A tritrophic association is reported, involving a Colorado potato beetle (Leptinotarsa decemlineata) infected with Beauveria bassiana, which in turn was infected with Syspastospora parasitica.
As part of a program for sampling Beauveria bassiana infections in the Colorado potato beetle (Leptinotarsa decemlineata (Say); Coleoptera: Chrysomelidae) collected from a potato field at the Beltsville Agricultural Research Center in Beltsville, Maryland, USA, we observed that 1 out of ca. 300 infected beetles collected on July 25, 2003, at a site known as Sleepy Hollow (N 39° 01.978′, W 76° 55.857′; 39 m above sea level), exhibited mycoparasitic growth on B. bassiana (Figure 1a–c). The mycoparasite was identified as Syspastospora parasitica (Tulasne) Cannon & Hawksworth.
The genus Syspastospora (Ascomycota: Sordariales) was erected by Cannon and Hawksworth (1982) to accommodate Melanospora parasitica, one of several species distinguished from species of Melanospora by characters that include a long perithecial neck composed of parallel hyphae and distinctive ascospores. In addition to S. parasitica two other species have been described: S. boninensis (Horie et al. 1986) and S. tropicalis (García et al. 2002), both isolated from soil. S. parasitica is known only as a mycoparasitic hyperparasite infecting various entomopathogenic clavicipitaceous fungi, e.g., Beauveria, Hirsutella, Paecilomyces, and some verticillioid species (Cannon and Hawksworth 1982). S. parasitica produces black perithecia with a small globose base and exaggeratedly long necks out of which copious quantities of cylindrical ascospores with markedly truncate ends are released (Fig. 1).
S. parasitica has been reported on various entomopathogenic fungi infecting insects, e.g., B. bassiana attacking the ash weevil Stereonychus fraxini (Coleoptera: Curculionidae) (Markova 1991); Cephalosporium spp. (= Verticillium) attacking the Kenya mealybug Planococcus kenya Le Pelley (Hemiptera: Pseudococcidae) (Masaba 1988); Paecilomyces farinosus attacking an unknown insect (ARSEF 5375; USDA-ARS Collection of Entomopathogenic Fungal Cultures, Ithaca, NY); Paecilomyces tenuipes attacking Bombyx mori (Lee and Nam 2000); B. bassiana infecting Cydia pomonella (L.) (Lepidoptera: Tortricidae); Beauveria tenella infecting Melolontha spp. (Coleoptera: Scarabaeidae); Spicaria farinosa (=Paecilomyces farinosus) infecting Boarmia bistortata Goeze (Lepidoptera: Geometridae); and Spicaria fumosorosea (= P. fumosoroseus) infecting Thaumetopoea pityocampa (Schiff.) (Lepidoptera: Thaumetopoeidae) (Müller-Kögler 1961). Ours is the first report of S. parasitica (ARSEF 7285) on a Colorado potato beetle infected with B. bassiana.
In our experience S. parasitica may go unobserved on the host. On two occasions when B. bassiana was transferred to potato dextrose agar from the Colorado potato beetle corpse, the presence of S. parasitica infection was not observed, although S. parasitica perithecia developed on the B. bassiana mycelial mat in approximately 60 days. Similar examples from inoculation of the coffee berry borer, Hypothenemus hampei (Ferrari) (Coleoptera: Curculionidae: Scolytinae), simultaneously with B. bassiana and Syspastospora ascospores resulted in B. bassiana-induced coffee berry borer mortality in around five days; it was not until three months later that S. parasitica perithecia appeared and produced ascospores. The slow development of S. parasitica perithecia also occurred when cultures of Syspastospora were started with ascospores that were contaminated with B. bassiana. In this case, B. bassiana grew within days but S. parasitica perithecia did not appear until almost one month later. In contrast, perithecia plated directly over B. bassiana cultures developed new ones in about 4 days at 25°C.
We thank Ann Sidor for collecting the insects. Part of this study was supported by the National Science Foundation (DEB-0072741 to MB).