Alan Cork

Sex pheromones and their impact on pest management.

The idea of using species-specific behavior-modifying chemicals for the management of noxious insects in agriculture, horticulture, forestry, stored products, and for insect vectors of diseases has been a driving ambition through five decades of pheromone research. Hundreds of pheromones and other semiochemicals have been discovered that are used to monitor the presence and abundance of insects and to protect plants and animals against insects. The estimated annual production of lures for monitoring and mass trapping is on the order of tens of millions, covering at least 10 million hectares. Insect populations are controlled by air permeation and attract-and-kill techniques on at least 1 million hectares. Here, we review the most important and widespread practical applications. Pheromones are increasingly efficient at low population densities, they do not adversely affect natural enemies, and they can, therefore, bring about a long-term reduction in insect populations that cannot be accomplished with conventional insecticides. A changing climate with higher growing season temperatures and altered rainfall patterns makes control of native and invasive insects an increasingly urgent challenge. Intensified insecticide use will not provide a solution, but pheromones and other semiochemicals instead can be implemented for sustainable area-wide management and will thus improve food security for a growing population. Given the scale of the challenges we face to mitigate the impacts of climate change, the time is right to intensify goal-oriented interdisciplinary research on semiochemicals, involving chemists, entomologists, and plant protection experts, in order to provide the urgently needed, and cost-effective technical solutions for sustainable insect management worldwide.

1-Octen-3-ol. A potent olfactory stimulant and attractant for tsetse isolated from cattle odours

Recording of electroantennographic (EAG) responses from tsetse, Glossina pallidipes and G. morsitans morsitans (Diptera: Glossinidae) has been used to detect olfactory stimulants in volatiles from cattle. The most potent stimulant in cattle odours collected on Porapak resin has been identifiedas 1-octen-3-ol by gas chromatographic retention data and mass spectrometry. The rate of production of 1-octen-3-ol by a normal ox was estimated to be 0.043 mghr−1, and the natural material was shown to be predominantly the (R)-(−)enantiomer. No 1-octen-3-ol was collected under the conditions used in the absence of an ox. EAG dose-response curves to 1-octen-3-ol showed it to be about 106 times more potent than acetone, a known attractant for tsetse, with the maximum response of about 1 mV occurring to approx. 1 ng at source. 1-octen-3-ol caused increased upwind flight by tsetse in a wind tunnel bioassay, and in the field it was attractive to tsetse by itself and also increased the attractiveness of both ox odour and of mixtures ofcarbon dioxide and acetone.RésuméLes réponses électroantennographique (EAG) des mouches tsé-tsé, Glossina pallidipes et G. morsitans morsitans (Diptera: Glossinidae), ont été notées afin de découvrir les stimulants olfactifs parmi les composés volatils émanant du bétail. Le stimulant le plus puissant dans l’odeur de bétail, recueillié sur la résine Porapak, a été identifié comme 1-octen-3-ol en utilisant des données de rétention chromatographique en phase gazeuse et spectrométrie de mass. On a estimé le taux de production de 1-octen-3-ol par un boeuf normal à 0,043 mg hr−1 et la matiére naturelle s’est révélée comme composée en majeure partie de l’enantiomère (R)-(−). Dans les conditions utilisées, on n’a recueillié de 1-octen-3-olqu’enpresence d’un boeuf. Les courbes de dosage-réponse EAG pour 1-octen-3-ol l’a révélé à peu près 106 fois plus puissant que l’acétone, un attractant connu pour les mouches tsé-tsé, la réponse maximum d’environ 1 mV étant enregistrée pour environ 1 ng à la source. 1-octen-3-ol a occasionne un accroissement de vol des mouches tsé-tsé contre le vent dans un tunnel aérodynamique. Sur le terrain 1-octen-3-ol s’est révélé attractif tout seul et a augmenté la puissance attractive de l’odeur de boeuf et aussi dés mélanges de bioxyde de carbone et d’acétone.

Electrophysiological and Behavioral Responses of Female Helicoverpa armigera to Compounds Identified in Flowers of African Marigold, Tagetes erecta

Seven electrophysiologically active compounds were detected in air-entrained headspace samples of live flowers of Tagetes erectaanalyzed by gas chromatography (GC) linked to a female Helicoverpa armigeraelectroantennograph (EAG) using polar and nonpolar capillary columns. These compounds were subsequently identified using GC linked to mass spectrometry as benzaldehyde, (S)-(−)-limonene, (R,S)-(±)-linalool, (E)-myroxide, (Z)-β-ocimene, phenylacetaldehyde, and (R)-(−)-piperitone. Electrophysiological activity was confirmed by EAG with a 1-μg dose of each compound on filter paper eliciting EAG responses that were significantly greater than the solvent control response from female moths. Wind-tunnel bioassays with T. erectaheadspace samples, equivalent to 0.4 flower/hr emission from a live flower, elicited a significant increase in the number of upwind approaches from female H. armigerarelative to a solvent control. Similarly, a seven-component synthetic blend of EAG-active compounds identified from T. erectapresented in the same ratio (1.0 : 1.6 : 0.7 : 1.4 : 0.4 : 5.0 : 2.7, respectively) and concentration (7.2 μg) as found in the natural sample elicited a significant increase in the number of upwind approaches relative to a solvent control during a 12-min bioassay that was equivalent to that elicited by the natural T. erectafloral volatiles.

