A special metal clamp rack was therefore designed 

 to hold the vials. With this device, the handling of large 

 numbers of individually reared larvae could be carried 

 out with ease and efficiency. The rack could be made 

 in various lengths to suit individual requirements. It 

 was found that racks accommodating 10 or 12 vials were 

 the easiest to handle. The racks were fashioned of 28- 

 gauge galvanized sheet iron (stainless steel would have 

 been more suitable) bent to the shape shown in fig. 5. 

 When a vial was to be placed in or removed from the 

 rack, pressure was applied to the top of the clamp 

 spring that held it in place. 



This clamp rack had several advantages. It made 

 possible the storage of vials in any desired position. 

 All the vials could be checked at a glance. Pluggingthe 

 mouths of vials with cotton in the usual manner was 

 completely eliminated. The formation of condensed 

 moisture inside the vials was reduced or eliminated by 

 air circulation through the screens. 



TESTS WITH INSECTICIDES AND PATHOGENS 



With the development of satisfactory laboratory 

 methods for the mass rearing of European corn borer 

 larvae, it became possible to develop techniques for 



special experimental work. The following received at- 

 tention: (a) application of insecticides and pathogens 

 to food or substrate; (b) reactions of larvae during peri- 

 ods of exposure to insecticides or pathogens; and (c) 

 estimation of amounts of insecticides or pathogens 

 ingested. 



For most of the laboratory experiments with insec- 

 ticides and pathogens, the simplest and easiest method 

 of feeding the corn borer larvae involved use of only 

 the pericarps of the string beans. The pods were split 

 lengthwise along the sutures, the seeds were removed, 

 and the halves were cut to suitable lengths. The split 

 bean pieces could easily be dusted or sprayed with a 

 solution or suspension, as well as dipped. As a sticker 

 and spreader, 0.1-0.3 per cent methylcellulose (\letho- 

 cel) was found to give very satisfactory results. The 

 bean pericarps offered large surfaces both for deposit 

 of insecticide or pathogen and for feeding. 



The conditions prevailing in the field on a com 

 leaf could be reproduced to a rather fair degree by us- 

 ing the floating leaf technique. A piece about 3 inches 

 square was cut from the distal end of a leaf of field 

 corn and a hole was punched in the center near the mid- 

 rib, fig. 6. The distal end was preferred to the proximal 

 end because it tended to be flat, rather than ruffled. If 



P^ig. 6. — Arrangement, A, for testing insecticide deposits on com leaf with the floating leaf technique. A piece of com 

 leaf is floated on water in a crystallizing dish and kept in place with a triangiilar-based anchor, S, fashioned from a glass rod. 

 The perpendicular part of the anchor is inserted through a hole in the center of the com leaf. With the help of this anchor, the 

 leaf can be lifted from the water and replaced in it. 



8 



