CONTINUOUS MASS REARING 



of the European Corn Borer in the Laboratory 



Paul Surany* 



Several years ago, in the course of a research proj- 

 ect designed to explore the possibilities of biological 

 control of the Kuropean corn borer, Pyrausta nubilalis 

 (Ilbn.), there was an acute need for a large and steady 

 supply of corn borer larvae in all instars. 



The rearing of corn borer larvae in small numbers 

 has been reported by a few workers. In laboratory tests 

 involving several living plants, Mathes (1936) had re- 

 ported that green beans followed by green peas consti- 

 tuted the most successful laboratory diet for corn borer 

 larvae. In similar tests, Bottger (1940) had found that 

 green beans, lettuce, and green peas, as well as some 

 strains of corn, were satisfactory food plants, lie had 

 indicated that "food materials rich in glucose fulfilled 

 the borer's nutritive requirements far better than did 

 those high in either sucrose or starch." In nutrition 

 studies of corn borer larvae, Bottger (1942) and Beck, 

 Lilly, & Stauffer (1949) had successfully used synthetic 

 culture media as food. The methods developed and de- 

 scribed by these workers, although helpful, were inad- 

 equate to produce the large and continuous supply of 

 larvae needed for the research project on biological 

 control of the corn borer. 



FOOD FOR CONTINUOUS MASS REA??ING 



In the continuous mass rearing operations reported 

 here, various culture media tried as food for the corn 

 borer larvae proved to be unsatisfactory, find it was 

 concluded that, under the prevailing laboratory condi- 

 tions, only living or fresh plant material could meet 

 the food requirements. 



Corn, Zea mays L., the common host plant of the 

 larvae, was considered unsatisfactory because an ade- 

 quate supply of corn plants was not readily available 

 throughout the year and because small pieces of the 

 plant tended to wilt quickly, mold readily, and become 

 unpalatable to the larvae. 



After tests had been made of most of the fresh 

 plant materials available throughout the year in grocery 

 stores, the pods of string beans, Phaseolus vulgaris L., 

 (either green or wax beans) were selected as the most 

 satisfactory food for the corn borer reared under labora- 



"^At the time the reaearrh reported here was done. Dr. Surany was 

 Associate EntomoIoKJst of the Illinois Natur.'il History Survey at Urt)ana. 

 Now employeil a^ an entonnjloK'ist by the South Pacific Commission, he 

 i« workinK on diseases of the rhinoceros beetle, a pest of coconuts, in 

 several countries of the South Pacific region. 



tory conditions. The larvae, first and later instars, ac- 

 cepted the fresh string bean pods without hesitation, 

 and their attitude toward the pods did not differ much 

 from their attitude toward pieces of the corn plant. 



One of the chief advantages in using bean pods as 

 food for corn borer larvae is in the fact that the pods 

 usually do not decompose rapidly. On the surfaces cut 

 with a sharp knife, the bean pieces quickly develop a 

 callus tissue, which serves as a barrier against inva- 

 sion of microorganisms. No unusual measures against 

 contamination were necessary to prevent decomposition 

 of the beans by molds and bacteria during a single 

 phase of the rearing process. 



EQUIPMENT FOR CONTINUOUS MASS REARING 



In order to secure a large and continuous supply of 

 corn borer larvae for the experiments in biological con- 

 trol, it became necessary to design and construct spe- 

 cial equipment, principally containers in which the 

 larvae could be reared. 



One of the requirements for continuous mass rear- 

 ing of corn borer larvae was a simple means of main- 

 taining humidity in the rearing containers at or near the 

 level optimal for the development of the larvae. The 

 early instars require a humidity level near the saturation 

 point which, unfortunately, is optimal for the develop- 

 ment of molds and putrefying bacteria. The need of 

 costly and complicated machinery for critical humidity 

 control was overcome by scheduling each of three suc- 

 cessive phases in the rearing of the larvae in a differ- 

 ent type of container. In the interest of efficient work, 

 cages of three different sizes were designed with the 

 aim of providing each cage with its own physical atmos- 

 phere. 



The cages constructed for continuous mass rearing 

 of the larvae are illustrated in fig. 1. Cages No. 1 and 

 No. 2 were made from Lucite or Plexiglass tubing, brass 

 screen wire, and glass. Cage No. 3 was made from sim- 

 ilar materials, except that a paper carton was substi- 

 tuted for the I.ucite tubing. 



i-'or the smallest cage, .\o. 1, fig. 2.4. a 1-5/8 inch 

 length was cut with a band saw from tubing that was 2 

 inches in diameter and had a wall thickness of one- 

 eighth inch. The edges of each length were finished 

 square on a lathe to form the cylindrical wall of a cage 

 1-1 /2 inches tall. I'^or the bottom of the cage a disc was 



