Xi Chu

The aphid Myzus persicae is an important agricultural pest relying on olfactory cues to find food and escape from predators. The considerable difficulty of anatomical manipulation and other related technical challenges may underlie the absence of studies systematically mapping the central projections of antennal sensory neurons in its central nervous system. We used mass stain, immunohistochemistry, laser scanning confocal microscope and three-dimensional reconstruction techniques to trace the central projections of sensory neurons from the antennae. The ipsilateral antennal nerve targets mainly the antennal lobe, the antennal mechanosensory and motor center, and most neuromeres of the ventral nerve cord. There are also several axons that project to other regions, like the contralateral antennal lobe, the contralateral antennal nerve, the ipsilateral calyx and some region of the protocerebrum. The numerous neuropils innervated by axons from the antenna indicate the multiple roles that this sensory organ serves in insect behavior, and the results which provide information about the basic anatomical arrangement of the olfactory nervous system in aphid M. persicae may provide some basic knowledge for the further investigations of the aphid.

The mechanism of sex pheromone reception in the male cotton bollworm Helicoverpa armigera has been extensively studied because it has become an important model system for understanding insect olfaction. However, the pathways of pheromone processing from the antenna to the primary olfactory center in H. armigera have not yet been clarified. Here, the physiology and morphology of male H. armigera olfactory sensory neurons (OSNs) were studied using single sensillum recording along with anterograde filling and intracellular recording with retrograde filling. OSNs localized in type A sensilla responded to the major pheromone component cis‐11‐hexadecenal, and the axonal terminals projected to the cumulus (Cu) of the macroglomerular complex (MGC). The OSNs in type B sensilla responded to the behavioral antagonist cis‐9‐tetradecenal, and the axonal terminals projected to the dorsomedial anterior (DMA) unit of the MGC. In type C sensilla, there were 2 OSNs: one that responded to cis‐9‐tetradecenal and cis‐11‐hexadecenol with the axonal terminals projecting to the DMA, and another that responded to the secondary pheromone components cis‐9‐hexadecenal and cis‐9‐tetradecenal with the axonal terminals projecting to the dorsomedial posterior (DMP) unit of the MGC. Type A and type B sensilla also housed the secondary OSNs, which were silent neurons with axonal terminals projected to the glomerulus G49 and DMP. Overall, the neural pathways that carry information on attractiveness and aversiveness in response to female pheromone components in H. armigera exhibit distinct projections to the MGC units.

The present study was dedicated to investigating the anatomical organization of distinct neuropils within the two brain hemispheres of a gynandromorphic moth of the species Helicoverpa armigera. High quality confocal imaging of a synapsin immuno-stained preparation combined with three-dimensional reconstructions made it possible to identify several brain structures involved in processing odor input and to measure their volumes in the male and female hemispheres. Thus, in addition to reconstructing the antennal lobes, we also made digital models of the mushroom body calyces, the pedunculus, and the vertical and medial lobes. As previously reported, prominent sexual dimorphism was demonstrated in the antennal lobes via the identification of a male-specific macroglomerular complex (MGC) and a female-specific complex (Fc) in each of the two brain hemispheres of the gynandromorph. Additionally, sex-specific differences were found in volume differences for three other neuropil structures—the calyces, pedunculus, and vertical lobe. The putative purpose of larger volumes of three mushroom body neuropils in females as compared to males is discussed.

The pheromone system of heliothine moths is an optimal model for studying principles underlying higher-order olfactory processing. In Helicoverpa armigera, three male-specific glomeruli receive input about three female-produced signals, the primary pheromone component, serving as an attractant, and two minor constituents, serving a dual function, that is, attraction versus inhibition of attraction. From the antennal-lobe glomeruli, the information is conveyed to higher olfactory centers, including the lateral protocerebrum, via three main paths – of which the medial tract is the most prominent. In this study, we traced physiologically identified medial-tract projection neurons from each of the three male-specific glomeruli with the aim of mapping their terminal branches in the lateral protocerebrum. Our data suggest that the neurons’ widespread projections are organized according to behavioral significance, including a spatial separation of signals representing attraction versus inhibition – however, with a unique capacity of switching behavioral consequence based on the amount of the minor components.

