Behavioural responses to mammalian grazing expose insect herbivores to elevated risk of avian predation.

Large mammalian herbivores (LMH) are important functional components and drivers of biodiversity and ecosystem functioning in grasslands. Yet their role in regulating food-web dynamics and trophic cascades remains poorly understood. In the temperate grasslands of northern China, we explored whether and how grazing domestic cattle (Bos taurus) alter the predator-prey interactions between a dominant grasshopper (Euchorthippus unicolor) and its avian predator the barn swallow (Hirundo rustica). Using two large manipulative field experiments, we found that in the presence of cattle, grasshoppers increased their jumping frequency threefold, swallows increased foraging visits to these fields sixfold, and grasshopper density was reduced by about 50%. By manipulatively controlling the grasshoppers' ability to jump, we showed that jumping enables grasshoppers to avoid being incidentally consumed or trampled by cattle. However, jumping behaviour increased their consumption rates by swallows 37-fold compared with grasshoppers that were unable to jump. Our findings illustrate how LMH can indirectly alter predator-prey interactions by affecting behaviour of avian predators and herbivorous insects. These non-plant-mediated effects of LMH may influence trophic interactions in other grazing ecosystems and shape community structure and dynamics. We highlight that convoluted multispecies interactions may better explain how LMH control food-web dynamics in grasslands.

Grasshoppers do not flee from their alarmed predators but from non-alarmed ones.

Alarm calls produced by basal prey have a well-known informative value. In multi-predator communities, mesopredators, when faced with top predators, may emit alarm calls that could inform basal prey about their lowered predation risk. To test this unexplored possibility, we conducted one field and one mesocosm experiment in which we simulated alarm and non-alarm calls from little owls (Athene noctua) as mesopredators and measured their effects on grasshoppers as prey of little owls but not of top predators. In the field experiment, we found that grasshopper species were significantly more abundant in patches where we simulated either the presence of scared little owls (alarm treatment) or no owls (control treatment) compared to patches where the presence of non-scared little owls (non-alarm treatment) was simulated. In the mesocosm experiment, locusts (Locusta migratoria) moved significantly more to exposed areas when we simulated the presence of scared little owls (alarm treatment) or of a granivorous bird (control treatment), while they moved to sheltered areas when we simulated the presence of non-scared owls (non-alarm treatment). These results show that prey could cue on predators' calls to assess their predation risk and make decisions, revealing unprecedented potential ecological consequences of alarm calls in invertebrate communities.

Linking cognitive strategy, neural mechanism, and movement statistics in group foraging behaviors.

Foraging for food is a rich and ubiquitous animal behavior that involves complex cognitive decisions, and interactions between different individuals and species. There has been exciting recent progress in understanding multi-agent foraging behavior from cognitive, neuroscience, and statistical perspectives, but integrating these perspectives can be elusive. This paper seeks to unify these perspectives, allowing statistical analysis of observational animal movement data to shed light on the viability of cognitive models of foraging strategies. We start with cognitive agents with internal preferences expressed as value functions, and implement this in a biologically plausible neural network, and an equivalent statistical model, where statistical predictors of agents' movements correspond to the components of the value functions. We test this framework by simulating foraging agents and using Bayesian statistical modeling to correctly identify the factors that best predict the agents' behavior. As further validation, we use this framework to analyze an open-source locust foraging dataset. Finally, we collect new multi-agent real-world bird foraging data, and apply this method to analyze the preferences of different species. Together, this work provides an initial roadmap to integrate cognitive, neuroscience, and statistical approaches for reasoning about animal foraging in complex multi-agent environments.

The ant and the grasshopper: Contrasting responses and behaviors to water stress of riparian trees along a hydroclimatic gradient.

