112 PROC. EXT. SOC. WASH.. VOL. 20, XO. :,, MAY. 



A CONVENIENT METHOD OF HANDLING LARGE NUMBERS OF 

 INDIVIDUALS IN LIFE HISTORY STUDIES OF INSECtS. 



BY R. A. CUSHMAX. 



Life-histoiy stuclie? of inserts wh?re it is desired to base the 

 results on large numb3rs of individuals in order to arrive at the 

 normal average- are frequently onerous and require much move 

 time than is available for the average worker. Moreover, many 

 gregarious insects do not act normally when caged singly. 



The writer has found the method of handling and keeping notes 

 outlined below very satisfactory both in point of time required 

 and in the large numbe of individuals that can be studied with a 

 minimum of effort. This method has undoubtedly been employed 

 by others, but it is outlined here for the benefit of those to whom it 

 may not have occurred. It is not applicable to all sorts of insects; 

 in fact, it is very likely limited in application to externally feeding 

 insects. 



The method of handling consists, in brief, in starting with an 

 ovipositing female or a large number of eggs or larvae in one cage, 

 and, as changes to be recorded take place, in transferring those 

 individuals that have passed through the change to another cage, 

 leaving the unchanged ones in the original cage. The number of 

 cages to be handled gradually increases, but never reaches the 

 number that would be necessary in starting with a similar number 

 of individuals isolated. Moreover, cages are not installed only 

 to be discontinued upon the death or loss of a single individual, 

 but death> and losses, are automatically eliminated by failing to 

 appear in subsequent cages and notes and do not interfere with 

 the continuity of the records. 



Each original cage is given a number or letter, and each subse- 

 quent cage is represented by a decimal, the first lot of individuals 

 changing being given the decimal 1, the second lot 2, and so on. 

 Thus the stage or instar of the insects in any cage is indicated by 

 the number of decimals. 



The notes are kept on cross-lined cards divided into quarter-inch 

 squares, and are arranged so that one square in each direction 

 represents a change of stage or instar. 



Perhaps the citing of a definite example of the use of the system 

 will explain it better than a general discussion. The writer has 

 investigated the life-history of the current-worm (Pteronidea 

 ribesii Scopoli), using this system. The study of each generation 

 was begun with individual females each given a Roman numeral. 

 Each female was caged on a single currant leaf and the cage 

 moved each da}' to a new leaf as long as oviposition continued. 

 Thus were obtained data on the daily and total oviposition of the 



