Coevolution between plants and herbivores has been proposed as a major evolutionary force that resulted in their radiation and diversification. Plants have evolved a broad array of strategies that directly or indirectly avoid, repel, deter, or kill herbivore attackers. These include (but not limited to) tolerance to damage through compensatory growth of tissue lost from herbivory, resistance via physical and chemical defenses, induced responses, and avoidance through reduced apparency or phenological mismatch. In response, herbivores have evolved adaptations to circumvent, resist, detoxify, and even use plant defenses for their own benefit (e.g. sequestration). These include anatomical, physiological, and behavioral adaptations, but also symbiotic associations to overcome the defenses of the host plant. Ecologists and evolutionary biologists have been studying plant–herbivore interactions for decades. Recent advances in community ecology, genomics, metabolomics, and transgenic approaches allowed us to uncover the mechanisms by which some herbivores acquired the ability to neutralize plant defenses, or how plant communities reduce herbivory by creating heterogeneous chemical landscapes. Future research should consider integrating trait syndromes rather than individual traits when testing hypotheses about plant–insect coevolution, and including the third trophic level as an important selective force in plant–herbivore coevolution.
Aromatic amino acids (AAA) are essential for insect development and survival, serving as precursors for cuticle formation, immune defenses, and neurotransmitter synthesis. Because insect genomes lack the shikimate pathway, they must obtain AAA from external sources, raising the question of how microorganisms contribute to host AAA availability. Here, we review evidence spanning the continuum of insect–microbe associations, from obligate intracellular symbioses to diverse gut microbial communities. Comparative genomics reveals the repeated retention of shikimate and AAA biosynthetic pathways in intracellular symbionts despite extensive genome reduction, while experimental studies demonstrate that symbiont-derived AAA directly support cuticle maturation, desiccation resistance, and overall host performance. Similar nutritional roles are increasingly suspected in specialized extracellular gut symbioses, suggesting functional convergence between distinct organizational frameworks. Beyond these highly integrated associations, growing evidence indicates that gut microbiota may also influence host AAA homeostasis. Although direct microbial AAA provisioning remains difficult to demonstrate, microbiota disruption consistently affects AAA-dependent traits, including cuticle melanization and neurotransmitter-mediated behaviors. These effects are reinforced by experimental inhibition of microbial AAA biosynthesis. Together, these observations support the view that AAA are a central metabolic currency between insects and their microbial partners, with important consequences for insect physiology, fitness, and adaptation.
Biological invasions frequently disrupt co-evolved host–parasitoid interactions and create evolutionary traps in which native parasitoids attack unsuitable invasive hosts. While escape from such traps has traditionally been viewed as a consequence of adaptive evolution, recent studies suggest that ecological interactions among parasitoids may also enable exploitation of otherwise unsuitable hosts. In particular, increasing evidence supports the occurrence of ‘pirate parasitism’, a specialized form of kleptoparasitism in which one parasitoid species enables another to successfully develop in an otherwise unsuitable host, often through host immune suppression. Here, we review historical and recent studies on pirate parasitism, clarify its conceptual framework, and discuss its ecological and evolutionary implications. Reported cases include both native sympatric systems and invasion-associated systems, suggesting that pirate parasitism may transiently expand realized host ranges, alleviate demographic costs of maladaptive oviposition, and potentially promote rewiring of host–parasitoid interaction networks. We further discuss the possibility that pirate parasitism functions as an ecological bridge between initial maladaptive host use and subsequent evolutionary host range expansion. Finally, we highlight major knowledge deficiencies, including limited evidence from natural ecosystems and unresolved behavioral and physiological mechanisms underlying pirate parasitism. Understanding kleptoparasitic interactions among parasitoids may provide new insights into eco-evolutionary dynamics in rapidly changing environments.
The gut is one of the largest internal organs in animals and is central to nutrition. Its need to uptake food from the environment implies it is open at both ends, exposing its lumen to the outside world and to colonization by ingested microbial communities. As the primary site of host-associated microbiota, the gut has, over evolutionary time, fostered stable associations with specific microbes to which the host has delegated key biological functions. Insect gut microbiota is of interest both for its impact on this ecologically important animal group and as a simplified model for understanding fundamental features of host-microbiota interactions. Here, we focus on the highly distinctive midgut of phytophagous stinkbugs (Heteroptera: Pentatomomorpha) and their associated microbiota. The most distinctive feature of the midgut is a posterior crypt-bearing region that constitutes a symbiotic organ housing a single specific bacterial symbiont population. The anterior gut harbors a more diverse microbial community. In many species, like Riptortus pedestris, microbe-free newborns ingest bacteria by soil probing and gradually filter them along the anterior to posterior gut axis. The process enriches Burkholderia sensu lato until a single Caballeronia strain is established in the crypt region. We describe the selective conditions in the gut and the reciprocal symbiont traits that precisely and reproducibly shape the gut microbiota from a variable soil community. Even if the process is accurate, it is, however, not without vulnerabilities because it enriches Burkholderia in the gut, comprising many pathogenic strains. The Caballeronia crypt symbionts and some pathogen strains can be exploited by the host to reinforce its immunity, but other strains cause deadly infections.