Riparian trees are particularly vulnerable to drought because they are highly dependent on water availability for their survival. However, the response of riparian tree species to water stress varies depending on regional hydroclimatic conditions, making them unevenly vulnerable to changing drought patterns. Understanding this spatial variability in stress responses requires a comprehensive assessment of water stress across broader spatial and temporal scales. Yet, the precise ecophysiological mechanisms underlying these responses remain poorly linked to remotely sensed indices. To address this gap, the implementation of remote sensing methods coupled with in situ validation is essential to obtain consistent results across diverse spatial and temporal contexts. We conducted a multi-tool analysis combining multispectral and thermal remote sensing indices with in situ ecophysiological measurements at different temporal scales to analyze the responses of white poplar (Populus alba) to seasonal changes in drought along a hydroclimatic gradient. Using this approach, we demonstrate that white poplars along the Rhône River (France) exhibit contrasting responses and behaviors during drought depending on the latitudinal context. White poplars in a Mediterranean climate show rapid stomatal closure to reduce water loss and maintain high minimum water potential levels, although this results in a decrease in remotely sensed greenness. Conversely, white poplars located upstream in a temperate climate show high transpiration and stable greenness but lower minimum water potential and water content. A site in the middle of the gradient has intermediate responses. These results demonstrate that white poplars along a climate gradient can have a range of responses to drought along the iso/anisohydricity continuum. These results are important for future climatic conditions because they show that the same species can have different mechanisms of drought resilience, even in the same river valley. This raises questions regarding how these riparian tree populations will respond to future climatic and hydrological conditions.

Distribution patterns and potential suitable habitat prediction of Ceracris kiangsu (Orthoptera: Arcypteridae) under climate change- a case study of China and Southeast Asia.

Ceracris kiangsu (Orthoptera: Arcypteridae), is greatly affected by climatic factors and exhibits strong adaptability, posing a serious threat to the ecological environment. Therefore, predicting its potential suitable habitat distribution provides a proactive theoretical basis for pest control. This study using the Biomod2 package of R simulated and predicted the current and future potential distribution, area changes, changes in the center points of suitable habitats, and niche shifts of C. kiangsu under two different greenhouse gas emission scenarios, SSP1-26 and SSP5-85. The results show that: (1) Currently, the high suitability areas for C. kiangsu are mainly distributed in Yunnan, Jiangxi, Hunan provinces in southern China and phongsaly province in northern Laos. In the future, the center of the suitable habitat distribution pattern of C. kiangsu will remain unchanged, primarily expanding outward from medium and high suitability areas. Additionally, significant suitable habitats for C. kiangsu were discovered in Southeast Asian countries without previous pest records. (2) Compared to the present, the overall suitable habitat area for C. kiangsu is expected to expand, particularly under the SSP5-85 climate change scenario. (3) In the SSP1-26 and SSP5-85 climate scenarios, the geometric center of the suitable habitat generally shows a trend of gradually shifting northeast. (4) Under different climate scenarios, the suitable habitat of C. kiangsu has highly overlapping, indicating that the suitable habitat of C. kiangsu in the invaded areas is broader than in its native regions. In conclusion, the research findings represent a breakthrough in identifying the potential distribution areas of C. kiangsu, which is of great practical significance for the monitoring and control of C. kiangsu pest infestation in China and Southeast Asian countries.

Chromosome-level genome assembly of the morabine grasshopper Vandiemenella viatica19.

Morabine grasshoppers in the Vandiemenella viatica species group, which show karyotype diversity, have been studied for their ecological distribution and speciation in relation to their genetic and chromosomal diversity. They are good models for studying sex chromosome evolution as "old" and newly emerged sex chromosomes co-exist within the group. Here we present a reference genome for the viatica19 chromosomal race, that possesses the ancestral karyotype within the group. Using PacBio HiFi and Hi-C sequencing, we generated a chromosome-level assembly of 4.09 Gb in span, scaffold N50 of 429 Mb, and complete BUSCO score of 98.1%, containing 10 pseudo-chromosomes. We provide Illumina datasets of males and females, used to identify the X chromosome. The assembly contains 19,034 predicted protein-coding genes, and a total of 75.21% of repetitive DNA sequences. By leveraging HiFi reads, we mapped the genome-wide distribution of methylated bases (5mC and 6 mA). This comprehensive assembly offers a robust reference for morabine grasshoppers and supports further research into speciation and sex chromosome diversification within the group and its related species.

Obstacle negotiation in female desert locust oviposition digging.

The female locust lays its eggs deep within soft substrate to protect them from predators and provide optimal conditions for successful development and hatching. During oviposition digging, the female's abdomen is pooled and extends into the ground, guided by a dedicated excavation mechanism at its tip, comprising two pairs of specialized digging valves. Little is known about how these active valves negotiate the various obstacles encountered on their path. In this study, female locusts oviposited their eggs in specialized sand-filled tubes with pre-inserted 3D-printed plastic obstacles. The subterranean route taken by the abdomen and digging valves upon encountering the obstacles was investigated, characterized, and compared to that in control tubes without obstacles. Data were obtained by way of visual inspection, by utilizing cone beam computed tomography scans in high-definition mode, and by making paraffin casts of the oviposition burrows (after egg hatching). We demonstrate, for the first time, the subterranean navigation ability of the female locust's excavation mechanism and its ability to circumvent obstacles during oviposition. Finally, we discuss the role of active sensory-motor mechanisms versus the passive embodied function of the valves, central control, and decision-making.

