8 PROCEEDINGS OF THE SECOND ENTOMOLOGICAL MEETING 
the idea that, because an insect is common, we know all about it and 
there is no need to keep exact notes of its occurrence. The facts are 
far otherwise. There is no insect, however common, of which we really 
know anything worth knowing, and it is by the accumulation of in- 
numerable records of information, each doubtless small and un- 
important but each exact and complete in itself, that we may hope to 
attain to a more complete knowledge. I may mention as examples 
the cases of Agrotis ypsilon and Pieris brassicae. 
As you all know, a good deal of work has been done with Agrotis 
ypsilon during the last few years, chiefly in connection with its occur- 
rence as a pest on the fal lands around Mokameh. These lands are flooded 
to a depth of several feet in the Rains and, as the river drops and these 
lands are left exposed, they are placed under cultivation with mixed 
winter crops which are attacked extensively by Agrotis ypsilon. I 
am not going to speak now of the control-measures which have been 
adopted in this case—we shall come to that later on during this Meeting— 
but of the occurrence of the Agrotis in this area and of the curious 
gap at present existing in regard to our knowledge of its lifehistory 
throughout the year. As I said just now, these lands are flooded through- 
out the Rains to a depth of several feet and can only be cultivated and 
crops sown after the water has dropped ; but, as soon as these crops 
begin to spring up, they are attacked by Agrotis larvee, and it is evident 
that the eggs are laid by the parent moths on the newly-exposed muddy 
lands. But where do these moths come from? They go on breeding 
on the Mokameh fal in increasing numbers from about the end of August 
or beginning of September—the date necessarily varies with the flooding 
of the Ganges—until December or January, when the numbers begin to 
drop, owing probably to the effects of the cold weather and parasitic 
attack, but the insect is found breeding until about the end of March. 
About the end of March or beginning of April we usually find a large 
number of moths and then these disappear and no trace of the insect 
can be found until about the end of August, when moths suddenly appear 
again to lay eggs on the newly exposed tal lands. What becomes of the 
insect during the period April-August under natural conditions? At 
Pusa we have been able to keep continuous broods going during this 
period, but the insects were obviously under unnatural conditions 
and did not seem at all happy, and it seems very unlikely that it passes 
through these months in an active state under natural conditions. 
Careful search in and around the affected tal lands has completely failed 
to discover Agrotis in any stage at this time of year, and at present we 
can only suppose—it is, mark you, merely a supposition and not an 
ascertained fact—that the parent moths of the earliest broods are migrants 
