Effects of Corn Stunt Spiroplasma on Survival of <I>Dalbulus maidis</I> (Hemiptera: Cicadellidae) Parasitized or Preyed upon by <I>Gonatopus bartletti</I> (Hymenoptera: Dryinidae) or Infected by <I>Metarhizium anisopliae</I>

Abstract

The effects of corn stunt spiroplasma (CSS), Spiroplasma kunkelii, on survival of corn leafhopper Dalbulus maidis (Delong & Wolcott) (Hemiptera: Cicadellidae), exposed to parasitism, fungal disease, or predation were investigated in the laboratory. Adult corn leafhoppers with or without CSS were exposed separately to parasitism or predation by Gonatopus bartletti, a parasitoid that acts also as a predator, or to infection by Metarhizium anisopliae, a pathogenic fungus, to evaluate the effects of CSS on corn leafhopper survival confronted with these natural enemies. CSS alone did not affect corn leafhopper survival, but differentially mediated survival of leafhoppers exposed to parasitism or predation by G. bartletti, or infection with M. anisopliae. CSS did not affect the survival of corn leafhoppers parasitized by G. bartletti: Survivorship of leafhoppers carrying CSS and parasitized by G. bartletti was ≈9%, whereas in the absence of CSS and parasitized it was ≈17%, but the difference was not significant. Similarly, CSS did not affect the survival of corn leafhoppers infected with M. anisopliae: Survivorship of leafhoppers carrying CSS and infected with M. anisopliae was ≈64%, whereas in the absence of CSS and infected with M. anisopliae it was ≈73%, but the difference was not significant. In contrast, CSS reduced the survival rate of corn leafhoppers exposed to predation by G. bartletti, though the effect was mediated by the incubation period of CSS. Corn leafhoppers exposed to predation and carrying CSS for 10 or 20 d had significantly lower survivorship rates, ≈54 and ≈47%, respectively, compared with those of leafhoppers carrying CSS for 2 d or free of CSS, ≈91 and ≈78%, respectively. The lower survival rate of corn leafhoppers carrying CSS and exposed to predation by G. bartletti, particularly of leafhoppers with longer CSS incubation periods, together with the lower survival rate of CSS in leafhoppers parasitized by G. bartletti documented in earlier studies, are suggested as factors limiting the abundance of the vector and plant pathogen in their shared area of origin.