Landing responses of Anopheles gambiae elicited by oxocarboxylic acids

Abstract A wind tunnel bioassay and video system were used to observe Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) landing on glass cylinders, heated to human skin temperature (34°C) and treated with aqueous solutions of oxocarboxylic acids. Six of nine compounds tested: 2‐oxobutanoic, 2‐oxo‐3‐methylbutanoic, 2‐oxopentanoic, 2‐oxo‐3‐methylpentanoic, 2‐oxo‐4‐methylpentanoic and 2‐oxohexanoic elicited significant landing responses in comparison to a water control. Landing responses appeared to be restricted to C4–C6, 2‐oxocarboxylic acids. A solution of 1 µg/µL of 2‐oxopentanoic acid elicited the highest level of response that was temperature dependent: significant numbers of landings occurred only within ± 2°C of human skin temperature. Chemical analysis by linked gas‐liquid chromatography/mass spectrometry of methyl‐oxime, trimethylsilyl derivatized samples of human sweat extracts revealed the presence of 2‐oxopropanoic (pyruvic) acid and three behaviourally active, branched chain acids: 2‐oxo‐3‐methylbutanoic, 2‐oxo‐3‐methylpentanoic and 2‐oxo‐4‐methylpentanoic.

Identification of major component of male-produced aggregation pheromone of larger grain borer, Prostephanus truncatus (horn) (coleoptera : bostrichidae)

Male beetles of the larger grain borer,Prostephanus truncatus Horn (Coleoptera: Bostrichidae) were shown to produce material causing an electroantennographic (EAG) response from both male and female beetles. Volatiles from mixed sex cultures were collected on Porapak Q and fractionated by liquid chromatography (LC) with gradient elution. The total volatiles and the fractions were analyzed by gas chromatography (GC) linked to EAG, and two compounds eluting in the same LC fraction elicited EAG responses from male and female beetles. These were assumed to be components of the male-produced aggregation pheromone. Amounts of these compounds obtained were very low and less than 10−3 times the amounts of the aggregation pheromone components produced by the related species,Rhyzopertha dominica, under similar conditions. The most abundant of these EAG-active compounds was identified as 1-methyiethyl (2E)-2-methyl-2-pentenoate by comparison of its GC retention times and mass spectrum with those of synthetic analogs. The synthetic compound elicited electrophysiological and behavioral responses in both male and female beetles significantly greater than those to structural analogs. This compound is attractive toP. truncatus beetles in the field, and has been given the trivial name of “trunc-call 1”.

Identification of electrophysiologically‐active compounds for New World screwworm, Cochliomyia hominivorax, in larval wound fluid

Abstract Acidic and non‐acidic fractions from extracts of fluid from sheep wounds infested with larvae of Cochliomyia hominivorax (Coquerel) were analysed by linked gas chromatography and electroantennography in order to detect electrophysiologically‐active compounds that could be potential attractants. Responses to twenty‐six electrophysiologically‐active compounds were observed and, on the basis of electron impact and chemical ionization mass spectrometry and co‐chromatography with authentic compounds, twenty‐five of these compounds were characterized. The most abundant compounds identified in the larval wound fluid were straight and methyl‐branched aliphatic carboxylic acids, ranging from C2‐ to C5‐carbon chain length. Butanoic acid, for example, was found to be present at approximately 0.45mg/ml. Aliphatic carboxylic acids with longer chain lengths were also observed but in trace amounts. Three aromatic carboxylic acids, benzoic, phenylethanoic and 3‐phenylpropanoic acids were also present but only phenylethanoic and 3‐phenylpropanoic acids elicited electroantennographic responses. Phenol and indole were by far the most abundant components of the non‐acid fraction of the larval wound fluid with all other components, except δ‐valerolactam, present at levels of less than 5% that of phenol which was present at a concentration of 0.05 mg/ml.

