Analysis of Sterility in Hybrids from Interspecific Crosses Between Heliothis virescens1 and H. subflexa1

Abstract

Interspecific hybrids were produced from reciprocal crosses between Heliothis virescens (F.) and H. subflexa (Gueneé). When female H. subflexa were paired with male H. virescens, the offspring were abundant, but 40% of the hybrid females entered diapause. The hybrid females did not mate readily with males of either species; these females laid few eggs, but their sons were sterile as were those of the fertile daughters. When H. virescens females were paired with H. subflexa males, hybridization was more difficult, partly because of the poor performance of the H. subflexa males. They neither mated nor transferred sperm readily. Hybrid females from H. virescens females crossed with H. subflexa males did not enter diapause, mated readily, and had a reduced fertility. However, backcrossing these hybrid females to H. virescens males partially or completely restored the fertility of the males by the 3rd generation. The male hybrids of each reciprocal cross were nearly sterile when they were backcrossed to females of either species. Females mated with these hybrid males contained few eupyrene sperm in their spermathecae but copious amounts of apyrene sperm; these females mated repeatedly with the same male but laid less than the normal complement of eggs. Primary spermatocytes from both species had 31 pairs of chromosomes, but those from hybrid males generally contained only 20-28 bivalents.