Dudley I. Farman

Identification and Field Activity of a Male-Produced Aggregation Pheromone in the Pine Sawyer Beetle, Monochamus galloprovincialis

The pine sawyer beetle, Monochamus galloprovincialis, is a pest of pine trees in Europe and North Africa. Previously considered a secondary pest of stressed and dying trees, it is now receiving considerable attention as a vector of the pine wood nematode, Bursaphelenchus xylophilus, the causal agent of a lethal wilting disease in susceptible species of pines. Adult beetles are attracted to traps baited with a kairomone blend consisting of a host volatile, α-pinene, and two bark beetle pheromone components, ipsenol and 2-methyl-3-buten-2-ol. More recently it has been shown that mature male M. galloprovincialis produce a pheromone that attracts mature females in a laboratory bioassay. Here, volatiles were collected from mature male and female M. galloprovincialis, and a compound produced specifically by mature males was identified as 2-undecyloxy-1-ethanol from its gas chromatographic retention times, its mass spectrum, and by comparison with synthetic standards. The naturally-derived and synthetic compounds elicited electroantennographic responses from both females and males. Sealed polyethylene vials and polyethylene sachets were shown to be effective dispensers with zero-order release, the latter giving a higher release rate than the former. In two field tests, multiple-funnel traps baited with synthetic 2-undecyloxy-1-ethanol caught both female and male M. galloprovincialis, with higher catches at the higher release rate. This compound also synergized the attractiveness of the kairomone blend, the combined mixture catching 80–140% more beetles than the sum of the catches to each bait separately and luring up to two beetles/trap/d in a moderate-density population. We conclude that 2-undecyloxy-1-ethanol is a male-produced aggregation pheromone of M. galloprovincialis. This is the first example of a sex-specific compound in the cerambycid subfamily Lamiinae with significant behavioral activity in the field at a range sufficient to make it a useful trap bait. The possible roles of this pheromone in the chemical ecology of M. galloprovincialis and its potential use in pine wilt disease management are discussed.

Chemical basis for resistance in sweetpotato Ipomoea batatas to the sweetpotato weevil Cylas puncticollis

The aim of this work was to determine the basis of resistance in a sub-Saharan sweetpotato variety, New Kawogo, to the African sweetpotato weevil Cylas puncticollis. This insect feeds on the roots, reducing quality and yield, and is the most important production constraint of sweetpotato in Africa. Laboratory bioassays were designed to determine how the performance of weevils differed on susceptible and resistant roots. Subsequently, liquid chromatography-mass spectrometry (LC-MS) analysis of the root surface and root latex identified quantitative and qualitative differences in the chemical profiles with higher levels of octadecyl and hexadecyl esters of hydroxycinnamic acids reported in the resistant variety. The compounds were synthesized to confirm their identity and incorporated into artificial diets for bioassays on C. puncticollis. High levels of mortality and developmental inhibition were recorded for larvae feeding on treated diets, and the effect was dose-dependent. Thus, in contrast to previous work on resistant African sweetpotato cultivars, resistance in New Kawogo is not only active, but is quantifiable and manageable for breeding. Work is underway to determine what effect these compounds have on the weevils at a molecular level. The inheritance of the root latex esters will be studied in new crosses and mapped in new populations using quantitative trait loci (QTLs) that are currently being developed.

Volatile constituents of the essential oil of Cymbopogon citratus Stapf grown in Zambia

The hydrodistilled essential oil from the leaves of Cymbopogon citratus Stapf grown in Zambia was analysed by GC and GC–MS. Sixteen compounds representing 93.4% of the oil were identified of which geranial (39.0%), neral (29.4%) and myrcene (18.0%) were the major components. Small amounts of geraniol (1.7%) and linalol (1.3%) were also detected.

