel to the long axis and form galleries which 
open at one of the ends. The bamboo is thus often completely 
hollow in parts without there being much outward evidence of 
its having been badly attacked. This is more especially the 
case when the beetles have entered and left by the same holes 
made at one of the ends of the bamboo (cf. the lengths of bamboo 
shown in Plate XXI). A feature which greatly adds to the 
insect’s power of doing serious damage is to be found in the fact 
that in the warmer parts of the country it passes through at least 
five, and perhaps more, generations or life-cycles in the year, 
It has been shown that the insect lays about 20 eggs, and there- 
fore one female beetle may produce the following progeny in 
the year, on the supposition that only five generations are passed 
through :— 
1 Female beetle. 
ist generation . I x 20 = 20 beetles, say, 3 males 
and $ females (the 
latter are, however, 
usually in excess of 
former). 
and - és I0 x 20 = 200 beetles, sny, + males 
and 3 females. 
3rd Hf . 100 x 20 = 2,000 Ditto. 
4th . ; 1,000 x 20 = 20,000 Ditto. 
5th % . 10,000 x 20 = 200,000 Ditto. 
If there is a 6th generation the number of females increases | 
to 2,000,000, 
Taking only 50 per cent. of the 5th generation beetles as 
maturing’ and laying eggs, we still have 1,000,000 insects as the 
progeny of the one mother beetle in the spring. This great 
prolificness easily explains why bamboos suffer so greatly from 
the shot-borer’s attacks throughout the country. 
The result of my observations in Calcutta showed me that 
at least five generations of the beetles issued between the last 
week in April and the end of October as follows :— 
The 1st taking about seven weeks, from end of April to 
the third week in June, to run through all its stages : 
