Electroantennogram responses of the Mediterranean fruit fly, Ceratitis capitata to identified volatile constituents from calling males

Fifty-six compounds from the odor of calling, sexually mature, laboratory reared males of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) were isolated by headspace trapping on Tenax columns and identified using GC/MS techniques (69 total compounds were detected). Electroantennogram responses (EAGs) to 54 of the 56 identified compounds as well as 5 analogs were tested on both sexes. Significant differences between the sexes in their responsiveness were found in 9 of the 54 identified compounds tested. There was no correlation between the amplitude of the EAG response and the relative abundance of compound identified from headspace analysis. Of the five major identified components, three elicited relatively small EAG responses, while two elicited large EAGs compared to the hexan-1-ol standard. The relative ranking of EAG responses were: methyl and ethyl hexenoates and hexanoates > C₄–C₆ esters and/or acetates > ethyl and methyl octenoates > monoterpenes > sesquiterpenes > C₂–C₅ acetates, alcohols and ketones. Behavioral bioassays on each of the five major identified components as well as a blend of six of the compounds showed some degree of attractancy to virgin females which in some cases approached the response to a pheromonal standard (male odors absorbed onto filter paper). These results are discussed in relationship to the insect's antennal sensitivity to putative pheromone components and/or allomonal components and to other reported C. capitata pheromone studies.

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Résumé Cinquante-six composés de l'odeur de mâles de C. capitata Weidemann, élevés en laboratoire, sexuellement mûrs et en appel, ont été isolés par piégeage sur colonnes tenax et identifiés par la technique GC/MS (69 composés avaient été détectés en tout). Les électroantennogrammes (EAGs) ont été examinés chez les deux sexes pour 54 des 56 composés identifiés et 5 de leurs analogues. Des différences significatives entre les sexes ont été observées pour 9 des 54 composés identifiés. Il n'y avait pas de corrélation entre l'ampleur de l'EAG et l'abondance relative du composé lors de son isolement. Pour les 5 principaux composés identifiés, 3 ont induit des EAGs relativement faibles, tandis que 2 étaient importants, par comparaison avec l'Hexane-1-ol utilisé comme témoin. Le classement relatif des EAG a été: hexénoates et hexanoates d'éthyl et de méthyl C₄–C₆ esters et/ou acétates octénoates d'éthyl ou de méthyl monoterpènes sesquiterpènes C₂–C₅ acétates, alcools et kétones. Les expériences de comportement avec chacun des 5 composés principaux identifiés, comme avec des mélanges de 6 composés ont mis en évidence une attraction des femelles vierges qui dans quelques cas avoisine la réponse à la phéromone témoin (odeur du mâle absorbée sur papier filtre). Ces résultats sont discutés en fonction de la sensibilité de l'antenne d'insexte aux composés supposés de la phéromone et aux composés allomonaux, et en fonction des autres études connues sur les phéromones de C. capitata.

     

Stamens are not essential as an attractant for pollinators in females of cryptically dioecious Thalictrum pubescens Pursch. (Ranunculaceae)

 It has been hypothesized that females of some dioecious species maintain stamens that produce sterile pollen as a means of attracting pollinators to promote greater seed set. However, this hypothesis has rarely been tested. This paper examines the role of pollinators in the maintenance of sterile stamens in the cryptically dioecious species, Thalictrum pubescens. Wind was found to contribute to pollination; branches of female T. pubescens enclosed in cheesecloth to exclude insects but not wind were still able to set seed. Therefore, females may not need the stamens for pollination. In 1994, insects were found to discriminate against emasculated female flowers, but this discrimination did not lead to a significant difference in either the amount of pollen received or seed set. In 1995, emasculation was combined with the addition of pollen to determine if emasculated females were pollen limited. No significant effect of pollen addition or emasculation was found. Emasculated branches in the pollen-addition treatment appeared to have slightly lower seed set than non-emasculated branches that received pollen, indicating that the slight reduction in seed set was caused by emasculation rather than pollen limitation. Since stamens do not appear to be maintained as pollinator attractants, other explanations, such as genetic constraints, must be investigated. Received: 4 February 1997 / Revision accepted: 20 May 1997     

Attraction of the grasshopper, Melanoplus sanguinipes, to host plant odors and volatile components

