Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2000
Publication Date: N/A
Citation: Interpretive Summary: Little is known about the diseases that infect the southwestern corn borer, a major lepidopterous pest of corn throughout the southern U.S., and its close relative the southern corn stalk borer primarily a pest in states along the eastern coast. Overwintering larvae of the southwestern corn borer from three corn fields in Mississippi and the southern corn stalk borer one field in North Carolina were collected in the fall of 1998. The larvae were held in cold storage to simulate a winter environment for approximately 3 months. They were then placed in a spring environment for development into the adult stage. Dead or dying larvae and pupae were studied for possible disease organisms. To ensure that the isolated diseas candidates were pathogenic to the southwestern corn borer, healthy larvae were infected with each candidate. These larvae were observed for disease symptoms and dissected to verify presence of the test organism. No viruses swere observed, but a number of bacteria, microsporidia, and fungi were isolated from both corn borers. Some of these pathogens may have potential for management of these lepidopterous pests.
Technical Abstract: A study was undertaken to isolate entomopathogens of southwestern corn bore (SWCB; Diatraea grandiosella) and southern cornstalk borer (SCSB; Diatraea crambidoides). Field-collected diapausing larvae of SWCB, SCSB, and a laboratory strain of D. grandiosella were maintained in a simulated winter followed by a simulated spring environment. Very few larvae (?6%) collecte efrom any of the sites died in the winter environment, and most mortality ( 22%) occurred after transfer of the larvae to the simulated spring environment. Mortality during the simulated spring period differed among the collection sites, and the highest mortality was recorded for SWCB from Washington County (22%), followed by Marshall County (13%), and Oktibbeha County (7%). A high level of mortality was also observed in SCSB during th simulated spring period (17%). No viruses were observed, but a number of bacteria, microsporidia, and few fungi were isolated from both SWCB and SCS Slarvae and pupae. The most prevalent bacterial taxon from larval and papa cadavers was Enteroccus faecalis, but Bacillus spp., Pseudomonas aeruginosa and Serratia marcescens were frequently isolated as well. Nosema spp. were isolated from SWCB from Washington (15%) Marshall (1%), and Oktibbeha (3%) Counties in Mississippi. Isolates of Bacillus, Beauveria, Entercoccus, Nosema, Pseudomonas, and Serratia were all pathogenic to SWCB larvae under controlled environment conditions, and with the exception of Beauveria bassiana, these are novel pathogens of Diatraea corn borers.