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 cel l types were present in various abundances in all tissues examined, an d thus may derive from a common tissue such as epithelial tissue. Extr emely (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 no t successful. Cells of higher ploidy were not found in any of the tiss ues examined. Incomplete duplication of higher ploidy cells was found in both fat body and Malpighian tubules. The cells of the Malpighian t ubules were found to be inflated in DNA content relative to other tiss ues, for reasons unknown. Nuclei were analyzed from larvae of both a p yrethroid-resistant and a susceptible strain of H. virescens. Differen ces in DNA contents between strains were sex specific and were not con sistent with the hypothesis that large-scale DNA amplification contrib utes to pyrethroid resistance in the RR strain.