effect of terpenoids in pest incidence in crop plants?

Answer 1

There are so many terpenoids in so many different plants that it's hard to answer your question. Some terpenoids attract insects, some repel insects, some attract predators to feed on crop eating insects.

Answer 2

Your question is somewhat vague, so I'm guessing that what your are asking is "does the presence of terpenoids in crop plants affect the occurrence of feeding by certain insects?" The answer is yes. But without more information about which crop plant, which terpenoid and which pest, I can't be of more help to you. Plants are amazing creatures. They can't run and hide from their enemies so they have just had to stand and fight over the eons of history. The ones that had genetic variability to produce certain chemicals such as terpenoids had better tools to fight certain pests. The array of defensive chemicals that plants have developed is awesome. Terpenoids are just one such example. One of the problems with selecting crop plants for more natural defenses is that in some cases, since we, especially vegetarians, are natural enemies of plants, the increased natural defense chemicals make them taste bad to us. Therefore, we select plants with less defensive chemicals which taste better to us. The problem is, they may taste better or be less toxic to plant pests too, therefore suffer more damage. We in the plant sciences seek a balance. Plants act only in their own favor.

Answer 3

The terpenoids, sometimes referred to as isoprenoids, are a large and diverse class of naturally occurring organic chemicals similar to terpenes, derived from five-carbon isoprene units assembled and modified in thousands of ways. Most are multicyclic structures which differ from one another not only in functional groups, but also in their basic carbon skeletons. These lipids can be found in all classes of living things, and are the largest group of natural products.

Plant terpenoids are extensively used for their aromatic qualities. They play a role in traditional herbal remedies and are under investigation for antibacterial, antineoplastic and other pharmaceutical effects. Terpenoids contribute to the scent of eucalyptus, the flavors of cinnamon, cloves and ginger and the color of yellow flowers. Well-known terpenoids include citral, menthol, camphor and the cannabinoids found in the Cannabis plant.

The steroids and sterols in animals are biologically produced from terpenoid precursors. Sometimes terpenoids are added to proteins, e.g. to enhance their attachment to the cell membrane; this is known as isoprenylation.

Terpenes are hydrocarbons resulting from the combination of several isoprene units. Terpenoids can be thought of as modified terpenes, where methyl groups have been moved or removed, or oxygen atoms added. (Some authors use the term "terpene" more broadly, to include the terpenoids.) Just like terpenes, the terpenoids can be classified according to the number of isoprene units used:

Monoterpenoids, 2 isoprene units
Sesquiterpenoids, 3 isoprene units
Diterpenoids, 4 isoprene units
Sesterterpenoids, 5 isoprene units
Triterpenoids, 6 isoprene units
Tetraterpenoids, 8 isoprene units
Polyterpenoids with a larger number of isoprene units
Terpenoids can also be classified according to the number of cyclic structures they contain