Although rats are known to emit ultrasonic vocalizations (USVs), it remains unclear whether these calls serve an auditory communication purpose. For USVs to be part of communication, the vocal signals will need to be a transfer of information between two or more conspecifics, and with the possibility to induce changes in the behavior of the recipient. Therefore, the aim of our study was to investigate the role of USVs in rats’ social and non-social investigation strategies when introduced into a large novel environment with unfamiliar conspecifics. We quantified a wide range of social and non-social behaviors in the seminatural environment, which could be affected by subtle signals, including USVs. We found that during the first hour in the seminatural environment the ability to vocalize did not affect how quickly rats met each other, their overall social investigation behavior, their passive social behavior nor their aggressive behavior. Furthermore, the non-social exploratory behaviors and behaviors reflecting anxiety/stress-like states were also unaffected. These results demonstrated that a disability to vocalize did not result in significant disadvantages (or changes) compared to intact conspecifics regarding social and non-social behaviors. This suggests that other (multi)sensory cues are more relevant in social interactions than USVs. Highlights - Devocalization had no effect on social interactions with unfamiliar conspecifics - Ability to vocalize does not change the quality or quantity of social behaviors - Devocalization had no effect on non-social behaviors in a novel environment - USVs did not play a communicative role in social behaviors - USVs did not play a role in non-social behaviors

The pheromone system of heliothine moths is an optimal model for studying principles underlying higher-order olfactory processing. In Helicoverpa armigera , three male-specific glomeruli receive input about three female-produced signals, the primary pheromone component, serving as an attractant, and two minor constituents, serving a dual function, i.e. attraction versus inhibition of attraction. From the antennal-lobe glomeruli, the information is conveyed to higher olfactory centers, including the lateral protocerebrum, via three main paths – of which the medial tract is the most prominent. In this study, we traced physiologically identified medial-tract projection neurons from each of the three male-specific glomeruli with the aim of mapping their terminal branches in the lateral protocerebrum. Our data suggest that the neurons’ wide-spread projections are organized according to behavioral significance, including a spatial separation of signals representing attraction versus inhibition – however, with a unique capacity of switching behavioral consequence based on the amount of the minor components.

The relatively large primary olfactory center of the insect brain, the antennal lobe (AL), contains several heterogeneous neuronal types. These include projection neurons (PNs), providing olfactory information to higher‐order neuropils via parallel pathways, and local interneurons (LNs), which provide lateral processing within the AL. In addition, various types of centrifugal neurons (CNs) offer top‐down modulation onto the other AL neurons. By performing iontophoretic intracellular staining, we collected a large number of AL neurons in the moth, Helicoverpa armigera, to examine the distinct morphological features of PNs, LNs, and CNs. We characterize 190 AL neurons. These were allocated to 25 distinct neuronal types or sub‐types, which were reconstructed and placed into a reference brain. In addition to six PN types comprising 15 sub‐types, three LN and seven CN types were identified. High‐resolution confocal images allowed us to analyze AL innervations of the various reported neurons, which demonstrated that all PNs innervating ventroposterior glomeruli contact a protocerebral neuropil rarely targeted by other PNs, that is the posteriorlateral protocerebrum. We also discuss the functional roles of the distinct CNs, which included several previously uncharacterized types, likely involved in computations spanning from multisensory processing to olfactory feedback signalization into the AL.

Even though insects have comparably small brains, they achieve astoundingly complex behaviors. One example is flying moths tracking minute amounts of pheromones using olfactory circuits. The tracking distance can be up to 1 km, which makes it essential that male moths respond efficiently and reliably to very few pheromone molecules. The male-specific macroglomerular complex (MGC) in the moth antennal lobe contains circuitry dedicated to pheromone processing. Output neurons from this region project along three parallel pathways, the medial, mediolateral, and lateral tracts. The MGC-neurons of the lateral tract are least described and their functional significance is mainly unknown. We used mass staining, calcium imaging, and intracellular recording/staining to characterize the morphological and physiological properties of these neurons in the noctuid moth, Helicoverpa armigera. All lateral-tract MGC neurons targeted the column, a small region within the superior intermediate neuropil. We identified this region as a unique converging site for MGC lateral-tract neurons responsive to pheromones, as well as a dense congregating site for plant odor information since a substantial number of lateral-tract neurons from ordinary glomeruli (OG) also terminates in this region. The lateral-tract MGC-neurons responded with a shorter peak latency than the well-described neurons in the medial tract. Different from the medial-tract MGC neurons encoding odor quality important for species-specific signal identification, those in the lateral tract convey a more robust and rapid signal—potentially important for fast control of hard-wired behavior.