Tobacco Hornworms and Budworms 



Applying dried spores of Bacillus thuringiensis in a cornmeal bait 

 was tried in 1960 and found effective for killing budworms as well as 

 hornworms that damage tobacco. In earlier experiments, sprays and 

 dusts containing the spores killed hornworms, but gave only partial control 

 of budworms. Since budworms and hornworms attack tobacco at the same 

 time in the South, there is hope of adjusting dosage rates to get a combined 

 kill and avoid foliage damage. 



Adding cornmeal to spore dust preparations apparently induces bud- 

 worm larvae to eat avidly enough to take in spores for a high infection 

 rate. The spores do not kill at once, but worms that eat the spore -corn- 

 meal bait soon stop feeding and die. In limited experiments, the effective- 

 ness of the bait has equaled or exceeded the excellent control that growers 

 obtain with chemical insecticide sprays containing endrin. 



These experiments have been conducted on flue-cured tobacco in 

 North Carolina, South Carolina, and Florida. In Florida, work has been 

 done on both shade -grown and sun-grown tobacco. The spore bait is 

 effective for several days, and in a typical experiment four treatments 

 have been spaced over 2-week intervals. Hand dusters have been used, 

 but the best results have been achieved when bait was applied to buds and 

 upper leaves of tobacco plants by hand. 



Caterpillar Pests of Leafy Vegetables 



Bacillus thuringiensis is known to infect and kill many kinds of cater- 

 pillars that damage leafy vegetable crops. Pests susceptible to the 

 bacillus spores include the cabbage looper, salt-marsh caterpillar, im- 

 ported cabbage worm, beet army worm, and diamond-back moth. In some 

 field tests, the bacillus spores have given an unexpectedly light kill, 

 indicating that conditions favorable to the spores are still not thoroughly 

 understood. 



Among recent findings is evidence that the spores kill these leaf- 

 eating caterpillars by two-way action of infection and starvation. In field 

 cages in Arizona, for example, the bacillus spores in a dust application 

 halted leaf damage of large and active salt-marsh caterpillars, so that 

 scarcely a trace of feeding damage occurred for 8 days. 



A virus that controls the cabbage looper at times by natural spread 

 in crop areas has been studied for a number of years and is considered 

 helpful. Quantities of this microbial material have been applied for crop 

 protection by scientists. Like other viruses, this one can be mass-produced 

 at present only by using living insects. Finding a way to culture it on a 

 medium would bring this virus nearer to commercial production. 



Since some caterpillars that damage leafy vegetable crops are sus- 

 ceptible to this virus and also to Bacillus thuringiensis , ARS scientists 

 have made preliminary tests of mixing the two pathogen materials. If 

 dosages can be adjusted, the possibility is seen that a mixed treatment 

 might give a higher killing rate of some pests and at the same time kill 

 more kinds of pests than either pathogen applied singly. Mixing pathogens 

 with chemical insecticides is also being tried out for the same advantages 

 in fighting leaf -eating caterpillars. 



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