The grasshopper genome reveals long-term gene content conservation of the X Chromosome and temporal variation in X Chromosome evolution.

We present the first chromosome-level genome assembly of the grasshopper, Locusta migratoria, one of the largest insect genomes. We use coverage differences between females (XX) and males (X0) to identify the X Chromosome gene content, and find that the X Chromosome shows both complete dosage compensation in somatic tissues and an underrepresentation of testis-expressed genes. X-linked gene content from L. migratoria is highly conserved across seven insect orders, namely Orthoptera, Odonata, Phasmatodea, Hemiptera, Neuroptera, Coleoptera, and Diptera, and the 800 Mb grasshopper X Chromosome is homologous to the fly ancestral X Chromosome despite 400 million years of divergence, suggesting either repeated origin of sex chromosomes with highly similar gene content, or long-term conservation of the X Chromosome. We use this broad conservation of the X Chromosome to test for temporal dynamics to Fast-X evolution, and find evidence of a recent burst evolution for new X-linked genes in contrast to slow evolution of X-conserved genes.

SNMP1 is critical for sensitive detection of the desert locust aromatic courtship inhibition pheromone phenylacetonitrile.

BACKGROUND: Accurate detection of pheromones is crucial for chemical communication and reproduction in insects. In holometabolous flies and moths, the sensory neuron membrane protein 1 (SNMP1) is essential for detecting long-chain aliphatic pheromones by olfactory neurons. However, its function in hemimetabolous insects and its role for detecting pheromones of a different chemical nature remain elusive. Therefore, we investigated the relevance of SNMP1 for pheromone detection in a hemimetabolous insect pest of considerable economic importance, the desert locust Schistocerca gregaria, which moreover employs the aromatic pheromone phenylacetonitrile (PAN) to govern reproductive behaviors. RESULTS: Employing CRISPR/Cas-mediated gene editing, a mutant locust line lacking functional SNMP1 was established. In electroantennography experiments and single sensillum recordings, we found significantly decreased electrical responses to PAN in SNMP1-deficient (SNMP1-/-) locusts. Moreover, calcium imaging in the antennal lobe of the brain revealed a substantially reduced activation of projection neurons in SNMP1-/- individuals upon exposure to PAN, indicating that the diminished antennal responsiveness to PAN in mutants affects pheromone-evoked neuronal activity in the brain. Furthermore, in behavioral experiments, PAN-induced effects on pairing and mate choice were altered in SNMP1-/- locusts. CONCLUSIONS: Our findings emphasize the importance of SNMP1 for chemical communication in a hemimetabolous insect pest. Moreover, they show that SNMP1 plays a crucial role in pheromone detection that goes beyond long-chain aliphatic substances and includes aromatic compounds controlling reproductive behaviors.

Effect of RNAi mediated silencing of DIB, JHE, and CAM on the diapause termination of Calliptamus italicus (Orthoptera: Acrididae) eggs.

BACKGROUND: Calliptamus italicus L. is a major pest in Xinjiang grassland. The diapause overwintering strategy is one of the important reasons for the large population of this pest. This study investigated the function of the genes associated with the release of diapause (DIB, JHE and CAM) in Calliptamus italicus by RNA interference (RNAi) technology to aid in its biological control. RESULTS: The expression levels of DIB and its downstream-associated genes (EcR and FTZ-F1) in the eggs injected with dsDIB for 12 h decreased by 96.6%, 55.8% and 81.8%, respectively. Diapause began to terminate on day 3, and development was almost complete on day 6. However, the head was significantly smaller. The expression levels of JHE and its downstream-associated genes (JHEH and VgR) at 48 h after dsJHE treatment decreased by 76.5%, 85.6% and 85.9%, respectively. The termination of diapause occured on day 3 of incubation. The development was basically complete on day 6, but the yolk had been incompletely absorbed. The expression of CAM and its downstream-associated genes (CAMK4 and MYL) at 24 h after dsCAM treatment decreased by 42.4%, 95.3% and 82.7%, respectively. Diapause termination was completed on day 4 for incubation, and development was abnormal on day 6. The absorption of yolk was incomplete. CONCLUSION: DIB, JHE and CAM can delay the diapause termination of Calliptamus italicus eggs to different degrees and can be developed as potential target genes for its biological control. © 2024 Society of Chemical Industry.

