Tropical dry deciduous forests (TDFs) experience pronounced wet–dry cycles that change leaf availability, tissue age, plant traits, and insect activity. This seasonality provides a useful setting for examining when plants and insects interact, but direct mechanistic evidence is uneven across regions and taxa. This focused narrative review synthesizes field studies from southern India, Mexico, and Brazil alongside broader research on chemical ecology, climate effects, and dry-forest conservation. Field studies show that leaf flushing may precede the rains, herbivore activity can increase after rain onset, and evergreen trees may provide dry-season resources. Leaf age, phenology, physical defenses, and foliar phenolics are associated with herbivory, although effects vary among species and sites. One community-level study used plant–volatile associations and plant–herbivore records to develop an information-theory framework; it supports a testable explanation of chemical communication, not a universal arms-race rule. Mexican gall studies also associate gall presence with altered foliar phenolics and lower folivore damage on some hosts, without establishing causation. Warming, drought, altered rainfall timing, and fragmentation could shift plant resources and insect activity at different rates, but current evidence does not demonstrate a general climate-driven mismatch in TDFs. Because estimates of dry-forest extent depend on biome definitions, conservation figures are interpreted with their underlying assumptions. We conclude that repeated, place-based studies linking phenology, plant traits, insect behavior, and natural enemies are needed to identify vulnerable interactions and inform conservation.