Infectious enterococcus from Heliothis virescens × H. subflexa backcross hybrids (Lepidoptera: Noctuidae)

Abstract

Plating assays have revealed the presence of a bacterium in extracts of tissues from backcross hybrid insects, derived from crosses between Heliothis virescens and H subflexa, a bacterium found rarely and in much lower abundance in either of the 2 parent species. The bacterium is primarily localized within the gut but is also consistently recovered in small numbers from other somatic and germinal tissues. Fatty acid profile analyses and the sequence of its 16s ribosomal RNA indicate that the bacterium is an Enterococcus related to Enterococcus sulfureus and E. casseliflavus, species that previously have been encountered in insects and on plant tissues. Injection of the Enterococcus into H. virescens hosts results in the establishment of a bacterial infection similar to that of naturally infected backcross hybrids in terms of tissue distribution and relative magnitude among tissues. Like backcross hybrid males, almost 90% of H. virescens male moths mfected as larvae were sterile in single pair test matings. The inability to either rescue male fertility in backcross lines cured of the Enterococcus or to observe characteristic abnormalities in sperm ultrastructure, however, casts doubt on the likelihood that this microorganism is the proximate cause of male sterility in backcross hybrid insects.