Repetitive element expansions contribute to genome size gigantism in Pamphagidae: A comparative study (Orthoptera, Acridoidea).

Pamphagidae is a family of Acridoidea that inhabits the desert steppes of Eurasia and Africa. This study employed flow cytometry to estimate the genome size of eight species in the Pamphagidae. The results indicate that the genome size of the eight species ranged from 13.88 pg to 14.66 pg, with an average of 14.26 pg. This is the largest average genome size recorded for the Orthoptera families, as well as for the entire Insecta. Furthermore, the study explored the role of repetitive sequences in the genome, including their evolutionary dynamics and activity, using low-coverage next-generation sequencing data. The genome is composed of 14 different types of repetitive sequences, which collectively make up between 59.9% and 68.17% of the total genome. The Pamphagidae family displays high levels of transposable element (TE) activity, with the number of TEs increasing and accumulating since the family's emergence. The study found that the types of repetitive sequences contributing to the TE outburst events are similar across species. Additionally, the study identified unique repetitive elements for each species. The differences in repetitive sequences among the eight Pamphagidae species correspond to their phylogenetic relationships. The study sheds new light on genome gigantism in the Pamphagidae and provides insight into the correlation between genome size and repetitive sequences within the family.

Insect tracheal systems as inspiration for carbon dioxide capture systems.

Membrane technology advancements within the past twenty years have provided a new perspective on environmentalism as engineers design membranes to separate greenhouse gases from the environment. Several scientific journals have published articles of experimental evidence quantifying carbon dioxide (CO2), a common greenhouse gas, separation using membrane technology and ranking them against one another. On the other hand, natural systems such as the respiratory system of mammals also accomplish transmembrane transport of CO2. However, to our knowledge, a comparison of these natural organic systems with engineered membranes has not yet been accomplished. The tracheal respiratory systems of insects transport CO2at the highest rates in the animal kingdom. Therefore, this work compares engineered membranes to the tracheal systems of insects by quantitatively comparing greenhouse gas conductance rates. We demonstrate that on a per unit volume basis, locusts can transport CO2approximately ∼100 times more effectively than the best current engineered systems. Given the same temperature conditions, insect tracheal systems transport CO2three orders of magnitude faster on average. Miniaturization of CO2capture systems based on insect tracheal system design has great potential for reducing cost and improving the capacities of industrial CO2capture.

Serotonergic amplification of odor-evoked neural responses maps onto flexible behavioral outcomes.

Behavioral responses to many odorants are not fixed but are flexible, varying based on organismal needs. How such variations arise and the role of various neuromodulators in achieving flexible neural-to-behavioral mapping is not fully understood. In this study, we examined how serotonin modulates the neural and behavioral responses to odorants in locusts (Schistocerca americana). Our results indicated that serotonin can increase or decrease appetitive behavior in an odor-specific manner. On the other hand, in the antennal lobe, serotonergic modulation enhanced odor-evoked response strength but left the temporal features or the combinatorial response profiles unperturbed. This result suggests that serotonin allows for sensitive and robust recognition of odorants. Nevertheless, the uniform neural response amplification appeared to be at odds with the observed stimulus-specific behavioral modulation. We show that a simple linear model with neural ensembles segregated based on behavioral relevance is sufficient to explain the serotonin-mediated flexible mapping between neural and behavioral responses.

Asymmetry between the dorsal and ventral digging valves of the female locust: function and mechanics.

BACKGROUND: The female locust is equipped with unique digging tools, namely two pairs of valves-a dorsal and a ventral-utilized for excavating an underground hole in which she lays her eggs. This apparatus ensures that the eggs are protected from potential predators and provides optimal conditions for successful hatching. The dorsal and the ventral valves are assigned distinct roles in the digging process. Specifically, the ventral valves primarily function as anchors during propagation, while the dorsal valves displace soil and shape the underground tunnel. RESULTS: In this study, we investigated the noticeable asymmetry and distinct shapes of the valves, using a geometrical model and a finite element method. Our analysis revealed that although the two pairs of valves share morphological similarities, they exhibit different 3D characteristics in terms of absolute size and structure. We introduced a structural characteristic, the skew of the valve cross-section, to quantify the differences between the two pairs of valves. Our findings indicate that these structural variations do not significantly contribute to the valves' load-bearing capabilities under external forces. CONCLUSIONS: The evolutionary development of the form of the female locust digging valves is more aligned with fitting their respective functions rather than solely responding to biomechanical support needs. By understanding the intricate features of these locust valves, and using our geometrical model, valuable insights can be obtained for creating more efficient and specialized tools for various digging applications.

