Scarabs

Macrolide aggregation pheromones produced by male cucujid beetles are derived from fatty acids. Feeding experiments with labeled oleic, linoleic, and palmitic acids indicate incorporation into the macrolide pheromone component [ 117 ]. The biosynthesis of another group of beetle pheromones, the lactones, involves fatty acid biosynthetic pathways. Japonilure and buibuilactone biosynthesized by the female scarab, Anomalajaponica, involves A9 desaturation of 16 and 18 carbon fatty acids to produce Z9-16 CoA and Z9-18 CoA,hydroxylation at carbon 8 followed by two rounds of limited chain shortening and cyclization to the lactone [118]. The hydroxylation step appears to be stereospecific [118]. 

Although not of fatty acid origin another group of scarab beetles utilizes amino acid derivatives as pheromones [119]. The large black chafer, Holotrichia parallela, uses L-isoleucine methyl ester [ 120] and the cranberry white grub, Phyllophaga anxia, uses both L-isoleucine and i.-valine methyl esters [121]. More recently L-isoleucine methyl ester, N-formyl L-isoleucine methyl ester, and N-acetyl L-isoleucine methyl ester were identified in the scarab beetle Phyllophaga elenans [ 122]. These pheromone components are obviously derived from the amino acids isoleucine and valine. 

The amino acid 26, which has been isolated from various Amanita fungi [35], is one of the few examples of a natural product with an achiral allene moiety (Scheme 18.10) and was prepared inter alia by Strecker synthesis and also substitution reactions of allenic bromides and phosphates [36]. Recently, even unfunctionalized allenes have been found in nature seven allenic hydrocarbons 27 with chain lengths ranging from C23 to C31 were isolated from the skin of the Australian scarab beetle Anti-trogus consanguineus and related species (Scheme 18.10) [37]. Also these allenes do not occur in enantiomerically pure form, but with enantiomeric excesses of86-89% ec. 

Largely, the insect detectors for pheromones and other semiochemicals are arrays of hair-like sensilla distributed over the surface of the antennae and palps. In some species, such as scarab beetles [3, 4] and the honeybee [5], semiochemicals are received by olfactory plates. The more ubiquitous hair-like sensilla typically consist of hollow cuticular hairs (10-400 pm long, 1-5 pm thick) innervated by one or several olfactory receptor cells (neurons) and three auxiliary cells [6]. 

Scarabaeidae (Scarab Beetles, Chafers, Dung Beetles). 109... 

Pheromone chemistry in scarab beetles, chafers, and dung beetles covers a wide range of structures, including esters of amino acids and aromatics as well as branched and straight chain aliphatic compounds, among which a row of y-lactones forms a most characteristic group. 

The male released pheromone of Osmoderma eremita is (R)-5-hexyloxacy-clopentan-2-one 68 [139] (Scheme 7). In contrast, in other scarab species, pheromones are mostly produced by females. 

Females of several species use (R)-5-[(lZ)-l-octenyl]oxacyclopentan-2-one, buibuilactone 69 [ 140-144]. The first y-lactone identified from a scarab beetle was (R)-5-[(Z)-l-decenyl]oxacyclopentan-2-one, japonilure 70, the female produced sex pheromone of the Japanese beetle Popillia japonica [145]. Both 69 and 70 are components of specific blends of several species [140-143]. The Japanese beetle is extremely sensitive to the non-natural enantiomer of his pheromone as little as 1% of the (S)-enantiomer inhibits the attractiveness of the pheromone [ 145]. With respect to species discrimination, this is particularly... 

Two related scarab species produce ethyl 4-methyloctanoate 78 (Scheme 8) as an aggregation pheromone the African rhinoceros beetle Oryctes monoceros [170] and the coconut rhinoceros beetle Oryctes rhinoceros [171, 172]. The latter is readily attracted to the racemate. Its secretion was found to contain the free acid as well as ethyl 4-methylheptanoate [ 171 ]. Similarly to other cases, the attractiveness of ethyl 4-methyloctanoate is enhanced by host compounds, i.e. coconut wood [173]. The date palm fruit stalk borer, Oryctes elegans, uses 4-methyloctanoic acid as a male produced pheromone [174]. Structurally... 