Minor Components in the Sex Pheromone of Legume Podborer: Maruca vitrata Development of an Attractive Blend

The legume podborer, Maruca vitrata (syn. M. testulalis) (F.) (Lepidoptera: Pyralidae) is a pantropical pest of legume crops. Sex pheromone was collected by gland extraction or trapping of volatiles from virgin female moths originating in India, West Africa, or Taiwan. Analysis by GC-EAG and GC-MS confirmed previously published findings that (E,E)-10,12- hexadecadienal is the most abundant EAG-active component with 2–5% of (E,E)-10,12-hexadecadienol also present. At least one other EAG response was detected at retention times typical of monounsaturated hexadecenals or tetradecenyl acetates, but neither could be detected by GC-MS. Laboratory wind-tunnel bioassays and a field bioassay of blends of (E,E)-10,12-hexadecadienal with (E,E)-10,12-hexadecadienol and a range of monounsaturated hexadecenal and tetradecenyl acetate isomers indicated greatest attraction of males was to those including (E,E)-10,12-hexadecadienol and (E)-10-hexadecenal as minor components. In subsequent trapping experiments in cowpea fields in Benin, traps baited with a three-component blend of (E,E)-10,12-hexadecadienal and these two minor components in a 100:5:5 ratio caught significantly more males than traps baited with the major component alone, either two-component blend, or virgin female moths. Further blend optimization experiments did not produce a more attractive blend. No significant differences in catches were found between traps baited with polyethylene vials or rubber septa, or between lures containing 0.01 and 0.1 mg of synthetic pheromone. Significant numbers of female M. vitrata moths, up to 50% of total catches, were trapped with synthetic blends but not with virgin females. At present there is no clear explanation for this almost unprecedented finding, but the phenomenon may improve the predictive power of traps for population monitoring.

Developing pheromone traps and lures for Maruca vitrata in Benin, West Africa

In previous work successful trapping of the legume podborer, Maruca vitrata Fabricius (Lepidoptera: Pyralidae), was accomplished using a synthetic pheromone blend consisting of (E,E)‐10,12‐hexadecadienal, (E,E)‐10,12‐hexadecadienol, and (E)‐10‐hexadecenal in a 100 : 5 : 5 ratio. In the present work, experiments were conducted in cowpea fields in Benin to compare different trap designs, and other aspects of the lures. A water‐trap made from a plastic jerry‐can was found to be superior to commercial funnel‐ and sticky‐trap designs, and 120 cm was the optimum height for captures. Generally, lures consisted of polyethylene vials containing 0.1 mg of pheromone. Results showed that shielding the lures from the adverse effects of sunlight with aluminium foil did not increase trap catches of M. vitrata. The degree of isomeric purity of the (E,E)‐10,12‐hexadecadienal and (E,E)‐10,12‐hexadecadienol blend components, in the range 73–99%, had no significant effect on captures, while lures of 80% isomeric purity showed no loss of effectiveness for up to 4 weeks. Similar results were observed with lures from a commercial source containing 0.46 mg of pheromone in the blend ratio 100 : 11 : 6 and 95% isomeric purity. Residue analysis showed that vial lures exposed for 2 weeks in the field still contained 73% of the initial amount of (E,E)‐10,12‐hexadecadienal, compared to rubber septa dispensers, which only retained 22%. Females comprised 11–50% of total catches, confirming earlier, unexpected results for synthetic lures. The observations that effective traps can be made from locally available plastic containers, and that pheromone blend composition and purity are not critical, should reduce costs and improve the feasibility of traps as practical monitoring tools for M. vitrata.

Female sex pheromone of brinjal fruit and shoot borer, Leucinodes orbonalis blend optimization.

