What do trees produce that can have toxic and deterrent effects on certain insects?

Trees produce allelochemicals, which are organic compounds that can influence the behavior and physiology of insects and other organisms. These substances play a crucial role in a tree's defense mechanisms against herbivory. By generating allelochemicals, trees can deter certain insects from feeding on them, either through toxicity or by causing undesirable effects that make the tree less palatable or attractive.

These compounds can vary widely in their structure and function, and might include secondary metabolites like phenolics, terpenes, and alkaloids. The production of allelochemicals allows trees not only to defend themselves but also to interact with their surrounding ecosystem, influencing pest populations and promoting biodiversity.

In contrast, while starches are primarily energy storage compounds, resins can act as physical barriers and may contain some deterrent properties, and oils may have aromatic or antifungal properties, they are not specifically linked to the direct toxic and deterrent effects on insects in the same manner as allelochemicals. This distinction highlights the unique role that allelochemicals play in plant-insect interactions, especially regarding tree defenses.