Cuticular components

Cuticular diterpenes-duvanes and labdanes. Cutler have found that the cuticular diterpenes of green tobacco have both allelopathic and insect-deterrent effects (38). Present in the cuticle are duvane and/or labdane diterpenes (Figure 3) The levels of these specific cuticular components are believed to be responsible for the observed resistance of some types of tobacco to green peach aphids Myzus persicae (Sulzer), tobacco budworm Heliothis virescens (F.), and tobacco hornworm Manduca sexta (L.) (39). 

The //-alkanes usually range in chain length from 21 to 31 or 33 carbons. Hydrocarbons with fewer than 20 carbons commonly occur as pheromones, defensive compounds and intermediates to pheromones and defensive compounds, but their volatility makes them unsuited to function as cuticular components, n-Alkanes have been found on almost every insect species analyzed, and can range from less than one percent of the total hydrocarbons, as in tsetse flies (Nelson and Carlson, 1986 Nelson et al., 1988) to almost all of the hydrocarbon fraction, as in the adult tenebrionid beetle, Eurychora sp. (Lockey, 1985). Depending upon the species, they can consist of essentially only one major component, such as n-pentacosane in the American cockroach, Periplaneta americana (Jackson, 1972) to a series of //-alkanes, such as the series from C23 to C33 in the housefly, Musca domes-tica (Nelson et al., 1981), with trace amounts to C37 (Mpuru et al., 2001). In all cases, the odd-numbered alkanes predominate, due to their formation from mostly two carbon units followed by a decarboxylation (Blomquist, Chapter 3, this book). Small amounts of even-numbered carbon chain //-alkanes often occur, and presumably arise from chain initiation with a propionyl-CoA rather than an acetyl-CoA. Occasionally, gas chromatographic analyses reveal similar amounts of even-numbered chain //-alkanes and odd-numbered chain components. This is a red flag that the samples must be checked for contamination. 

Carlson, D.A. and Service, M. W. (1980). Identification of mosquitoes of Anopheles gambiae species complex A and B by analysis of cuticular components. Science,... 

First, almost all studies of insect cuticular lipids have used gas chromatography (GC) to analyze lipid extracts, using standard GC conditions that only allow compounds under C40 to be detected. More specialized GC equipment that can extend this range to >C60, in particular, columns that can withstand high temperatures (>400°C) are now available. However, they have not yet found routine use for cuticular lipid analysis, despite recent studies that have clearly demonstrated that cuticular lipids do indeed contain hydrocarbons, waxes, and other compounds with molecular weights above 500 daltons (Cvacka et ai, 2006). Thus, to date, many studies may only have examined subsets of the cuticular components. 

SEVERSON, R.F., ECKEL, R.V.W., JACKSON, D.M., SISSON, V.A., STEPHENSON, M.G., Aphicidal activity of cuticular components from Nicotiana tabacum, Nat. Engin. PestManag. Agents, 1994,551, 172-179. 

Propionate serves several unique and important roles in insects. It is used by some insects, in very small amounts, as a precursor to homomevalonate which is an intermediate in the biosynthesis of juvenile hormone (JH) II (1,2) and probably JH I and JH 0 as well. Much larger amounts of propionate and methylmalonate are needed for the biosynthesis of methyl branched hydrocarbons which are major cuticular components in most of the approximately 100 insect species whose cuticular lipids have been examined (3-7). Until recently, there was little information available on either the source of propionate or its metabolism in insects. In mammals vitamin B 2 Is a key cofactor in propionate and methylmalonate metabolism (B—9). Recent observations that some insect species lack or contain low levels of vitamin B 2 (10)... 

Figure 6 Sucrose ester mixtures isolated from the cuticular components of tobacco TI 165 (Refer to Table V for details).

Figure 7. Effects of sucrose ester mixtures isolated from the cuticular components of tobacco TI 16 5 on the growth of etiolated wheat (X aestivum L. cv Vakeland) coleoptiles. Significant inhibition (P<0.01) below solid line. Control broken line. (Refer to Figure 6 for details).

D. M. Jackson, G.R. Gwynn, J.F. Chaplin, and M.G. Stephenson Quantitation of major cuticular components from green leaf of different tobacco types J. Agr. Food Chem. 32 (1984) 566-570. 

Effects of Cuticular Components from Nicotiam Species... 

In this report, we will discuss investigations of the cuticular components from Nicotiana species and their effects on tobacco homworm and tobacco budworm moth oviposition. The response of tobacco budworm moths to specific cuticular isolates from a Nicotiana species also will be discussed. 

About six weeks after transplantation, cuticular components from field-grown plants of each Nicotiana species were extract by dipping young leaves in 8 oz. wide mouth bottles containing methylene chloride. After removal of the methylene chloride, the extract residue was treated with 1 1... 

Major cuticular components of species in section Repandae are hydroxacylnornicotines (24). 

TABLE V. Ovipositional Response of Tobacco Budworm Moths to Cuticular Components from Nicotiana spp. Applied to Nonpreferred TI 1112 (Entry A) in Paired Choice Tests with TI 1112 Sprayed with Solvent Blank (Entry B). 

Cuticular Components Applied to Entry A Amount Applied to Entry A (jtg/cr) Ovipositional Response When Compared With Solvent Blank... 

Knowledge of plant cuticular components which modify insect behavior will be useful in the control of a given pest. When the component is not a valuable quality factor for consumer acceptance, breeding of plants that lack ovipositional stimulants will reduce pest damage. The use of plant breeding to increase levels of insect ovipositional stimuli could produce plants which will be useful as trap crops. This could lead to the reduction in the use of pesticides which increases production costs and environmental contamination. 

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