Mitko Subchev

Attraction of male turnip moths Agrotis segetum (Lepidoptera: Noctuidae) to sex pheromone components and their mixtures at 11 sites in Europe, Asia, and Africa

Selected combinations of (Z)-5-decenyl, (Z)-7-dodecenyl, and (Z)-9-tetradecenyl acetates, the pheromone components of the turnip mothAgrotisSegetum were tested for field attractancy at six, two, and three sites in Europe, Asia, and Africa, respectively. At all of the sites in Eurasia and in northern Africa the ternary mixture of the acetates captured most males, while at the sites south of the Sahara in Africa, (Z)-5-decenyl acetate alone was responsible for attraction. Differences in male attraction among the populations studied confirm the existence of significant population variation in the pheromone ofA. segetum. Interpretation of the present results together with earlier studies suggests that this variation is more or less continuous in Eurasia and north Africa, while a clearly distinct pheromone type is present in the areas south of the Sahara desert.

Pheromone variation among eastern European and a western Asian population of the turnip mothAgrotis segetum.

The female sex pheromone composition and the male electro-physiological response with respect to the three main sex pheromone components, (Z)-5-decenyl acetate, (Z)-7-dodecenyl acetate, and (Z)-9-tetradecenyl acetate, were investigated in populations ofAgrotis segetum from Armenia and Bulgaria. The percentage composition of the female-produced pheromone was 1∶52∶47 and 1∶42∶57 for the respective populations. Corresponding male receptor frequencies were 9∶90∶1 and 6∶92∶2. EAG response profiles of the male antennae were similar for the two populations. The populations from Armenia and Bulgaria differed from the earlier investigated French and Swedish populations, which have larger amounts of (Z)-5-decenyl acetate in gland extracts and have a majority of (Z)-5-decenyl acetate-sensitive receptors. Investigation of receptor frequencies on antennae of male Hungarian moths showed that individuals could be classified as either Swedish or Armenian/Bulgarian type. Males of the Swedish type were preferentially attracted to the three-component pheromone blend, whereas blends of (Z)-7-dodecenyl and (Z)-9-tetradecenyl acetate, and (Z)-7-dodecenol [pure or in mixture with (Z)-5-decenol] attracted the Armenian/Bulgarian type. The nature of pheromone variation among European and Asian populations of the turnip moth and possible mechanisms maintaining the variation are discussed.

Morphology of antennal sensilla auricillica and their detection of plant volatiles in the Herald moth, Scoliopteryx libatrix L. (Lepidoptera: Noctuidae).

In the Herald moth Scoliopteryx libatrix there are single superficial auricillic sensilla, as well as groups of s. auricillica located in cavities on the antennae. Two sensory neurones, with different dendrite diameters innervate each of these sensilla. The diameter of the smaller dendritic segment is roughly half that of the larger one. The larger dendritic outer segment branches profusely in the lumen of the sensillum, whereas the smaller dendrite has few branches. Electrophysiological recordings from s. auricillica located in the medial part of the cavity revealed a receptor neurone responding to Delta-3-carene. In addition to these neurones, recordings made deeper and more laterally into the cavity showed neurones that responded to (+/-)-linalool, alpha-pinene and green leaf volatiles.

Identification of cuticular hydrocarbons and the alkene precursor to the pheromone in hemolymph of the female gypsy moth, Lymantria dispar.

Hydrocarbons were extracted from the surface of the cuticle and from the hemolymph of adult female gypsy moths. GC and GC/MS analysis indicated that the cuticular hydrocarbons with chain lengths >21 carbons were the same as those found in the hemolymph. These consisted of mostly saturated straight chain hydrocarbons with heptacosane the major component. Methyl branched hydrocarbons were also identified including a series of tetramethylalkanes with chain lengths of 30, 32, and 34 carbons. In addition to those found on the cuticle surface, the hemolymph contained the alkene pheromone precursor, 2-methyl-Z7-octadecene and two saturated analogues, 2-methyl-octadecane and 2-methyl-hexadecane. No evidence was obtained for the presence of the pheromone 2-methyl-7, 8-epoxy-octadecane in the hemolymph. Pheromone gland extracts indicated that small amounts (<1 ng) of the alkene precursor were also present in the gland. Relatively larger amounts of the alkene precursor were found in the hemolymph at the time when pheromone titers were higher on the gland. The presence of the hydrocarbon pheromone precursor in the hemolymph is discussed in relation to possible biosynthetic pathways for producing the gypsy moth pheromone.

Sex pheromone biosynthetic pathway for disparlure in the gypsy moth, Lymantria dispar

The pheromone biosynthetic pathway for production of the sex pheromone disparlure, 2-methyl-7R,8S-epoxy-octadecane, was determined for the gypsy moth. Each step in the pathway was followed by using deuterium-labeled compounds that could be identified by using GC/MS. This approach provides unequivocal determination of specific reactions in the pathway. It was shown that the alkene precursor, 2-methyl-Z7-octadecene, is most likely made in oenocyte cells associated with abdominal epidermal cells. The pathway begins with valine contributing carbons for chain initiation, including the methyl-branched carbon, followed by chain elongation to 19 carbons. The double bond is introduced with an unusual Δ12 desaturase that utilizes a methyl-branched substrate. The resulting 18-methyl-Z12-nonadecenoate is decarboxylated to the hydrocarbon, 2-methyl-Z7-octadecene. The alkene is then transported to the pheromone gland through the hemolymph, most probably by lipophorin. At the pheromone gland, the alkene is unloaded and transformed into the epoxide disparlure for release into the environment. A chiral HPLC column was used to demonstrate that the (R,S)-stereoisomer of the epoxide, (+)-disparlure is found in pheromone glands.

