Teodora B. Toshova

Electrophysiological Responses of the Lepidopterous Stemborers Chilo partellus and Busseola fusca to Volatiles from Wild and Cultivated Host Plants

The stemborers Chilo partellus and Busseola fusca are major pests of subsistence cereal farming in Africa. Volatiles released by two cultivated hosts, sorghum and maize (Sorghum bicolor and Zea mays), and two wild grass hosts, Pennisetum purpureum and Hyparrhenia tamba, were collected by air entrainment. Electrophysiologically active components in these samples were detected by coupled gas chromatography-electroantennography (GC-EAG), and the active peaks identified by gas chromatography-mass spectrometry. A total of 41 compounds were identified from the four plant species, all of which, as well as two unidentified compounds, elicited an electrophysiological response from one or both of the stemborers. The compounds included a number of green leaf volatiles and other aliphatic aldehydes, ketones, and esters, mono- and sesquiterpenoids, and some aromatic compounds. EAG studies with authentic samples, conducted at two discriminating doses for all compounds, and dose–response curves for 14 of the most highly EAG-active compounds, showed significant differences in relative responses between species. The compounds that elicited large responses in both species of moths included linalool, acetophenone, and 4-allylanisole, while a number of compounds such as the aliphatic aldehydes octanal, nonanal, and decanal elicited a large response in B. fusca, but a significantly smaller response in C. partellus. Furthermore, the wild hosts produced higher levels of physiologically active compounds compared with either of the cultivated hosts. These differences are discussed in relation to the differential attraction/oviposition of the two stemborers observed in the field and, particularly for eastern African small-scale farming systems, in the context of using a push–pull strategy for their control.

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.

Catches of vine bud moth Theresimima ampellophaga (Lep., Zygaenidae: Procridinae) males in pheromone traps: Effect of the purity and age of baits, design, colour and height of the traps, and daily sexual activity of males

Pure (2R)‐butyl (7Z)‐tetradecenoate, as well as racemic 2‐butyl (7Z)‐tetradecenoate, in a dose of 100 μg (calculated for the active (2R)‐enantiomer) applied onto serum bottle caps of grey rubber, were an effective pheromone bait for Theresimima ampellophaga (Bayle‐Barelle, 1808) (Lepidoptera: Zygaenidae: Procridinae). This bait remained active for longer than one full flight of the pest in the regions with one generation per year. Colourless transparent as well as red and yellow sticky traps were the cheapest and most simple design for trapping T. ampellophaga, while green and blue traps performed worse. Among the traps tested, VARL (CSALOMON®) funnel traps had the highest capture ability for the pest. Traps had to be mounted at least 1.0–2.0 m above ground level. T. ampellophaga males flew to a source of sex pheromone all day long with a main peak between 07.00 and 09.00 hours and a much smaller one between 19.00 and 21.00 hours.

Agriotes proximus and A. lineatus (Coleoptera: Elateridae): a comparative study on the pheromone composition and cytochrome c oxidase subunit I gene sequence

The presence of geranyl octanoate, previously found in pheromone gland extracts of Agriotes lineatus females, was also demonstrated in gland extracts of A. proximus females. Similar to A. lineatus, geranyl butanoate was present only in trace amounts in A. proximus female gland extracts. In air entrainment samples of female A. lineatus and A. proximus beetles, the relative ratio of geranyl butanoate and geranyl octanoate was higher than that in gland extracts. In addition, comparison of a segment of the mitochondrial cytochrome c oxidase subunit I gene of feral specimens of A. lineatus and A. proximus showed >99% similarity. Both pheromone profile and nucleotide sequence analysis delineate close relationship between the investigated taxa and postulate taxonomic revision. Further studies on sympatric populations of A. lineatus and A. proximus are underway to investigate and better understand possible processes of species diversification.

