A study was undertaken to isolate entomopathogens of southwesterncorn borer, Diatraea grandiosella Dyer, and southern cornstalk borer, Diatraea crambidoides (Grote). Field-collecteddiapausing larvae of southwestern corn borer (three sites inMississippi) and southern corn stalk borer (one site in NorthCarolina), and a laboratory strain of D. grandiosella in thediapause state were maintained in a simulated winter followed by asimulated spring environment. Few larvae (≤6%) collected from any ofthe field sites died in the winter environment, and most insectmortality (11–25%) occurred after transfer of the larvae to thesimulated spring environment. Mortality during the simulated springperiod differed among the collection sites, and the highest mortalitywas recorded for southwestern corn borers from Washington County(25%), followed by Marshall (16%) and Oktibbeha (11%) Counties. Ahigh level of mortality was also observed in southern corn stalk borersduring the simulated spring period (27%). No viruses were observed,but a number of bacteria, microsporidia, and fungi were isolated fromboth southwestern corn borer and southern corn stalk borer larvae andpupae. In most instances, numerous bacterial taxa were isolated fromcadavers, but on some occasions a single taxon predominated. The mostprevalent bacterial taxon from larval and pupal cadavers wasEnterococcus faecalis (Andrewes & Horder) Schleifer &Kilpper-Balz, but Bacillus spp., Pseudomonasaeruginosa (Schroeter) Migula, and Serratia marcescensBizio were frequently isolated as well. Few fungi (1–7%) wererecovered from southwestern corn borer and southern corn stalk borerlarvae and pupae. The most common entomopathogenic taxon isolated wasBeauveria bassiana (Balsamo) Vuillemin from southern cornstalk borer larvae. Microsporidia were not isolated from southern cornstalk borers. However, Nosema spp. were isolated fromsouthwestern corn borer cadavers from Washington (15%), Marshall(1%), and Oktibbeha (3%) Counties in Mississippi. In addition, weobserved parasitism of southern corn stalk borer larvae byMacrocentrus cingulum Reinhard (Hymenoptera: Braconidae). Noparasitism of southwestern corn borers was observed. Isolates ofBacillus, Beauveria, Entercoccus,Nosema, Pseudomonas and Serratia wereall pathogenic to southwestern corn borer larvae under controlledenvironmental conditions, and with the exception of B.bassiana, these are novel pathogens of Diatraea cornborers.
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Vol. 93 • No. 6