Abstract: 【Aim】 To clarify the ultrastructure of antennal sensilla of adults of the black soldier fly, Hermetia illucens, and to explore the olfactory responses of its female and male adults to odorants. 【Methods】 The ultrastructure of antennal sensilla of H. illucens adults was observed by transmission electron microscope. The electroantennogram (EAG) responses and behavioral responses of female and male adults to four odorants including isovaleric acid, lactic acid, ethyl acetate and nonanal were measured by electroantennography and Y-tube olfactometer, respectively. 【Results】 The cuticular wall of trichoid sensilla on the antennae of H. illucens adults exhibited a thick structure devoid of pores, within which nerve dendritic branches were immersed in sensilla lymph. Basiconic bulge with several branches was observed in the cavity of coeloconic sensilla. The cuticular wall of the basiconic bulge displayed a thin composition with pores, within which nerve dendritic branches were immersed in sensilla lymph. EAG test results indicated that all the four odorants tested at various concentrations caused obvious EAG responses of adult H. illucens. The reactions caused by these odorants varied with the change in concentration. Both female and male adults exhibited the strongest EAG response to isovaleric acid, and the relative values of their EAG responses increased as the concentration increased. However, the EAG response of female adults to lactic acid initially increased and then decreased with the concentration increasing, while that of males showed the opposite trend. To the two odorants ethyl acetate and nonanal, the EAG response of female adults initially decreased and then increased with the test concentration increasing, whereas that of male adults showed a different and irregular trend. The behavioral choice test results demonstrated that lactic acid at the concentrations of 0.001-0.1 μg/μL had significant attraction to female adults, and 0.1 μg/μL isovaleric acid had significant attraction to male adults. 【Conclusion】 The trichoid sensilla on the flagellum of antennae of adult H. illucens may function as hygro- and thermo-sensilla, while the coeloconic sensilla on the flagellum might be olfactory sensilla. The antennae of both female and male adults are sensitive to high concentrations of isovaleric acid. Low concentrations of lactic acid and isovaleric acid have attractive effects on H. illucens adults, and could potentially be used as the components of attractants.

Key words: Hermetia illucens, transmission electron microscope, olfactory sensilla, electroantennography, behavioral choice, olfactory response