Influence of Some Fatty Acids on Oviposition by the Bruchid Beetle, Callosobruchus maculatus

The cowpea seed beetle, Callosobruchus maculatus, will lay its eggs on many potential hosts and inert surfaces. Oviposition on glass beads is stimulated by coating them with individual fatty acids. Nevertheless, female beetles reject mung seeds less frequently than beads treated with either an extract of mung seeds or, especially, an extract of mung seeds plus oleic acid. The addition of oleic acid to the extract resulted in a change in the sequence of oviposition behavior, notably an increase in a raised body position indicative of hosts of low acceptability. Fatty acids are present in the epicuticular waxes of legume seeds; wax extract of mung bean contains 32.4% fatty acid and 14 alkanes, whereas a wax extract of chickpea contains 5% fatty acid and 18 alkanes. Thus, chickpea may be a less acceptable host for oviposition than mung bean because of physical differences and/or because of chemical differences, including a reduced total level of fatty acid or the high proportion of oleic acid it is reported to contain. It is concluded that an appropriate mixture of fatty acids in the epicuticular waxes stimulates oviposition but that an elevated level of oleic acid in conjunction with others is deterrent.