The seasonal activity of flea beetles in Bulgaria

Using allyl-isothiocyanate-baited traps, we recorded six species of flea beetles in cabbage and horseradish crops in the region of Sofia, Bulgaria in 2006 and 2007. The most abundant species in the traps was Ph. cruciferae (92–96%) followed by Ph. vittula, Ph. undulata and Ph. nigripes. The overwintering adults of these species emerge before the beginning of April and are active to the end of May–beginning of June. Catches of adults of the new generation occurred from the end of June–beginning of July to the second half of October–beginning of November. In 2006, air temperature and humidity strongly influenced the catches of the flea beetles. Investigations of the reproductive status of field collected females of Ph. cruciferae showed that this species develops one generation per year in the region. The results of this study can be used in integrated pest management approach to flea beetles control.

Electrophysiological responses and field attraction of the grey corn weevil, Tanymecus (Episomecus) dilaticollis Gyllenhal (Coleoptera: Curculionidae) to synthetic plant volatiles

The grey corn weevil, Tanymecus (Episomecus) dilaticollis, is an economically important polyphagous pest in Eastern and Central Europe. The present research is the first published electrophysiological study of olfactory sensitivity of adult T. dilaticollis to plant volatiles. The electrophysiological responses of male and female antennae were recorded to 20 synthetic volatile organic compounds (VOCs), previously identified to be released from the preferred host plants, maize and sunflower. Antennae of both sexes responded to a wide range of volatiles from different chemical classes: fatty acid derivatives, aromatic compounds and terpenoids. Two green leaf volatiles, (E)-2-hexen-1-ol and (Z)-3-hexen-1-ol, and one terpenoid, (±)-linalool, elicited the strongest electrophysiological responses by male and female antennae. Relatively high electrophysiological activity by T. dilaticollis antennae was also recorded to benzaldehyde, eugenol and caryophyllene. In the field, (E)-2-hexen-1-ol and (Z)-3-hexen-1-ol, when presented individually, caught significantly more male and female T. dilaticollis than unbaited controls. These compounds could be developed into an attractive trap for the detection and monitoring of T. dilaticollis.

Illiberis (Primilliberis) rotundata Jordan (Lepidoptera: Zygaenidae: Procridinae) male sex attractant: Optimization and use for seasonal monitoring

Illiberis (Primilliberis) rotundata Jordan, 1907 (Lepidoptera: Zygaenidae) is an orchard pest distributed in Honshu, Shikoku and Kyushu in Japan and also in China, Korea, Mongolia and Russia (south‐eastern Siberia and Far East). For optimizing a known sex attractant lure containing sex pheromone components of the species (2R)‐butyl (7Z)‐dodecenoate and (2R)‐butyl (9Z)‐tetradecenoate, field work was organized in three cherry tree plots in Naruto, Tokushima in 2009 and 2010. As a result, the mixture of (2R)‐butyl (7Z)‐dodecenoate and (2R)‐butyl (9Z)‐tetradecenoate in a ratio of 30:100–50:100 (130–150 µg, respectively) was found to be the most attractive for the males of this pest. The seasonal flight of I. rotundata in Naruto, Japan as estimated by pheromone traps started at the end of May and lasted up to the end of June with a mass flight at the very end of May to first week of June.

Sitona Weevils (Coleoptera: Curculionidae) Caught by Traps in Alfalfa Fields in Bulgaria

ABSTRACT Modified sticky Delta traps and PAL CSALOMON® traps, unbaited or baited with synthetic aggregation pheromone of Sitona lineatus (L., 1758), 4-methyl-3,5-heptanedione, were used for studying the species spectrum of Sitona (Coleoptera: Curculionidae) weevils in alfalfa fields in the regions of Sofia, Plovdiv and Pazardzhik in 2007 and 2008. Several Sitona species, all known as pests on leguminous crops in Bulgaria, were caught. Modified sticky Delta traps baited with 4-methyl- 3,5-heptanedione caught significantly higher number of Sitona weevils than the unbaited traps.