Females of several other species of scarab beetles use methyl esters of L-iso-leucine 83 and l-valine 84 as sex pheromones [179,180]. In Phyllophaga elenans, apart from 83, the corresponding N-formyl- and AT-acetyl derivatives have been... 

Recently, two new facets have been added to scarab chemistry. A suite of unusual A9 10-allenic hydrocarbons like 86 has been identified among the cutic-ular hydrocarbons from several Australian melolonthine scarab beetles [184]. Though very low-level components in the related cane beetle Antitrogus parvu-luSy the major cuticular hydrocarbons in this species proved to be oligomethyl-docosanes like 87. Only the relative configurations of these compounds could be determined [185]. Whether these interesting hydrocarbons have a function as pheromones needs to be established. 

The female produced long range sex pheromone of Migdolus fryans is AT-[(2 S)-2-methylbutyl]-(2S)-2-methylbutyramide 185 [345]. The acyl part as well as the alkyl part may be derived from isoleucine. Interestingly, this amide is accompanied by the ethyl ester of N-formyl isoleucine, which is also known from the scarab beetle, Phyllophaga elenans [181]. This amino acid derivative proved to be not attractive for both species its biological significance remains to be clarified. 

Leal W (1999) Scarab beetles. In Hardie J, Minks AK (eds) Pheromones of non-lepi-dopteran insects associated with agricultural plants. CABI Publishing, Oxford, UK... 

The female-produced sex pheromone of the scarab beetle, Phyllophaga lanceolata was identified as the methyl ester of an essential amino acid, L-leucine. Three amino acid derivatives were identified in the extracts of pheromone glands of the scarab beetle, Phyllophaga elenans. These were... 

L-isoleucine methyl ester, N-formyl L-isoleucine methyl ester and N-acetyl L-isoleucine methyl ester. The major component of the male attractant pheromone of the scarab beetle, Holotrichia reynaudi, was identified as anisole. ... 

Extracts of the summer chafer, Amphimallon solstitiale L. (Coleoptera Scarabaeidae), a common European scarab beetle were analyzed by GC-MS and GC-EAD. Both male and female extracts were shown to contain Acetoin — R) (5) > 9 1, as well as 2,3-butanediol — 2R, 3R) (25,35) meso =1 1 9. Although (25, 35)-butanediol did not show any activity, the other compounds elicited strong responses exclusively with male antennae. 

Hansson, B. S., Larsson, M.D. and Leal, W. S. (1999). Green leaf volatile-detecting olfactory receptor neurones display very high sensitivity and specificity in a scarab beetle. Physiological Entomology 24 121-126. 

Symmetry establishes a ridiculous and wonderful oousinship between objects, phenomena, and theories outwardly unrelated terrestial magnetism, women s veils, polarized light, natural selection, the theory of groups, invariants and transformations, the work habits of bees in the hive, the structure of space, vase designs, quantum physics, scarabs, flower petals,... 

Tada S. and Leal W. S. (1997) Localization and morphology of the sex pheromone glands in scarab beetles (Coleoptera Rutelinae, Melolonthinae). J. Chem. Ecol. 23, 903-915. 

The female-produced sex pheromones of several different species of scarab beetles have been identified, and they include a wide variety of structures. Although many appear to be fatty acid-derived, isoprenoid- and amino acid-derived compounds are also represented (reviewed in Leal, 1998b, 1999). 

In contrast to the rutelines, the melolonthine scarabs generally use terpenoid-and amino acid-derived pheromones (reviewed in Leal, 1999). For example, the female large black chafer, Holotrichia parallela Motschulsky, produces methyl (2.S, 3. Sj - 2 - am ino-3-methy lpcn tanoatc (L-isoleucine methyl ester) as an amino acid-derived sex pheromone (Leal et al., 1992 Leal, 1997). There is no direct evidence that the chafer beetles or any other Coleoptera use the shikimic acid pathway for de novo pheromone biosynthesis, but some scarabs and scolytids (see section 6.6.4.2) may convert amino acids such as tyrosine, phenylalanine, or tryptophan to aromatic pheromone components (Leal, 1997,1999). In another melolonthine species, the female grass grab beetle, Costelytra zealandica (White), the phenol sex pheromone is produced by symbiotic bacteria (Henzell and Lowe, 1970 Hoyt et al. 1971). 

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