December, '14] WEBB: RICE WATER- WEEVIL 435 



retreat, as if to make itself doubly secure, the larva spins a thin silken 

 sac or cover about itself. The writer has found as many as fifteen 

 pupal cells attached to the roots of one rice plant. 



The pupa shows somewhat the form of the adult, but is entirely 

 white like the larva. The duration of the pupal stage is probably 

 from one to two weeks. When fully mature the adult breaks through 

 the wall of the pupal cell, crawls up the root to which the pupal cell 

 was attached, and so escapes to the open air. 



The length of time the insect spends in each of these four stages is 

 not definitely known. However, the time from deposition of the 

 egg to the young adult stage in the spring has been approximately 

 determined. In a plot of rice which w^as first flooded on June 1, 1912, 

 the writer found a young adult in a pupa case on July 8, 1912. The 

 egg could not have been deposited before the rice was flooded, and, 

 supposing it to have been deposited the first day of flooding (June 1) 

 the time occupied in reaching the adult stage by July 8, was thirty- 

 .eight days, or five and one-half weeks. It is, of course, possible that 

 even less time than this was actually occupied by the insect in pass- 

 ing through the different stages. 



Generations 



Various cage tests and field observations, conducted by the writer, 

 have shown that, under favorable conditions, at least a partial second 

 generation of rice water- weevils in a season is possible. 



On July 29, 1912, a pan of growing rice, known to be infested with 

 larvse hatched from eggs deposited bj^ over-wintered adults, was placed 

 in a cage. By the side of this pan within the cage a pan of uninfested 

 rice was placed, the object being to determine whether or not, when 

 young adults emerged from the infested rice, they would deposit eggs 

 in the uninfested rice, and so start another generation the same year. 

 On August 31, 1912, the roots of two or three rice plants in the last 

 mentioned pan were washed out, revealing one medium-sized larva. 

 On September 23, 1912, the roots of several more plants in this pan 

 were washed out and six larvse were found. The pan of old rice from 

 the other end of cage was then removed, and, no weevils being observed 

 in the cage, a small quantity of dead grass (previously shaken out) was 

 placed there to provide hibernating quarters for any adults that might 

 later emerge from the remaining pan of rice. On April 6, 1913, the 

 dead grass was taken out of cage and carefully shaken out over a table. 

 Eight living rice water-weevils and the remains of one dead one were 

 thus disclosed. 



Another cage test, practically a duplication of that just described, 