The attraction of the polyphagous grasshopper, Melanoplus sanguinipes (F.), to odors from plant foliage or to chemical components of these odors was tested in a glass Y-tube olfactometer. Humidified air was passed at equal flow rates through a sample chamber containing plant material and an empty control chamber and then through the Y-tube to the holding chamber containing the test insect. Solutions of volatile chemicals in water were metered at a constant rate into the sample air stream with a syringe pump. Insects moving upwind were recorded after entering either the sample or control arm of the Y-tube. Both nymphs and adults were strongly attracted to the odor of chopped and intact seedling foliage of perennial ryegrass and wheat. Chopped leaves but not intact leaves of sorghum and alfalfa also were significantly attractive. The major components of ryegrass odor from both chopped and stem-cut leaves were Z-hex-3-en-1-yl acetate, Z-hex-3-en-1-ol, and pent-1-en-3-ol, in that order, with lesser amounts of E-hex-2-enal. Chopped leaves released many more minor components. The major components when tested individually or in binary and ternary mixtures were significantly attractive to grasshoppers compared to humidified air but not to the degree of whole plant odor. However, a quartenary mixture simulating the odor blend had levels of attractancy equal to that of chopped grass odor. Blends of these 5- and 6-carbon unsaturated alcohols, esters, and aldehydes volatilizing from green plants probably play an important role as olfactory cues for orientation of grasshoppers to food plants.

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Résumé L'attraction de M. sanguinipes (F.) par l'odeur du feuillage et des composés chimiques de ces odeurs a été examinée dans un olfactomètre en tube de verre en Y. Des flux identiques d'air humidifié étaient introduits dans une enceinte contenant le matériel végétal et dans une enceinte témoin, et, via le tube en Y, dans l'enceinte contenant l'insecte à étudier. Des solutions aqueuses de substances volatiles étaient introduites à un taux constant dans le courant d'air grâce à une seringue. Les insectes se déplaçant contre le vent étaient enregistrés après pénétration dans une branche déterminée du tube en Y. Larves et adultes étaient fortement attirés par l'odeur de feuillage intact ou coupé de semis de Lolium perenne et de blé (Triticum aestivum). Les feuilles coupées, mais non les feuilles intactes de sorgho (Sorghum bicolor) et de luzerne (Medicago sativa) étaient, elles aussi, significativement attractives. Les principales substances constituant de l'odeur de feuilles de Lolium perenne, tant coupées qu'intactes, étaient dans l'ordre de Z-hex-3-en-1-yl acétate, le Z-hex-3-en-1-ol et le pent-1-en-3-ol, et dans une moindre mesure, E-hex-2-enal. Les feuilles coupées libéraient beaucoup plus de composés secondaires. Les principaux constituants testés, seuls ou en mélanges binaires ou ternaires, étaient significativement attractifs, mais moins que l'odeur totale de la plante. Toutefois, un mélange quaternaire, simulant le mélange odorant, avait le même pouvoir attractif que l'odeur de la plante entière. L'union de ces alcools, esters et aldéhydes à 5- et 6-carbones non saturés, volatilisés à partir des plantes vertes, jouent probablement un grand rôle comme signaux orientateurs lors de l'attraction des criquets par leur plantes alimentaires.

     

Flowering mechanisms,pollination strategies and floral scent analyses of syntopically co‐flowering Homalomena spp. (Araceae) on Borneo

In this study, the flowering mechanisms and pollination strategies of seven species of the highly diverse genus Homalomena (Araceae) were investigated in native populations of West Sarawak, Borneo. The floral scent compositions were also recorded for six of these species. The selected taxa belong to three out of four complexes of the section Cyrtocladon (Hanneae, Giamensis and Borneensis). The species belonging to the Hanneae complex exhibited longer anthesis (53–62 h) than those of the Giamensis and Borneensis complexes (ca. 30 h). Species belonging to the Hanneae complex underwent two floral scent emission events in consecutive days, during the pistillate and staminate phases of anthesis. In species belonging to the Giamensis and Borneensis complexes, floral scent emission was only evident to the human nose during the pistillate phase. A total of 33 volatile organic compounds (VOCs) were detected in floral scent analyses of species belonging to the Hanneae complex, whereas 26 VOCs were found in samples of those belonging to the Giamensis complex. The floral scent blends contained uncommon compounds in high concentration, which could ensure pollinator discrimination. Our observations indicate that scarab beetles (Parastasia gestroi and P. nigripennis; Scarabaeidae, Rutelinae) are the pollinators of the investigated species of Homalomena, with Chaloenus schawalleri (Chrysomelidae, Galeuricinae) acting as a secondary pollinator. The pollinators utilise the inflorescence for food, mating opportunities and safe mating arena as rewards. Flower‐breeding flies (Colocasiomyia nigricauda and C. aff. heterodonta; Diptera, Drosophilidae) and terrestrial hydrophilid beetles (Cycreon sp.; Coleoptera, Hydrophilidae) were also frequently recovered from inflorescences belonging to all studied species (except H. velutipedunculata), but they probably do not act as efficient pollinators. Future studies should investigate the post‐mating isolating barriers among syntopically co‐flowering Homalomena sharing the same visiting insects.     

