RESUMEN
The morphology and ultrastructure of the olfactory sensilla on the antennae and maxillary palps were investigated through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their responses to five volatile compounds were measured using electroantenogram (EAG) and electropalpogram (EPG) techniques in the pumpkin fruit fly, Bactrocera depressa (Shiraki; Diptera: Tephritidae). Male and female B. depressa displayed distinct morphological types of olfactory sensilla in the antennae and maxillary palps, with predominant populations of trichoid, basiconic, and coeloconic sensilla. Basiconic sensilla, the most abundant type of olfactory sensilla in the antennae, could be further classified into two different types. In contrast, the maxillary palps exhibited predominant populations of a single type of curved basiconic sensilla. High-resolution SEM observation revealed the presence of multiple nanoscale wall-pores on the cuticular surface of trichoid and basiconic sensilla, indicating that their primary function is olfactory. In contrast, coeloconic sensilla displayed several longitudinal grooves around the sensillum peg. The TEM observation of individual antennal olfactory sensilla indicates that the basiconic sensilla are thin-walled, while the trichoid sensilla are thick-walled. The profile of EAG responses of male B. depressa was different from their EPG response profile, indicating that the olfactory function of maxillary palps is different from that of antennae in this species. The structural and functional variation in the olfactory sensilla between antennae and maxillary palps suggests that each plays an independent role in the perception of olfactory signals in B. depressa.
Asunto(s)
Antenas de Artrópodos/fisiología , Percepción Olfatoria/fisiología , Tephritidae/fisiología , Animales , Antenas de Artrópodos/ultraestructura , Femenino , Masculino , Tephritidae/ultraestructuraRESUMEN
Electrophysiological recordings from the labial and maxillary palps of the Asian longhorned beetle, Anoplophora glabripennis, revealed their ability to detect several volatile chemicals, including water vapor and acetic acid. The results indicate that these appendages may play a large role in this beetle's assessment of its immediate environment. A. glabripennis is a highly destructive, invasive pest that feeds preferentially on maple - but accepts many other tree species - in North America, warranting USDA quarantine zones and an eradication program. While control and sampling techniques are being developed for this insect, a better understanding of its sensory capabilities is helpful. Electropalpograms (EPGs) revealed that both the maxillary and labial palps are highly sensitive to changes in humidity, indicating the presence of hygroreceptors and the likely important role of humidity in such things as feeding and finding water or oviposition sites. Strong EPG responses to a narrow set of volatile chemicals indicate that olfactory sensory neurons (OSNs) on the palps may be tuned to a small number of volatile compounds. The types of odorant molecules eliciting responses indicate that there are likely both odorant receptors (ORs) as well as ionotropic receptors (IRs) expressed on the OSNs, enabling palp OSNs to be able to respond to acids and aldehydes such as acetic acid and butyraldehyde. There were no significant EPG responses to this species' trail-sex pheromone components, which may indicate that the trail pheromone is primarily perceived via gustatory receptors contacting the substrate. These results indicate that the palps have a role in the beetle's assessment of its immediate environment underfoot, and that the sampling of surface odors and humidity via mouth parts may be important to this species' success.
Asunto(s)
Escarabajos/fisiología , Sensilos/fisiología , Olfato , Animales , Escarabajos/ultraestructura , Femenino , Masculino , Sensilos/ultraestructuraRESUMEN
Here, we report that the olfactory attraction of the striped fruit fly, Bactrocera scutellata (Hendel; Diptera: Tephritidae), a serious pest of pumpkin and other cucurbitaceae plants, to cue lure and raspberry ketone is mediated by the maxillary palps. The antennae, bearing three morphological types (basiconic, trichoid, and coeloconic) of olfactory sensilla, in male and female B. scutellata exhibited significant electroantennogram (EAG) responses to a plant volatile compound, 3-octanone, and methyl eugenol, whereas cue lure, raspberry ketone, and zingerone that are known to attract several other species of Bactrocera fruit flies elicited no significant EAG responses from both sexes. In contrast, maxillary palps, housing one morphological type of basiconic sensilla, displayed the largest electropalpogram (EPG) responses to cue lure followed by raspberry ketone among the five compounds tested in male and female B. scutellata, with only minor EPG responses to 3-octanone, which indicates that the maxillary palps are responsible for detecting cue lure and raspberry ketone in this species. In field trapping experiments, significant number of male B. scutellata were captured in the traps baited with cue lure or raspberry ketone, in which the attractiveness of cue lure was significantly higher than that of raspberry ketone. Methyl eugenol and zingerone were not behaviorally attractive to B. scutellata although they elicited significant EPG responses. Our study indicates that the behavioral attraction of B. scutellata to cue lure and raspberry ketone is mediated by the olfactory sensory neurons present in the maxillary palps.