Research Reports: Size Difference Among 16S rRNA Genes From Endosymbiontic Bacteria Found in Testes of Heliothis Virescens, H. Subflexa, (Lepidoptera: Noctuidae) and Backcross Sterile Male Moths

Abstract

Experimentally induced interspecific matings between Heliothis virescens male and H. subflexa female moths result in sterile male and fertile female offspring. The fertile female progeny can be backcrossed with H. virescens males to produce more sterile male and fertile female offspring. Successive generations of backcross female progeny continue to produce sterile male and fertile female offspring when backcrossed to H. virescens males. Backcross sterile males readily mate with wild-type H. virescens females under field conditions. Backcross male sterility is of interest for its potential to suppress populations of the pest moth Heliothis virescens. Rickettsia-like organisms have been observed in the testes of backcross sterile males and the two parental species of Heliothis. Prokaryotic endosymbionts have been associated with hybrid sterility in other insects. Therefore, we investigated Heliothis endosymbionts via an analysis of their PCR-amplified rRNA genes (rDNA). Prokaryotic-specific primers were used to amplify 16S rDNA from aseptically removed testes. PCR reactions without testes extract were negative. Endosymbionts from H. virescens and H. subflexa were genetically different. The size of PCR-amplified 16S rDNA indicates that endosymbionts in backcross sterile males originate from H. subflexa. Sterile males have essentially a H. virescens nuclear genome as a result of backcrossing. We propose that backcross male sterility results from an incompatibility between the maternally inherited endosymbiont type found in the cytoplasm and the predominantly paternal genetic material found in the nucleus.