Thirty-three crude drug extracts were screened for their tyrosinase inhibitory activity. Among them, the acetone extract of the rhizomes of Rheum officinale Baillon showed the strongest inhibitory activity. Tyrosinase inhibitory activity-guided fractionation and chemical analysis led to the isolation of two potent compounds, 3,4',5-trihydroxystilbene-4'-O-beta-D-(2"-O-galloyl)glucopyr anoside (1) and 3,4',5-trihydroxystilbene-4'-O-beta-D-(6"-O-galloyl)glucopyr anoside (2). These compounds showed a competitive inhibition against tyrosinase and also inhibited the melanin biosynthesis.

The cowpea weevil, Callosobruchus maculatus, is a major pest of stored pulses. Females of this species produce a contact sex pheromone that elicits copulation behavior in males. Pheromone was extracted from filter-paper shelters taken from cages that housed females. Crude ether extract stimulated copulation in male C. maculatus. Initial fractionation showed behavioral activity in acidic and neutral fractions. Furthermore, bioassay-guided fractionation and gas chromatography-mass spectroscopy (GC-MS) analysis of active fractions revealed that the active components of the acidic fraction were 2,6-dimethyloctane-1,8-dioic acid and nonanedioic acid. These components along with the hydrocarbon fraction, a mixture of C(27)-C(35) straight chain and methyl branched hydrocarbons, had a synergistic effect on the behavior of males. Glass dummies treated with an authentic pheromone blend induced copulation behavior in males. The potential roles of the contact sex pheromone of C. maculatus are discussed.

The southern cowpea weevil, Callosobruchus chinensis (Coleoptera: Bruchidae), is a major pest of stored legumes in warm temperate and tropical climates. The female sex attractant pheromone was extracted from filter-paper shelters taken from containers that housed virgin females. The extracts were purified by various chromatographic techniques, and the biologically active components in the fractions were screened by gas chromatographic-electroantennographic detection analysis with male antennae. Two compounds that elicited electrophysiological responses were isolated, and gas chromatography-mass spectrometry, nuclear magnetic resonance, and micro-chemical analyses suggested that the active compounds were homofarnesals, (2Z,6E)- and (2E,6E)-7-ethyl-3,11-dimethyl-2,6,10-dodecatrienals. Males of C. chinensis were significantly attracted to filter paper discs loaded with the synthetic compounds at 0.01-0.1 ng compared to solvent control in a Y-tube olfactometer assay. These pheromone components represent unique chemical structures within the genus Callosobruchus.

Differentiation of mate recognition systems is one of the important steps for speciation in animals. For some insects, a contact sex pheromone present on the cuticular surface is indispensable in discriminating reproductive partners. In Callosobruchus species (Coleoptera: Chrysomelidae: Bruchinae), contact sex pheromones have been found in two species, Callosobruchus chinensis (L.) and Callosobruchus maculatus (Fabricius). It was suggested, however, that these two species lacked the ability to discriminate their conspecific and/or heterosexual partners. To elucidate this inconsistency, we verified the existence of contact sex pheromones from two other species, Callosobruchus rhodesianus (Pic) and Callosobruchus analis (Fabricius). As a result, unlike C. chinensis and C. maculatus, the males of C. rhodesianus and C. analis were able to discriminate their heterosexual partners. Comparing cross‐copulation behavior, i.e., copulation behavior between two species, against these four species indicated that the mate recognition specificities were quite different. Males of C. rhodesianus and C. analis had highly species‐specific mating behavior, whereas males of C. chinensis and C. maculatus were much less specific. These results indicate that variation in mate recognition can arise even among congeneric species living in a sympatric environment, and this variation might have arisen during species differentiation. Based on our results in combination with previous reports on interspecific competition, we suggest that the observed asymmetric cross‐copulation behavior might be, at least partially, an adaptation for surviving interspecific competition.

A novel insecticide flupyrimin (FLP) with a trifluoroacetyl pharmacophore acts as an antagonist at the insect nicotinic acetylcholine receptor (nAChR). This investigation examines a hypothesis that the FLP C­(O)­CF3 moiety is primarily recognized by the β subunit-face in the ligand-binding pocket (interface between α and β subunits) of the insect nAChR. Accordingly, we evaluate the atomic interaction between a fluorine atom of FLP and the partnering amino acid side chain on the β subunit employing a recombinant hybrid nAChR consisting of aphid Mpα2 and rat Rβ2 subunits (with a mutation at T77 on the Rβ2). The H-donating T77R, T77K, T77N, or T77Q nAChR enhances the FLP binding potency relative to that of the wild-type receptor, whereas the affinity of neonicotinoid imidaclprid (IMI) with a nitroguanidine pharmacophore remains unchanged. These results facilitate the establishment of the unique FLP molecular recognition at the Mpα2/Mpβ1 interface structural model, thereby underscoring a distinction in its binding mechanism from IMI.