Nicotine insects’ response

An illustration of the variable responses to nicotine concerns aphids. In an experiment, 2 per cent of an insect population died or became moribund when exposed to 0.0001 M nicotine solution, 48 per cent were affected when the concentration was 0.0025 M, and 98.5 per cent when the concentration was 0.012 M. The concentrations of nicotine required to affect all the insects alike varied more than 120-fold.21 The pharmacology of nicotine as studied in mammals is notably complex and unpredictable, partly because many sites of action are involved. Its effect on different human individuals is also diverse, but it has not been adequately investigated, particularly in view of the fairly well established fact that amblyopia and Buerger s disease occur in relatively rare cases directly because of its use.22... 

Salicylic acid 11.49 is another signaling molecule in the plant s response. The amount of jasmonic acid rises in 5 min after the insect begins feeding on the tobacco plant. The acid reaches the roots in 2 h and a flush of nicotine reaches the leaves (up to 120 mg/g leaf) in 7 h. Both of these acids can trigger the release of volatile compounds from the plant. These include not only terpenes, but also methyl jasmonate and methyl salicylate, which can signal nearby plants to mount their defenses against attack.183 Methyl jasmonate also inhibits the sprouting of potatoes.184... 

Nicotine, C10H14N2, is a highly toxic, pale yellow alkaloid produced in tobacco plants in response to leaf damage. Nicotine is synthesized in the roots of tobacco plants in response to hormones released by damaged tissue, and it is then carried to the leaves, where it is stored in concentrations of between 2 percent and 8 percent by weight. Nicotine is used commercially as an insecticide (it is one of the few poisons to which insects have not become resistant). Tobacco smoke contains nicotine, believed to be the active (and addictive) ingredient. 

Walling, 2000), less is known about plant responses to sucking or piercing insects (Du et al, 1998 Williams HI et al, 2005) (see Section on Regulation of Plant Toxicants by Natural Activators ). A recent study of the interactions between different types of herbivorous insects and plant defence volatiles showed that tobacco, Nicotiana tabacum, releases terpenoids and nicotine after caterpillar regurgitate treatment. Colonisation by western flower thrips, Frankliniella occidentalis, was reduced on the regurgitate treated plants, possibly due to the production of nicotine (Delphia et al, 2007). 

Winz RA, Baldwin IT (2001) Molecular interactions between the specialist herbivore Manduca sexta (Lepidoptera, Sphingidae) and its natural host Nicotiana attenuata. IV. Insect-induced ethylene reduces jasmonate-induced nicotine accumulation by regulating putrescine V-methyltransferase transcripts. Plant Physiol 125 2189-2202 Woeste KE, Kieber JJ (2000) A strong loss-of-fimction mutation in RANI results in constitutive activation of the ethylene response pathway as well as a Rosette-Lethal phenotype. Plant Cell 12 443-455... 

---