GENOME SIZE AND ENDOPOLYPLOIDY IN PYRETHROID-RESISTANT AND SUSCEPTIBLE STRAINS OF HELIOTHIS-VIRESCENS (LEPIDOPTERA, NOCTUIDAE)

Heliothis virescens (F.) males have a haploid genome size of 403.6 (2.3 +/- SD) million nucleotide pairs (Mnp), which is very close to that reported for tissues of other Lepidoptera (456-485 Mnp). Octaploid cell types were present in various abundances in all tissues examined, and thus may derive from a common tissue such as epithelial tissue. Extremely (i.e., 10(4)- to 10(5)-fold) polyploid nurse or silk gland cells are known in other Lepidopters. However, attempts to analyze salivary glands of H. virescens, which might also be highly polyploid, were not successful. Cells of higher ploidy were not found in any of the tissues examined. Incomplete duplication of higher ploidy cells was found in both fat body and Malpighian tubules. The cells of the Malpighian tubules were found to be inflated in DNA content relative to other tissues, for reasons unknown. Nuclei were analyzed from larvae of both a pyrethroid-resistant and a susceptible strain of H. virescens. Differences in DNA contents between strains were sex specific and were not consistent with the hypothesis that large-scale DNA amplification contributes to pyrethroid resistance in the RR strain.