Oligophagous Helicoverpa assulta (Guenée) and polyphagous H. armigera (Hübner) are two sibling species, with tobacco as the shared host\|plant. The effects of plant volatiles from one variety of Nicotiana tabacum and four varieties of N. rustica on electrophysiological and behavioral responses of these two insect species were investigated in the laboratory. The results indicated that virgin and mated females of H. assulta elicited stronger EAG and behavioral responses to four tested N. rustica varieties than to N. tabacum, while H. armigera was reverse in responses. Females of the two Helicoverpa species responded more actively in EAG and behavioral experiments to the volatiles of tested tobacco varieties than males, so there were significant sexual differences of the two sibling species. The results of gas chromatography\|mass spectrum (GC\|MS) showed that, in comparison with K326, variety “makhorka” contained higher amount of nicotine, more sorts of green leaf volatiles and less amount of aromatic compounds, suggesting that the difference in sorts and relative concentrations of tobacco volatiles may lead to the different ovipositing preferences of two sibling Helicoverpa species to N. tabacum and N. rustica tobacco plants.