as long a time before feeding as they would normally 

 on a corn leaf. They fed on the cut surfaces of the bean 

 pods first and then they worked their way inward. 



In order to maintain the high humidity favorable for 

 development of the young borers, as well as to keep the 

 beans fresh, each cage was placed on a dish partly 

 filled with water, as shown in figs. lA and 3. For use 

 with each No. 1 cage, a standard crystallizing dish, 60 

 mm. in diameter, was covered with muslin, batiste, or 

 organdy. The textile cover was kept taut by a celluloid 

 ring on the outside perimeter of the dish. The water and 

 the air space (3 mm.) beneath each cage helped to main- 

 tain the humidity in the cage at approximately 95 per 

 cent. It was found that, in the course of routine rearing 

 of mass cultures, there was no special need of keeping 

 saturated salt solution in the dish below the cage. If 

 the temperature was not subject to rapid changes, there 

 was no perceptible accumulation of condensed moisture 

 within the cage. 



As the young borers developed, and a part of the 

 food was consumed, a number of the borers appeared 

 outside the bean pieces and began crawling around in 

 the cages. At this time, two or three additional pieces 

 of beans were placed in each cage. The borers accepted 

 the fresh beans immediately, began to feed without hes- 

 itation, and ate their way into the beans. In about 2 ad- 

 ditional days, most of the borers were in the second 

 instar and appeared again crawling around in the cages 

 in search of food. By this time all the larvae easily ac- 

 cessible were transferred with a wet camel s-hair brush 

 to No. 2 cages. Each No. 1 cage was then placed on a 

 iray covered with corrugated paper, where the food in 

 the cage desiccated rapidly. In about 2 or 3 days all 

 the remaining borers crawled out of the beans and were 

 transferred without difficulty to No. 2 cages. 



About 30 second or third instar larvae were placed 

 in each No. 2 cage. iJeans, cut to suitable lengths, were 

 placed in a single layer on a screen disc, 2-3/4 inches 

 in diameter, made of standard 18 x 14 mesh copper win- 

 dow-screen wire, and a similar disc was placed on the 

 beans, fig. 16. The second screen wire disc provided a 

 place and spacer for the next layer of food and, at the 

 time of transfer of larvae from the No. 1 cage to the 

 No. 2 cage, was used to aid in stripping the larvae from 

 the wet brush without injuring them. 



The bottom screen disc in each No. 2 cage and the 

 aluminum pan in each No. 1 cage helped to protect the 

 permanent screen bottoms of the cages from the decaying 

 beans at the end of a phase of rearing and, being re- 

 movable, they also facilitated the cleaning of the cage. 



It was usually necessary to keep each No. 2 cage 

 for a few days above water to maintain high humidity in 

 the cage. A crystallizing dish of 90 mm. diameter was 

 the most suitable for this purpose. It was provided with 



a textile top, as described for the No. 1 cage. If it be- 

 came evident a few days later that the humidity in the 

 cage was too high, the cage was moved to a corrugated 

 paper surface for slow desiccation of food, usually for 

 as long as the cage was in use. 



The time the corn borers had to be kept in tiie No. 

 2 cage was normally 4 to 6 days, by which time they 

 had reached the late fourth or early fifth instar. 



Fourth and fifth instar larvae seen crawling freely 

 around in the cage were transferred with tweezers to the 

 No. 3 cage. It was advisable to place a loose-fitting 

 screen disc on the bottom of this cage before green 

 string beans, broken in half, were thrown loosely into 

 the cage. As the borers consumed a large quantity of 

 food in the fifth instar, there was no special need to 

 protect the food from dehydration. Therefore, the No. 3 

 cages were kept always on corrugated paper bases. To 

 provide a suitable place for pupation, a corrugated paper 

 strip (17 inches long, 1 inch wide) was placed around 

 the inside wall of the cage about half way between the 

 top and bottom of the cage, fig. 2C. If it did not stay in 

 place, it was fastened with a short strip of adhesive 

 tape. 



The number of borers reared in each No. 3 cage 

 was 15 to 20. Food was provided as long as needed. 

 After the borers had pupated, the corrugated paper strip 

 could either be removed and the pupae placed in ovipo- 

 sition cages, or the strip could be left in the No. 3 

 cage. In the latter case, the emerging moths clung to 

 the undersurface of the cage top, from which they could 

 be easily transferred to an oviposition cage. 



Although successive transfers of the corn borer 

 larvae from cage to cage required considerable labor, it 

 seemed advisable to adopt this method rather than try 

 to rear larvae to maturity in the same container. Compli- 

 cations resulting from excess humidity and from the in- 

 evitable putrefaction of the food after a certain period 

 could thus be avoided, and the chances for cannibalism 

 among larvae could be reduced. 



EVALUATION OF CONTINUOUS 

 MASS REARING 



Observations indicated that European corn borers 

 could be reared by the above-described method through 

 a number of generations without any noticeable degen- 

 eration or harm to them. In laboratory experiments under 

 controlled conditions, the larvae developed to the same 

 size as did fifth instar larvae in the first generation of 

 the bivalent race of the European corn borer in the field. 

 They did not show a tendency to go into diapause. The 

 moths may have been somewhat smaller in size than 

 those that emerged from hibernating larvae collected in 

 the field. The time necessary (or development of the 



