corn borer larvae at three different temperatures is 

 shown in the accompanying table. 



Time needed for development (first instar-adult) of Kuropean 



corn borers reared on green bean pods in mass rearings. 



Days 



Temperature 

 70 degrees F. 

 80 degrees F. 

 90 degrees F. 



26-38 

 17-25 

 15-17 



The number of eggs produced by corn borer moths 

 in the laboratory varied considerably. The females had 

 a tendency to lay egg masses of the same sizes as 

 those of females in the field. 



For egg laying, the moths were kept in pint-size 

 ice cream cartons. The top and bottom of each carton 

 were removed and the bottom was replaced with a wire 

 screen, which served as the top wlien the carton was 

 inverted and placed on moist sand in a petri dish. A 

 removable wax paper lining was placed in each carton, 

 and on this lining the females I'aid their eggs. 



The practice of keeping detailed records in the 

 course of rearing operations proved to be very useful. 

 The origin and the longevity of parent adults and the 

 daily egg production were noted in relation to the fate 

 and development of the progeny. The records or case 

 histories could be used in the selection of strains from 

 the most vigorous cultures. Also, they could be traced 

 through a number of generations in the event of induced 

 or accidental infections, or they could be consulted in 

 nutritional or other studies. 



SPECIAL REARING TECHNIQUES 



Under certain circumstances, there was a need to 

 rear a large number of European corn borer larvae for 

 only a brief period for experiments of limited duration. 

 Sometimes it was necessary to rear either newly hatched 

 or fourth or fifth instar larvae in greater quantities than 

 could be handled by the established methods. 



Large numbers of newly hatched larvae could be 

 reared with very satisfactory results in containers made 

 from small paper cups (preferably souffle cups of 2-inch 

 diameter) and petri dishes. Moisture did not condense 

 within these containers. Three or four pieces of bean 

 pod and an egg mass of normal size were placed in each 

 cup, and the bottom part of a 5S mm. petri dish was 

 placed on the top. The container was tiien inverted and 

 a small quantity of melted paraffin was dropped around 

 the inside rim of the bottom of the petri dish to provide 

 a complete seal around the edge of the cup. Containers 

 of this kind, with the glass tops up, were placed several 

 together in a constant humidity chamber set at 90 per 

 cent humidity, or as an alternative each was placed in 

 a half-pint size ice cream carton together with a wad of 



wet cotton. The development of the borers could be ob- 

 served through the glass tops. 



If the borers were to be reared through several in- 

 stars, a hole was cut in each paper cup soon after the 

 larvae reached the second or third instar: this hole al- 

 lowed larvae to leave the cup and feed on fresh beans 

 placed loosely in the ice cream carton. 



For screening tests, it was frequently necessary to 

 havealarge number of late first instar corn borer larvae. 

 In such cases, the pieces of beans in which larvae were 

 feeding were split carefully along the sutures and sub- 

 merged in distilled water. A number of larvae would 

 leave the food immediately and they could then be 

 strained out of the water. The rest of the larvae could 

 be forced to leave the beans by repeated application of 

 low vacuum. The same method was used when there was 

 a need for a large number of later instar larvae in a 

 short time. 



Frequently, a considerable number of fourth and 

 fifth instar corn borer larvae were collected following 

 the dissection of infested cornstalks in field experi- 



Fig. 4. —Arrangement for mass rearing of corn borer lar- 

 vae of fourth and fifth instars. Cylindrical wire baskets con- 

 taining food are placed, and replaced as the food is consumed 

 by the larvae, in a 1-gallon ice cream carton. On the bottom 

 of the carton is a layer of moist sand, and around the inside 

 wall is a strip of corrugated paper to serve as a place for 

 pupation. 