Ring-shaped odor coding in the antennal lobe of migratory locusts.

The representation of odors in the locust antennal lobe with its >2,000 glomeruli has long remained a perplexing puzzle. We employed the CRISPR-Cas9 system to generate transgenic locusts expressing the genetically encoded calcium indicator GCaMP in olfactory sensory neurons. Using two-photon functional imaging, we mapped the spatial activation patterns representing a wide range of ecologically relevant odors across all six developmental stages. Our findings reveal a functionally ring-shaped organization of the antennal lobe composed of specific glomerular clusters. This configuration establishes an odor-specific chemotopic representation by encoding different chemical classes and ecologically distinct odors in the form of glomerular rings. The ring-shaped glomerular arrangement, which we confirm by selective targeting of OR70a-expressing sensory neurons, occurs throughout development, and the odor-coding pattern within the glomerular population is consistent across developmental stages. Mechanistically, this unconventional spatial olfactory code reflects the locust-specific and multiplexed glomerular innervation pattern of the antennal lobe.

Bioaccessibility of trace elements and Fe and Al endogenic nanoparticles in farmed insects: Pursuing quality sustainable food.

This study investigated the in vitro bioaccessibility of aluminum, copper, iron, manganese, lead, selenium, and zinc in three important species of farmed insects: the yellow mealworm (Tenebrio molitor), the house cricket (Acheta domesticus) and the migratory locust (Locusta migratoria). Results show that all three insect species constitute excellent sources of essential elements (Fe, Cu and Zn) for the human diet, contributing to the recommended dietary allowance, i.e., 10%, 50%, and 92%, respectively. A higher accumulation of Se (≥1.4 mg Se/kg) was observed with increasing exposure concentration in A. domesticus, showing the possibility of using insects as a supplements for this element. The presence of Al and Fe nanoparticles was confirmed in all three species using single particle-inductively coupled plasma-mass spectrometry and transmission electron microscopy. The results also indicate that Fe bioaccessibility declines with increasing Fe-nanoparticle concentration. These findings contribute to increase the nutritional and toxicological insights of farmed insects.

Synergistic olfactory processing for social plasticity in desert locusts.

Desert locust plagues threaten the food security of millions. Central to their formation is crowding-induced plasticity, with social phenotypes changing from cryptic (solitarious) to swarming (gregarious). Here, we elucidate the implications of this transition on foraging decisions and corresponding neural circuits. We use behavioral experiments and Bayesian modeling to decompose the multi-modal facets of foraging, revealing olfactory social cues as critical. To this end, we investigate how corresponding odors are encoded in the locust olfactory system using in-vivo calcium imaging. We discover crowding-dependent synergistic interactions between food-related and social odors distributed across stable combinatorial response maps. The observed synergy was specific to the gregarious phase and manifested in distinct odor response motifs. Our results suggest a crowding-induced modulation of the locust olfactory system that enhances food detection in swarms. Overall, we demonstrate how linking sensory adaptations to behaviorally relevant tasks can improve our understanding of social modulation in non-model organisms.

Parental experiences orchestrate locust egg hatching synchrony by regulating nuclear export of precursor miRNA.

Parental experiences can affect the phenotypic plasticity of offspring. In locusts, the population density that adults experience regulates the number and hatching synchrony of their eggs, contributing to locust outbreaks. However, the pathway of signal transmission from parents to offspring remains unclear. Here, we find that transcription factor Forkhead box protein N1 (FOXN1) responds to high population density and activates the polypyrimidine tract-binding protein 1 (Ptbp1) in locusts. FOXN1-PTBP1 serves as an upstream regulator of miR-276, a miRNA to control egg-hatching synchrony. PTBP1 boosts the nucleo-cytoplasmic transport of pre-miR-276 in a "CU motif"-dependent manner, by collaborating with the primary exportin protein exportin 5 (XPO5). Enhanced nuclear export of pre-miR-276 elevates miR-276 expression in terminal oocytes, where FOXN1 activates Ptbp1 and leads to egg-hatching synchrony in response to high population density. Additionally, PTBP1-prompted nuclear export of pre-miR-276 is conserved in insects, implying a ubiquitous mechanism to mediate transgenerational effects.

