The antennal lobe of the moth brain is the primary olfactory center processing information concerning pheromones and plant odors. Plutella xylostella is a major worldwide pest of cruciferous vegetables and its behavior is highly dependent on their olfactory system. However, detailed knowledge of the anatomy and function of the P. xylostella olfactory system remains limited. In the present study, we present the 3-Dimentional (3-D) map of the antennal lobe of P. xylostella, based on confocal microscopic analysis of glomerular segmentation and Neurobiotin backfills of Olfactory Receptor Neurons (ORNs). We identified 74–76 ordinary glomeruli and a macroglomerular complex (MGC) situated at the entrance of the antennal nerve in males. The MGC contained three glomeruli. The volumes of glomeruli in males ranged from 305.83 ± 129.53 to 25440.00 ± 1377.67 μm3. In females, 74–77 glomeruli were found, with the largest glomerulus ELG being situated at the entrance of the antennal nerve. The volumes of glomeruli in females ranged from 802.17 ± 95.68 to 8142.17 ± 509.46 μm3. Sexual dimorphism was observed in anomalous supernumerary, anomalous missing, shape, size, and array of several of the identified glomeruli in both sexes. All glomeruli, except one in the antennal lobe (AL), received projections of antennal ORNs. The glomeruli PV1 in both sexes received input from the labial palp nerve and was assumed as the labial pit organ glomerulus (LPOG). These results provide a foundation for better understanding of coding mechanisms of odors in this important pest insect.
Using scanning electron microscopy, we investigated the distribution of the trichoid, basiconic, and coeloconic sensilla on the antennae of the diamondback moth (DBM; Plutella xylostella). The trichoid sensilla were the most abundant sensory organ, and male moths had significantly more than females. Conversely, basiconic and coeloconic sensilla were found more frequently on female than on male antennae. We performed experiments with various degrees of antennal ablation and demonstrated that DBM antennae play a key role in the control of mating and oviposition. We found that neither oviposition preference nor mating behaviors changed significantly when less than 1/4 of both antennae were removed. However, there was a significant behavioral change when the antennae were ablated by more than half: with a decrease in antenna length, the successful mating rate decreased and mating peak was delayed. An otherwise consistent host preference for oviposition was eliminated when both antennae were completely removed. Furthermore, we found that the number of trichoid sensilla was positively correlated with mating rate and oviposition preference. However, the numbers of basiconic and coeloconic sensilla were not correlated with mating rate and mating peak, but highly correlated with oviposition preference. Taken together, our results indicate that antennal sensory information plays a critical role in the mating and oviposition behaviors of this economically important pest similarly like in other moths.
Antennal sensilla play an essential role in insect life because they receive environmental cues. Dioryctria rubella is an important pine pest in China, but information on the morphology and distribution of its sensilla is limited. To elucidate the mechanism of insect-plant chemical communication, we examined the insect antennae and sensilla by scanning electron microscopy. The results showed that the antennae of D. rubella were filiform and consisted of a basal scape, a pedicel, and a flagellum with tapered flagellomeres. We identified seven types of sensilla, including trichodea, coeloconica, auricillica, basiconica, styloconica (two subtypes), Böhm’s bristles, and squamiformia, all of which were distributed on the antennae of both sexes. Nevertheless, some sensilla exhibited various degrees of sexual dimorphism; for instance, sensilla trichodea, squamiformia, and basiconica were more abundant in males than in females. Many pores were observed on the surface of the cuticular wall in sensilla trichodea and auricillica, and their biological function may be related to olfaction. This study presented a thorough inventory of sensilla on the antennae of D. rubella and laid a solid foundation for future functional studies.
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