| The scarab beetle Holotrichia oblita Fald possess predominance in the underground pests in northeast area of china. Considering various shortages of chemical control, this paper studied the electrical physiology and behavioral actions of the scarabs to greenery odors from the relation of insect and plants and from the point of view of reception of insect to semiochemicals by using electroantennography (EAG) and wind tunnel. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the ulstructure of olfactory sensilla. Main results are as follows:(1) The obvious EAG responses to greenery volatiles (E-2-hexenal and 5-Methyl-1-hexanol) were observed in both sexes of H , oblita adults. When the tested dosage was below 1 mg, the EAG reactions to E-2-hexenal and 5-Methyl-1-hexanol was intensified gradually with the increasing of dosage in both sexes of the beetles, and the EAG reactions to the two volatiles presented saturated state at the maximal dosage of 1 mg. The EAG value of 5-Methyl-l-hexanol was always higher than that to E-2-hexenal from 10 ng to 100 μg in both sexes.(2) No evident differences were observed in the EAG responses to tested odors between light and night in both sexes of H, oblita. Therefore, the EAG experiments were not affected by light in H, oblita.(3) The EAG activity to greenery odors in females was always higher than in males, which showed that female H. oblita adults have higher sensitivity to greenery volatiles than males.(4) By wind tunnel tests, it was found that E-2-hexenal had orientating action toward H. oblita adults, however 5-Methyl-1-hexanol had no obvious functions.(5) Sensilla were located densely on the antennal lamellae in H. oblita. These sensilla were situated on the sunken cavity formed by the antennal cuticle depressions. Sensilla basiconica (s.ba) and sensilla placoidea (s.pl) are the most mommon type of sensilla on the lamellae, besides there were a few sensilla ampucellaceous (s.am), sensilla papilla (s.pa), sensilla auricillica (s.au) and sensilla campaniformi (s.ca). So s.ba and s.pl were concluded to be olfactory sensilla. S.ba have six types according to the shape of their cones, s.pl had five types.(6) A clear sexual dimorphism occurred to both sexes of H. oblita at the size of antennae and sensilla amount. The length of each lamella and the total number of sensilla in female antennae were remarkably shorter than in males. The total number of s.pl had no obvious differences between the both sexes, but s.ba in males were far more than in females, the total number of s.ba was nearly nine times of s.pl. Therefore, s.ba were suggested to be sexpheromone receptor and s.pl were used for reception of plant odors.(7) TEM showed the internal structure of olfactory sensilla: Each s.ba consists of cone, auxiliary cell, olfactory neurons and dendritic branches which were connected to olfactory neurons. On the wall of s.ba there are many micropores, the dendritic branches beneath micropores were connected with one to four olfactory neurons. The number of auxiliary cells is one or three.
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