Identification of Sex Pheromone Composition of Click Beetle Agriotes brevis Candeze

Geranyl butyrate (GB) and (E,E)-farnesyl butyrate (FB) were identified in the pheromone gland extract of females of the click beetle, Agriotes brevis (Candeze) (Coleoptera: Elateridae) as the major sex pheromone components. Polyethylene vial dispensers containing 20–200 mg of a 1:1 mixture caught high numbers of beetles. Captures did not decrease even after 73 days of field exposure of dispensers. At sites where both Agriotes sputator L. and A. brevis were present, the above baits were selectively catching only A. brevis, despite the fact that GB is also the main pheromone component of A. sputator, suggesting that FB has a role in reproductive isolation. In the early part of the season, traps into which the insects could both crawl and fly captured more A. brevis than designs where the insects could only fly in. Trap design was not important later in the season. This indicates the need for future development of a trap suitable for use throughout the whole season.

New Sex Attractant Composition for the Click Beetle Agriotes proximus: Similarity to the Pheromone of Agriotes lineatus

While testing traps baited with a blend of geranyl octanoate and geranyl butanoate (pheromone components previously identified for Agriotes lineatus, Coleoptera, Elateridae) in Portugal and Bulgaria, large numbers of the closely related Agriotes proximus were captured. In the literature, two different compounds, (E,E)-farnesyl acetate and neryl isovalerate had previously been identified as pheromone components of A. proximus. Subsequent field tests, conducted in several European countries, revealed that A. proximus was weakly attracted to geranyl butanoate on its own, while A. lineatus was weakly attracted to geranyl octanoate on its own. However, the largest catches for both species were observed with a blend of both compounds. No A. proximus was caught in traps baited with the blend of (E,E)-farnesyl acetate and neryl isovalerate at any of the test sites. In electroantennographic studies, antennae of male A. proximus and A. lineatus both gave greater responses to geranyl butanoate than to geranyl octanoate, suggesting that the perception of these two compounds was similar for both species. A 1:1 blend of geranyl octanoate and geranyl butanoate can be used as a bait in traps for the detection and monitoring of both A. lineatus and A. proximus in many European countries.

Major sex pheromone component of female Herald moth Scoliopteryx libatrix is the novel branched alkene (6Z, 13)-methylheneicosene

The major component of the female-produced sex pheromone of Scoliopteryx libatrix has been characterized by chemical analysis, synthesis, electrophysiological studies and field tests as (6Z,13)-methylheneicosene, probably the 13S-isomer. This is the first example of a branched chain alkene as a sex pheromone in the Noctuidae and is markedly different from the pheromones of other members of the family. The systematic position of S. libatrix, belonging to a monotypic genus of a one-member subfamily within the Noctuidae, may reflect the unusual structure of the sex pheromone.

Improving the floral attractant to lure Epicometis hirta Poda (Coleoptera: Scarabaeidae, Cetoniinae)

In order to improve the efficiency of the known floral attractant of Epicometis hirta [(E)-anethol and (E)-cinnamyl alcohol in a ratio of 1:1], candidate synergist compounds for field tests were selected through electroantennographic tests using the antennae of female and male E. hirta adult beetles. Among synthetic floral compounds 4-methoxyphenethyl alcohol and methyl salicylate evoked high responses from the antennae and were chosen for further field studies. In trapping tests in Bulgaria, the addition of 4-methoxyphenethyl alcohol to the E. hirta bait in the ratio of 1:1:1, in Hungary in ratios of 1:1:0.3 and 1:1:1 significantly increased catches. The addition of methyl salicylate was without effect in both countries. A high-capacity trap supplied with this ternary attractant could be more efficient for mass trapping purposes of E. hirta in environment-friendly plant protection.

Sex pheromone components of Mamestra suasa: chemical analysis, electrophysiological activity, wind tunnel activity and field tests in two European countries

(Z)‐11‐hexadecenyl acetate (Z‐11–16:Ac), (Z)‐11‐hexadecenal (Z‐11–16:Ald), (Z)‐11‐hexadecenol (Z‐11–16:OH) and hexadecanyl acetate (16:Ac) were found in pheromone gland extracts of female Mamestra suasa (Den. et Schiff.) in the relative amounts 100/2/10/5. All four compounds were also present in collections of airborne volatiles from calling females in a 100/7/5/5 ratio. No traces of 14 carbon aldehydes or acetates were detected. In gland extracts the presence of methyl hexadecanoate, methyl (Z)‐9‐hexadecenoate and methyl (Z)‐11‐hexadecenoate was demonstrated by base methanolysis. No methyl tetradecenoates were detected. In EAG tests Z‐11–16:Ac gave the best responses, followed by (Z)‐9‐tetradecenyl acetate (Z‐9–14:Ac), Z‐11–16:Ald and Z‐11–16:OH. In single sensillum recordings large spike amplitude cells in sensilla responded to Z‐11–16:Ac, while small spike amplitude cells to both Z‐11–16:OH and Z‐9–14:Ac. Cells responding to Z‐11–16:Ald were found in one out of 60 sensilla tested. In wind tunnel tests 0.1 μg of a 10:1 blend of Z‐11–16:Ac/Z‐11–16:Ald evoked the same responses and at a similar intensity as 3 isolated female pheromone glands did. In field tests a 10:1 blend of Z‐11–16:Ac/Z‐11–16:Ald caught significant numbers of males in both Bulgaria and Hungary. The addition of 16:Ac to the binary blend did not have any effect, while more than 1% of Z‐11–16:OH or 0.1170 of Z‐9–14:Ac dramatically decreased captures. In comparing different ratios of the acetate/aldehyde blend at different dose levels, best catches were recorded at the 10:1 ratio and at the highest (1000 μg) dose level.