BIOLOGICAL-ACTIVITY OF DATURA-WRIGHTII GLANDULAR TRICHOME EXUDATE AGAINST MANDUCA-SEXTA LARVAE

Natural populations of Datura wrightii in southern California consist of two distinctly different phenotypes. The leaves of one phenotype ar e densely covered with nonglandular trichomes and feel velvety. The ot her phenotype is covered with larger type IV glandular trichomes that excrete a sticky exudate. Neonate larvae of M. sexta reared on velvety leaves developed significantly faster than larvae on sticky leaves. L arvae on sticky leaves took 28% longer to reach the prepupal stage. Su rvival and pupal weight were not significantly different between the t wo groups. First instars of M. sexta had a significantly higher consum ption rate on velvety leaves than on sticky leaves. Removal of the exu date from stickly leaves significantly increased larval consumption ra tes compared to unwashed controls. Female moths did not show an ovipos ition preference; both in the lab and in the field the two trichome ph enotypes of D. wrightii received similar egg loads. Because there were no significant differences in other nutritional factors between the t wo plant phenotypes, we concluded that the exudate was responsible for the effect. We isolated a complex mixture of sugar esters (SE) as the biologically active compounds in the exudate of D. wrightii. The SE m ixture was composed of glucose esterified with several combinations of straight chain C-6-C-9 acids. By comparing GC-MS spectra of synthetic SE with the SE extracted from D. wrightii, we identified one of the S E as 3'-O-hexanoyl glucose.