Theoretical principles explain the structure of the insect head direction circuit.

To navigate their environment, insects need to keep track of their orientation. Previous work has shown that insects encode their head direction as a sinusoidal activity pattern around a ring of neurons arranged in an eight-column structure. However, it is unclear whether this sinusoidal encoding of head direction is just an evolutionary coincidence or if it offers a particular functional advantage. To address this question, we establish the basic mathematical requirements for direction encoding and show that it can be performed by many circuits, all with different activity patterns. Among these activity patterns, we prove that the sinusoidal one is the most noise-resilient, but only when coupled with a sinusoidal connectivity pattern between the encoding neurons. We compare this predicted optimal connectivity pattern with anatomical data from the head direction circuits of the locust and the fruit fly, finding that our theory agrees with experimental evidence. Furthermore, we demonstrate that our predicted circuit can emerge using Hebbian plasticity, implying that the neural connectivity does not need to be explicitly encoded in the genetic program of the insect but rather can emerge during development. Finally, we illustrate that in our theory, the consistent presence of the eight-column organisation of head direction circuits across multiple insect species is not a chance artefact but instead can be explained by basic evolutionary principles.

Insects, including fruit flies and locusts, move throughout their environment to find food, interact with each other or escape danger. To navigate their surroundings, insects need to be able to keep track of their orientation. This tracking is achieved through visual cues and integrating information about their movements whilst flying so they know which direction their head is facing. The set of neurons responsible for relaying information about the direction of the head (also known as heading) are connected together in a ring made up of eight columns of cells. Previous studies showed that the level of activity across this ring of neurons resembles a sinusoid shape: a smooth curve with one peak which encodes the animal's heading. Neurons downstream from this eight-column ring, which relay velocity information, also display this sinusoidal pattern of activation. Aceituno, Dall'Osto and Pisokas wanted to understand whether this sinusoidal pattern was an evolutionary coincidence, or whether it offers a particular advantage to insects. To answer this question, they established the mathematical criteria required for neurons in the eight-column ring to encode information about the heading of the animal. This revealed that these conditions can be satisfied by many different patterns of activation, not just the sinusoidal shape. However, Aceituno, Dall'Osto and Pisokas show that the sinusoidal shape is the most resilient to variations in neuronal activity which may impact the encoded information. Further experiments revealed that this resilience only occurred if neurons in the circuit were connected together in a certain pattern. Aceituno, Dall'Osto and Pisokas then compared this circuit with experimental data from locusts and fruit flies and found that both insects exhibit the predicted connection pattern. They also discovered that animals do not have to be born with this neuronal connection pattern, but can develop it during their lifetime. These findings provide fresh insights into how insects relay information about the direction of their head as they fly. They suggest that the structure of the neuronal circuit responsible for encoding head direction was not formed by chance but instead arose due to the evolutionary benefits it provided.

From bristle to brain: embryonic development of topographic projections from basiconic sensilla in the antennal nervous system of the locust Schistocerca gregaria.

The antennal flagellum of the locust S. gregaria is an articulated structure bearing a spectrum of sensilla that responds to sensory stimuli. In this study, we focus on the basiconic-type bristles as a model for sensory system development in the antenna. At the end of embryogenesis, these bristles are found at fixed locations and then on only the most distal six articulations of the antenna. They are innervated by a dendrite from a sensory cell cluster in the underlying epithelium, with each cluster directing fused axons topographically to an antennal tract running to the brain. We employ confocal imaging and immunolabeling to (a) identify mitotically active sense organ precursors for sensory cell clusters in the most distal annuli of the early embryonic antenna; (b) observe the subsequent spatial appearance of their neuronal progeny; and (c) map the spatial and temporal organization of axon projections from such clusters into the antennal tracts. We show that early in embryogenesis, proliferative precursors are localized circumferentially within discrete epithelial domains of the flagellum. Progeny first appear distally at the antennal tip and then sequentially in a proximal direction so that sensory neuron populations are distributed in an age-dependent manner along the antenna. Autotracing reveals that axon fasciculation with a tract is also sequential and reflects the location and age of the cell cluster along the most distal annuli. Cell cluster location and bristle location are therefore represented topographically and temporally within the axon profile of the tract and its projection to the brain.