The brinjal fruit and shoot borer, Leucinodes orbonalis is the major pest of eggplant in South Asia. Analysis of female pheromone gland extracts prepared from insects of Indian and Taiwanese origin confirmed (E)-11-hexadecenyl acetate (E11-16:Ac) as the major pheromone component with 0.8 to 2.8% of the related (E)-11-hexadecen-1-ol (E11-16:OH), as previously reported from Sri Lanka. The average quantity of E11-16:Ac extracted per female was estimated to be 33 ng, with a range of 18.9 to 46.4 ng when collected 2 to 3 hr into the scotophase. In field trials conducted in India, blends containing between 1 and 10% E11-16:OH caught more male L. orbonalis than E11-16:Ac alone. At the 1000 μg dose, on white rubber septa, addition of 1% E11-16:OH to E11-16:Ac was found to be more attractive to male L. orbonalis than either 0.1 or 10% E11-16:OH. Trap catch was found to be positively correlated with pheromone release rate, with the highest dose tested, 3000 μg, on white rubber septa catching more male moths than lower doses. Field and wind tunnel release rate studies confirmed that E11-16:OH released from white rubber septa and polyethylene vials at approximately twice the rate of E11-16:Ac and that the release rate of both compounds was doubled in polyethylene vials compared to white rubber septa. This difference in release rate was reflected in field trials conducted in Bangladesh where polyethylene vial dispensers caught more male moths than either black or white rubber septa, each loaded with the same 100 : 1 blend of E11-16:Ac and E11-16:OH in a 3000 μg loading.

Phenotypic Plasticity of Rhyzopertha dominica Pheromone Signaling: The Effects of Different Hosts and Presence of Conspecific Females on Male Produced Aggregation Pheromone

Male Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) release an aggregation pheromone consisting of a blend of two components, dominicalure 1 (D1) and Dominicalure 2 (D2). Pheromone from single insects, in different contexts, was collected and measured to determine if this signal is phenotypically plastic. Release rates were lowered when males were moved from maize grains to groundnut kernels or when moved from solitary occupation of maize grain to grain occupied by seven females. The pheromone release was increased again once these moves were reversed. The release of D1 was more affected than D2: thus, on groundnuts or in the presence of females, less pheromone was released and the proportion of D1 in the blend was lowered. Possible reasons for the modifications of the signal are discussed.

Resistance to the weevils Cylas puncticollis and Cylas brunneus conferred by sweetpotato root surface compounds.

Seven resistant varieties of sweetpotato were compared with three susceptible varieties in field trials and laboratory bioassays and showed that resistance was an active process rather than an escape mechanism, as field resistant varieties also had reduced root damage and oviposition compared with susceptible varieties in the laboratory. Liquid chromatography-mass spectrometry (LC-MS) of root surface and epidermal extracts showed significant variation in the concentration of hexadecyl, heptadecyl, octadecyl, and quinic acid esters of caffeic and coumaric acid, with higher concentrations correlated with resistance. All compounds were synthesized to enable their positive identification. Octadecyl coumarate and octadecyl caffeate applied to the surface of susceptible varieties in laboratory bioassays reduced feeding and oviposition, as observed on roots of resistant varieties, and therefore are implicated in weevil resistance. Segregating populations from breeding programs can use these compounds to identify trait loci for resistance and enable the development of resistant varieties.

Intermale Variation in Aggregation Pheromone Release in Prostephanus truncatus

Intermale variation in pheromone signaling has been confirmed and quantified by measurements of pheromone produced by single adult male Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae). Males varied in both the amounts of the two components of their aggregation pheromone and the ratio of one component to the other. The mean rates of production of the pheromone components T1 and T2 were 1.9 and 0.5 μg/day, respectively. There were repeatable differences among males in the amounts of T2 produced and the proportion of T1 in the pheromone blend over two weeks. Of the 15 males studied, one released a large burst of pheromone in a short period, while the remainder, if they did release, did so over an extended period. This suggested that there may be two alternative release strategies and the significance of this is discussed.

Chemical composition of the essential oil of Tagetes minuta L. from Zambia

Abstract The hydrodistilled oil of Tagetes minuta L. was analyzed by GC and GC/MS. The main components in the oil were dihydrotagetone (30.0%), (Z)-β-ocimene (23.6%), (Z)-tagetone (14.1%), limonene (8.3%) and (E)-tagetone (6.3%).