Feeding attraction and deterrence

Many sesquiterpenes which are not highly oxygenated are also found in essential oils. Several of these are reported to possess activity. a-Farnesene from apples is an attractant and oviposition stimulant for the codling moth ( ) and farnesol has been demonstrated to be an active feeding deterrent to gypsy moth larvae (Lymontria dispar) (69). 

Ironically, terpenes serve both as major deterrents to feeding and as attractants for animals (Hedin et al., 1974). Volatile compounds are often involved in long-distance interactions and are especially important as attractants and repellents (Kogan, 1975). 

Hedin, P. a., F. G. Maxwell, and J. N. Jenkins, Insect plant attractants, feeding stimulants, repellents, deterrents, and other related factors affecting insect behavior, r/i Proc. Summer Inst. Biol. Control of Plant Insects and Diseases (F. G. Maxwell and F. A. Harris, eds.), 494-557, University of Mississippi Press, Jackson, 1974. 

Peramine (352) is a pyrrole alkaloid identified as a major insect feeding deterrent isolated from perennial ryegrass infected with the entophyte Acre-monium lolii. Due to the interesting heterocyclic ring system and biological activity, the synthesis of peramine is attractive [230],... 

Insect preferences for certain types of food can be considered from a chemical ecological point of view as follows presence of attractant, fixing factor oviposition-stimulant, and feeding stimulant absence of repellent, oviposition deterrent, feeding deterrent, nutritional defect, and growth-deterrent. Conversely, the opposite is true for certain food types undisturbed by insects. 

There has been considerable progress in isolating and identifying compounds that affect Insect behaviour. A recent review contains more than 800 references to the literature and lists over 300 compounds as insect attractants, attractant pheromones and related compounds together with the corresponding insect species (26). Other pheromones (trail pheromones, hair pencil secretions, etc.), feeding deterrents, ovipositlon deterrents, an other types of behavioural compounds are not included in this comprehensive review, but the volume of Information on behavioural compounds is constantly being expanded as new compounds are identified. 

Figure 5.1 Examples of terpenoids that are of commercial importance or whose functional role in plants has recently been investigated. Isoprene may stabilize membranes at high temperatures. Camphor, artemisinin and paclitaxel (taxol) are valuable pharmaceuticals. The other three compounds appear to be involved in plant defence pulegone is toxic to herbivores polygodial is a herbivore feeding deterrent and (3 )-4,8-dimethyl-1,3,7-nonatriene, a Cn homoterpene, functions to attract herbivore enemies to herbivore-damaged plants.

Essential oils demonstrate a wide range of bioactivities from direct toxicity to insects, microorganisms and plants, to oviposition and feeding deterrence as well as repellence and attraction. How these effects are mediated is still being... 

---