Attractant Volatiles Released by Female and Male Triatoma infestans (Hemiptera: Reduviidae), a Vector of Chagas disease: Chemical Analysis and Behavioral Bioassay

Abstract Volatiles emitted by male and female T. infestans before and during copula were collected on Porapak-Q filters, desorbed with dichloromethane, and analyzed by gas chromotography and gas chromatography-mass spectrometry after confirmation of attractiveness in an arena bioassay. Chemical analysis confirmed the presence of (R,S)-2- and 3-methylbutan-1-ol in a 2:1 ratio; short chain acids (ethanoic to nonanoic acid); long chain acids decanoic to (Z)-9-octadecenoic acid; aliphatic aldehydes (hexanal to nonanal), benzaldehyde and dipropylsulphide from insects in copula. Electroantennographic studies conducted with a homologous series of aliphatic aldehydes on female and male T. infestans showed that, for a given dose, EAG responses elicited from both sexes increased with increased chain length up to nonanal, after which EAG-activity declined. Attractiveness of non-acidic trace components identified in the volatiles were tested on male and female T. infestans, in an arena bioassay using a video tracking method. Aliphatic C6 to C10 aldehydes were tested: hexanal (1–100 μg) and heptanal (10 μg) were attractive to female T. infestans, high doses of octanal and nonanal (1–100 μg) were unattractive to male and female T. infestans but low doses of nonanal (0.01–0.1 μg) were attractive to male T. infestans. Benzaldehyde was highly attractive to female T. infestans at low doses (0.05–0.1 μg). 3-methylbutan-1-ol was attractive to male T. infestans at high dose (1,000 μg). (S) or (S,R) 2-methyl-butan-1-ol were anattractive to males or females (1–1,000 μg). Blends of hexanal and benzaldehyde (20:1 and 40:1) showed an additive effect on attraction compared with hexanal alone, when tested on female T. infestans. The study has demonstrated the presence of a number of electrophysiologically and behaviorally active compounds in volatiles emitted by T. infestans in copula that may have a role in the postulated copulation pheromone.

Sex pheromone production in Callosobruchus maculatus (Coleoptera: Bruchidae): electroantennographic and behavioral responses.

Behavioral and electroantennogram (EAG) assays were used to determine rhythmicity and dynamics of the sex pheromone biology of the bruchid beetle, Callosobruchus maculatus (F.). Beetles were sexually active throughout the photophase. Virgin females entrained to a 16:8 L:D light cycle emitted more sex pheromone during the first half of photophase than during the second half of photophase or during scotophase. Sex pheromone production increased from day 0 to day 3 of adult life, and then decreased as females grew older. Availability of garbonzo beans, one of the larval food and adult oviposition hosts, to females did not stimulate sex pheromone production. Mating resulted in a reduction in post-coital sex pheromone production. Mated females, however, regained attractiveness to males and this attractiveness increased from day 1 to day 3 after first mating when females had been mated at day 0 after emergence. (Z)-3-Methyl-2-heptenoic acid (Z32A) and (Z)-3-methyl-3-heptenoic acid (Z33A), two compounds implicated as sex pheromone components for C. maculatus, both elicited male EAG and behavioral responses in the beetles; however, Z33A elicited larger responses than Z32A. Binary mixtures of the two compounds were more effective than either compound alone.

Components of female sex pheromone of cocoa pod borer moth,Conopomorpha cramerella

The cocoa pod borer,Conopomorpha cramerella (Snellen) (Lepidoptera: Gracillariidae), is the most serious pest of cocoa in Southeast Asia. Analyses of ovipositor washings and entrained volatiles from virgin female moths by gas chromatography (GC) linked to electroantennography (EAG), and comparison of EAG responses from the male moth to synthetic compounds indicated the presence of theE,Z,Z andE,E,Z isomers of 4,6,10-hexadecatrienyl acetate and the corresponding alcohols, and of hexadecyl alcohol. Amounts of pheromone produced were less than 0.1 ng/female, and no peaks for the unsaturated components were observed on GC analysis. Extensive field testing of synthetic mixtures in Sabah, East Malaysia, showed that traps baited with a polyethylene vial impregnated with 1.2 mg of a mixture of the above five components in 40∶60∶4∶6∶10 ratio caught more maleC. cramerella moths than traps baited with a virgin female moth.

SEX PHEROMONES OF RICE MOTH, Corcyra cephalonica STAINTON II. Identification and Role of Female Pheromone

Laboratory investigations of mating behavior in the rice moth,Corcyra cephalonica Stainton (Lepidoptera: Pyralidae; Galleriinae) showed that male moths are attracted at short range to live, virgin female moths and to female abdominal-tip extract. Volatiles collected from virgin female moths contained one component eliciting an electroantennographic (EAG) response from the male moth, and the chemical, spectroscopic, and Chromatographic data on this component were consistent with that of synthetic 6,10,14-tri-methyl-2-pentadecanol. This compound caused an EAG response from the male moth and attracted male moths in the bioassay. The pheromone is thought to play a role in courtship, and the synthetic material was shown to cause the male moths to search for a mate and attempt copulation.