seek the whorl of the young corn plant as a favorite feeding place. Spores 

 landing here at the right time find infant borers and favorable warmth and 

 moisture. Timing for a high kill is critical because, as leaves open, the 

 fungus spores are on the growing leaves and are carried away from the 

 whorl. In field tests, the spores have usually been applied when 75 percent 

 of the plants show leaf feeding. A second application 5 to 7 days after the 

 first treatment has at times increased the effectiveness. The spores, for 

 reasons that are obscure, are sometimes less effective against second- 

 brood borers. Some of the factors that may be responsible are tempera- 

 tures, the maturing corn, and other environmental conditions that are less 

 favorable to the development of this disease in the insect. In some field 

 tests, the spores have been disseminated with a cornmeal bait. 



Evidence that the fungus spores can kill the European corn borer in 

 its adult stage was obtained recently in experiments with male and female 

 moths. In 5 days, all moths exposed to infection by the spores were dead; 

 whereas untreated moths were all alive. This suggests that applications of 

 the spores, rightly timed, might reduce egg laying. 



The bacterium Bacillus thuringiensis has controlled the young borers 

 as well as the fungus, or better. The bacillus spores have been tried in 

 granules and in sprays. The granules worked better than a spray, ap- 

 parently because the granules released spores in greater concentration in 

 the whorl, where the borers accumulated. 



The protozoan Perezia pyraustae , which is being studied for corn 

 borer control, causes a chronic disease that kills some borers before 

 they become adult and mate, and also lessens the capacity of female moths 

 that survive to lay fertile eggs. This protozoan was first found attacking 

 borers in American cornfields in 1949. It has since been reported in so 

 many localities that it appears to be in nearly every corn borer horde. 

 If its spores can be spread artificially, this protozoan may do more to 

 reduce borer populations. Efforts to understand this protozoan are in 

 early stages, and Iowa is one center for the research. Experiments have 

 shown that the parasite protozoan can infect the borer at all stages, from 

 egg to adult. A spore -counting technique, recently developed, has provided 

 a helpful tool for managing dosages of the spores to get the maximum 

 effect on borer larvae. In an individual borer, a heavy infection averages 

 about 86 million spores; medium infection, 25 million; and light infection, 

 7 million. 



Pink Bollworm 



In research to protect cottonfields against the pink bollworm, microbes 

 of several types have shown promise. Investigation of microbial materials 

 is included in a USDA-State -industry program organized to search in- 

 tensively for more effective and economical means of controlling this 

 formidable pest. In preliminary trials at the USDA Pink Bollworm 

 Laboratory in Brownsville, Tex., six fungi, nematode DD-136, and Bacillus 

 thuringiensis all were found highly destructive to larvae of the pink boll- 

 worm. Progress toward practical use has advanced furthest with the 

 bacillus, which is being tested on the pink bollworm to learn the tempera- 

 tures and other environmental conditions that promote the most effective 

 kill, and to compare the merits of soil and plant applications. 



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