Jennifer S. Sun

Drosophila suzukii (spotted-wing drosophila) is an invasive pest that infests ripe, market-ready fruit, posing a significant threat to fruit production. To develop alternatives to conventional chemical control, environmentally derived fungi (EF) were evaluated for their potential to modulate D. suzukii behavior and viability. Pichia occidentalis , isolated from Drosophila melanogaster oral and fecal secretions, exhibited species-specific repellency in D. suzukii . In D. suzukii , exposure to P. occidentalis reduced survival, most pronounced in males, and significantly inhibited female oviposition. In contrast, D. melanogaster showed no reduction in survival and increased oviposition in the presence of the fungus. Solid-phase microextraction coupled with gas chromatography–mass spectrometry (SPME GC-MS) identified volatile metabolites produced by P. occidentalis . Subsequent cafeteria-style assays of individual volatiles revealed that several of these compounds elicited aversive responses in D. suzukii while remaining attractive to D. melanogaster , highlighting species-specific olfactory effects. Isoamyl butanoate, 2-phenyl-1-propanal, and benzyl alcohol demonstrated consistent repellent activity with superior efficacy compared to established D. suzukii repellents (2-pentylfuran, 1-octen-3-ol, and geosmin). Collectively, these findings demonstrate that EF metabolites can differentially influence closely related species and may be leveraged as targeted, behavior-based tools for managing D. suzukii . IMPORTANCE: Drosophila suzukii is a major invasive pest that damages fresh fruit by laying eggs in ripening crops, leading to significant agricultural losses. Current control strategies rely heavily on chemical insecticides, which provide incomplete control and can harm non-target organisms. Here, we show that volatile metabolites produced by the environmental yeast Pichia occidentalis differentially influence closely related Drosophila species, decreasing oviposition and longevity in D. suzukii while stimulating oviposition in D. melanogaster . This species-specific divergence highlights the potential of microbial volatiles as precision tools for pest management, further supporting a behavior-based approach that selectively disrupts pest reproduction while minimizing ecological impact.

Spotted wing drosophila (Drosophila suzukii; SWD) has become a globally invasive pest by ovipositing in ripening, intact fruit rather than decaying material, a niche distinct from most other drosophilids. An expanding body of work implicates microbes and microbially derived chemistry as key drivers of this ecology, shaping fly biology across life stages. However, much of this evidence is derived from microbiome surveys and observational comparisons, further constrained by uncontrolled diet history, laboratory rearing, and insufficient ecological context. We examine how the SWD microbiome differs in which taxa are present (composition), how flies pick up those taxa from fruit and maternal sources (acquisition), how long those taxa are retained across life stages (persistence), and how each of these varies with diet, geography, season, and host crops. We then address how microbial cues and fermentation state function as context-dependent drivers of adult attraction, avoidance, and oviposition, and how microbe-mediated interspecific interactions reshape substrate suitability and competition among drosophilids. Throughout, we critically evaluate experimental designs and identify gaps that impede causal inference. These include limited strain-level resolution, incomplete fungal characterization, and weak linkages between microbial community structure and host phenotypes. Key unresolved questions include how SWD maintains performance across diverse hosts, how microbes modulate sensory processing during seasonal shifts, and which microbial metabolites drive attraction, avoidance, and competition. Resolving these questions is a direct prerequisite for field-stable integrated pest management (IPM), including microbially informed behavioral lures, oviposition deterrents derived from pathogen- and competitor-associated volatiles, and competitor-mediated suppression strategies. The experimental priorities identified here translate directly into a roadmap for the next generation of mechanistically grounded, ecologically realistic SWD management tools.

Chemosensory systems are crucial for insect survival, enabling host-seeking, food acquisition, and oviposition site selection. While insect-associated microbes are known to influence host development and immunity, their role in modulating chemosensory behavior remains poorly understood. Here, we show that mono-association with Escherichia coli alters sensory-driven behaviors in both larval and adult axenic Drosophila melanogaster. In larvae, E. coli mono-association altered phototaxis and mechanosensory responses across genotypes, while changes in tunneling and thermosensory behaviors were reduced or absent in ionotropic receptor (IR) co-receptor mutants. In adults, E. coli mono-association increased attraction to fermentation cues (apple cider vinegar, ethanol) and enhanced sucrose consumption in wild-type and Orco-deficient flies, whereas these effects were reduced or absent in IR co-receptor mutants (IR25a⁻ and IR76b⁻). Together, these findings indicate that under defined gnotobiotic conditions, E. coli exposure alters sensory-driven behavioral outputs relative to axenic controls. Effects are reduced or absent in IR co-receptor mutants, consistent with a role for IR pathways in mediating these behavioral shifts. These findings support a role for microbial cues in shaping insect sensory-driven behaviors and highlight the importance of microbial status in interpreting behavioral phenotypes. This work provides a framework for future studies investigating how microbial signals interact with conserved sensory pathways.

