a) Toxins or digestibility reducing factors: These disrupt growth and development of insects and reduce the longevity of adults. For example; antibiotics.
b) Repellents: These disrupt normal host selection behaviour. These cause insects to orient their movements away from a source and are applied to the surface to derive insects away. Repellents are generally volatile substances which are sensed by the insects causing them to fly or crawl away.
c) Feeding deterrents: These chemicals donot cause the movement away from their food but prevent feeding or oviposition. These are significant in host-plant interactions.
- Plants producing allomones:
1. Desmodium (tick-trefoils)
Allomones serve as repellents. The allomones released by plants repel, deter or harm many phytophagous insects. Thus, these are applied to the crops as insect repellents or feeding deterrents protecting them from the insect infestation.