Characterization of oviposition attractants of Helicoverpa armigera in two solanaceous plants, Solanum viarum and Lycopersicon esculentum

The role of host plant chemicals in oviposition of Helicoverpa armigera Hiibner (Lepidoptera: Noctuidae) was studied in two solanaceous plants, Solanum viarum Dunal. and Lycopersicon esculentum Mill. Plant volatiles as well as chemicals extracted from leaves were bioassayed for oviposition attraction in a two-choice olfactometer, where mated adults were given equal opportunity for oviposition either on plant extract side or solvent check side. Two fractions of microwave-assisted extracts from leaves of both plants elicited strong oviposition response. Normal alkanes, 13,17,21-trimethylheptatriacontane and octacosane were the only chemicals present in these fractions of S. viarum, whereas besides these chemicals, few other n-alkanes and related primary alcohols and aldehydes were present in tomato foliage. Oviposition attractants were also present in volatiles of both plants. Two fractions from S. viarum containing several small molecular weight alkanes elicited strong ovipositional response. One of the two fractions of tomato volatiles that elicited moderate oviposition response contained predominantly 3-nitrobenzyl alcohol and minor amounts of 3-nitrobenzaldehyde, whereas the other that showed strong oviposition deterrent activity contained 3-nitrobenzyl alcohol and small amounts of docosane and trimethyldecane, in addition to an unknown compound. Although several chemicals in both plants were active in oviposition of H. armigera, we were not able to ascertain whether all or only certain specific chemicals are involved in this process. However, constancy in most of the identified compounds, especially n-alkanes in the two different genera Solanum and Lycopersicon could have formed the basis for host selection by H. armigera.