Insect pests impose major economic, agricultural, and public health burdens, damaging crops and transmitting pathogens such as dengue, malaria, and Zika. Conventional chemical control is increasingly ineffective due to insecticide resistance and environmental concerns, prompting a search for innovative strategies. The insect microbiome—comprising both obligate symbionts and environmentally acquired microbes—emerges as a key driver of host physiology and behavior. Microbes influence nutrient acquisition, immunity, reproduction, and chemosensory processing, often to promote their own transmission. By modulating olfactory and gustatory pathways, microbiota can alter host-seeking, mate choice, foraging, and oviposition patterns, reshaping ecological interactions and vector dynamics. These effects are shaped by microbial acquisition routes, habitat conditions, and anthropogenic pressures such as pesticide use, pollution, and climate change. Understanding these multi-directional interactions offers opportunities to design highly specific, microbe-based insect control strategies, from deploying microbial metabolites that disrupt host sensory systems to restoring beneficial symbionts in threatened pollinators. Integrating microbiome ecology with insect physiology and behavior not only deepens our understanding of host–microbe coevolution but also enables the development of sustainable, targeted alternatives to chemical insecticides. This review synthesizes current evidence linking microbiomes to insect biology and explores their potential as tools for pest and vector management.

The annual spring meeting for the Theobald Smith Society was held in May 2025 on the campus of Rutgers University—New Brunswick, as part of a 2-day celebration of microbiology discovery in New Jersey. A total of 140 branch members from across New Jersey attended the meeting, composed of undergraduate, graduate, and postdoctoral trainees, faculty members, and government and industry professionals. This report highlights the breadth and diversity of research conducted by members of the American Society for Microbiology in the Theobald Smith Society and celebrates their groundbreaking discoveries.

Chemosensory systems are critical for insect survival, enabling host seeking, food acquisition, and oviposition site selection. While insect-associated microbes are known to influence host development and immunity, their role in modulating chemosensory behavior remains poorly understood. Here, we demonstrate that Escherichia coli , a bacterium identified in non-gut tissues of Aedes albopictus and experimentally reintroduced into axenic Drosophila melanogaster , alters both larval and adult sensory-driven behaviors. In larvae, E. coli infection modified phototaxis and mechanosensory responses across genotypes, while tunneling and thermosensory behaviors were specifically dependent on the ionotropic receptor co-receptor IR25a. In adults, E. coli increased attraction to fermentation cues (apple cider vinegar, ethanol) and enhanced sucrose consumption in wild-type and Orco -deficient flies, but not in IR25a -deficient mutants. Gas chromatography–mass spectrometry revealed that E. coli shifted cuticular hydrocarbon composition toward shorter-chain alkanes and increased the sex pheromone 9-tricosene in an IR25a-dependent manner. Together, these findings show that E. coli broadly reprograms insect sensory behavior, with IR25a serving as a critical mediator of microbial influence on chemosensory and physiological traits. This work identifies a previously unrecognized role for E. coli in shaping insect behavior and chemical ecology, providing a foundation for investigating microbial contributions to host–microbe coevolution and for exploring microbial cues as novel, environmentally sustainable tools for insect control. Importance: Insects depend on their sense of smell and taste to find food, mates, and safe places to reproduce. These behaviors drive the spread of insect-borne diseases and cause major agricultural losses worldwide. Our work shows that a common bacterium, Escherichia coli , can reshape insect sensory behaviors, influencing how flies respond to light, temperature, food, and even the chemical signals on their outer surface that control mating. Importantly, these effects are linked to a specific sensory receptor, IR25a, which is conserved across many insect species. This finding reveals a previously unknown role for microbes in fine-tuning insect behavior. Understanding how bacteria influence insect sensory systems not only provides insight into host–microbe interactions but also opens the door to new, environmentally friendly ways of managing insect pests by targeting their behavior rather than killing them outright.

The annual fall meeting for the Theobald Smith Society was held in November 2024 on the campus of Rutgers University—New Brunswick. Eighty-six branch members from across New Jersey attended the meeting, composed of undergraduate, graduate, and postdoctoral trainees, faculty members, and government and industry professionals. This report highlights the breadth and diversity of research conducted by American Society for Microbiology members in the Theobald Smith Society and celebrates their groundbreaking discoveries.

SUMMARY: The bacterial cell-cell communication process called quorum sensing enables groups of bacteria to synchronously alter behavior in response to changes in cell population density. Quorum sensing relies on the production, release, accumulation, and detection of extracellular signal molecules called autoinducers. Here, we investigate a mechanism employed by a vibriophage to surveil host quorum sensing and tune its lysogeny-lysis decision to host cell density. The phage possesses a gene called vqmA _Phage encoding a quorum-sensing receptor homologous to vibrio VqmA. Both VqmA receptors can detect the host bacteria-produced autoinducer called DPO. DPO-bound VqmA _Phage launches the phage lysis process. We discover that the bacterial host produces an inducer of the VqmA _Phage -directed quorum-sensing lysogeny-lysis transition. Production of the inducer appears to be widespread among bacteria. A screen of the Escherichia coli Keio collection for mutants impaired for inducer production revealed lomR , located in a prophage, and encoding a poorly understood protein. In the E. coli screening strain, lomR is interrupted by DNA encoding an insertion element. The 3’ domain of this LomR protein is sufficient to induce VqmA _Phage -directed lysis. Alanine-scanning mutagenesis showed that substitution at either of two key residues abrogates inducer activity. Full-length LomR is similar to the outer membrane porin OmpX in E. coli and Vibrio parahaemolyticus O3:K6, and OmpT in Vibrio cholerae C6706, and indeed, OmpX and OmpT can induce VqmA _Phage -directed activity. Possibly, development of the LomR, OmpX, or OmpT proteins as tools to direct phage lysis of host cells could be used to control bacteria in medical or industrial settings. ABSTRACT IMPORTANCE: Bacteria communicate with chemical signal molecules using a process called quorum sensing. Quorum sensing allows bacteria to track their cell numbers and orchestrate collective behaviors. Recently, we discovered that a virus that infects and kills bacteria “eavesdrops” on its host’s quorum-sensing process. Specifically, the virus monitors host cell growth by detecting the accumulation of host quorum-sensing signal molecules. In response to the garnered quorum-sensing information, the virus kills the host bacterial cells when the bacterial population has reached a high cell density. This strategy presumably enhances transmission of viruses to new host cells. Here, we discover and characterize three closely-related bacterial host-produced proteins called LomR, OmpX, and OmpT that are capable of inducing the viral quorum-sensing-mediated killing program. Development of this class of inducer proteins as tools to drive “on demand” virus-mediated lysis of pathogenic host bacterial cells could be used to control bacteria in medical or industrial settings.

Odorant binding proteins (Obps) are expressed at extremely high levels in the antennae of insects, and have long been believed essential for carrying hydrophobic odorants to odor receptors. Previously we found that when one functional type of olfactory sensillum in Drosophila was depleted of its sole abundant Obp, it retained a robust olfactory response (Larter et al., 2016). Here we have deleted all the Obp genes that are abundantly expressed in the antennal basiconic sensilla. All of six tested sensillum types responded robustly to odors of widely diverse chemical or temporal structure. One mutant gave a greater physiological and behavioral response to an odorant that affects oviposition. Our results support a model in which many sensilla can respond to odorants in the absence of Obps, and many Obps are not essential for olfactory response, but that some Obps can modulate olfactory physiology and the behavior that it drives.

The Drosophila wing was proposed to be a taste organ more than 35 years ago, but there has been remarkably little study of its role in chemoreception. We carry out a differential RNA-seq analysis of a row of sensilla on the anterior wing margin and find expression of many genes associated with pheromone and chemical perception. To ask whether these sensilla might receive pheromonal input, we devised a dye-transfer paradigm and found that large, hydrophobic molecules comparable to pheromones can be transferred from one fly to the wing margin of another. One gene, Ionotropic receptor (IR)52a, is coexpressed in neurons of these sensilla with fruitless, a marker of sexual circuitry; IR52a is also expressed in legs. Mutation of IR52a and optogenetic silencing of IR52a⁺ neurons decrease levels of male sexual behavior. Optogenetic activation of IR52a⁺ neurons induces males to show courtship toward other males and, remarkably, toward females of another species. Surprisingly, IR52a is also required in females for normal sexual behavior. Optogenetic activation of IR52a⁺ neurons in mated females induces copulation, which normally occurs at very low levels. Unlike other chemoreceptors that act in males to inhibit male–male interactions and promote male–female interactions, IR52a acts in both males and females, and can promote male–male as well as male–female interactions. Moreover, IR52a⁺ neurons can override the circuitry that normally suppresses sexual behavior toward unproductive targets. Circuit mapping and Ca²⁺ imaging using the trans-Tango system reveals second-order projections of IR52a⁺ neurons in the subesophageal zone (SEZ), some of which are sexually dimorphic. Optogenetic activation of IR52a⁺ neurons in the wing activates second-order projections in the SEZ. Taken together, this study provides a molecular description of the chemosensory sensilla of a greatly understudied taste organ and defines a gene that regulates the sexual circuitry of the fly.