The effect of feeding status on sexual attractiveness of Ixodes ricinus (Acari: Ixodidae) females

Sexual attractiveness of unengorged, semiengorged and fully engorged females of both field and laboratory populations of Ixodes ricinus was studied under laboratory conditions by means of a computerised video tracking system. A male and a female were allowed to walk freely in a glass arena during 1 h and their behavioural interactions were observed. Obtained results revealed that the feeding status of I. ricinus females affects their sexual attractiveness. The highest attractiveness was observed in engorged females, the lowest in unengorged females of the field population. Copulation occurred in all experimental groups with the highest frequency observed in the unengorged virgin laboratory females. Despite engorged females being highly attractive for males on distance, the frequency of copulation was low. Differences between field and laboratory populations were found in both behavioural parameters and frequency of copulation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Semiochemical attractants for the beech leaf‐mining weevil,Orchestes fagi

The beech leaf‐mining weevil, Orchestes fagi L. (Curculionidae: Curculioninae: Rhamphini), a pest of European beech, Fagus sylvatica L. (Fagaceae), was recently discovered infesting American beech, Fagus grandifolia Ehrh., in Nova Scotia, Canada. Adult O. fagi feed on both young and mature leaves of beech as well as on other species (e.g., raspberry, Rubus spp.), but oviposition and larval feeding are restricted to beech. Females oviposit in young developing beech leaves at the time of bud burst. We characterized volatiles emitted from buds, leaves, and sapwood of American beech and examined their potential as attractants alone or when combined with other weevil pheromones for O. fagi. We predicted that adults would be attracted to volatiles emitted from beech leaves, especially those emitted from bursting beech buds. Gas chromatography/mass spectrometry (GC/MS) analyses of volatiles collected from buds at pre‐ and post‐budburst identified two diterpene hydrocarbons, 9‐geranyl‐p‐cymene ( 1 ) and 9‐geranyl‐α‐terpinene ( 2a ), that were emitted in large amounts at the time of bud burst. Compound 1 significantly increased mean catch of males and total O. fagi (but not females) on sticky traps compared with unbaited controls. Y‐tube bioassays confirmed attraction of male O. fagi to bursting beech buds and compound 1 . Attraction of male O. fagi to 1 , emitted in large quantities from American beech, is likely adaptive because both oviposition and mating of O. fagi coincide with budburst. Our data suggest that traps baited with 1 may be useful for monitoring the spread of O. fagi in North America.     

Responses of Adult Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) to Light and Combinations of Attractants and Light

Responses of adult Indianmeal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) to light alone and to a combination of attractant(s) and green/UV lights were studied. When P. interpunctella adults were given a choice between dark areas and areas illuminated with UV, green, or white light, they rested preferentially on surfaces in the illuminated areas. UV light elicited the strongest of the positive phototactic responses. Light traps were not as effective as traps baited with pheromones or food lures in capturing adult moths, and combining green or UV light with these attractants did not significantly increase the trap catches. Gravid females required a period of darkness to realize maximum oviposition, and illumination above 8 lx during the scotophase of a 24-hr light–dark cycle inhibited oviposition.     

Chemically moderated gamete preferences predict offspring fitness in a broadcast spawning invertebrate

Sperm chemoattraction, where sperm locate unfertilized eggs by following a concentration gradient of egg-derived chemoattractants, has been widely documented across numerous taxa. While marine invertebrates are favoured models for understanding the underlying mechanisms of sperm chemoattraction, the evolutionary forces underpinning the process remain enigmatic. Here, we show that in mussels (Mytilus galloprovincialis), chemically moderated gamete preferences promote assortative fertilizations between genetically compatible gametes. When offered the choice of egg clutches from two females, sperm exhibited consistent but differential ‘preferences’ for chemical cues secreted from conspecific eggs. Critically, our data reveal that the preferences shown by sperm during the egg-choice trials are highly predictive of early embryonic viability when eggs and sperm from the same individuals are mixed during standard (no-choice) fertilization assays. Moreover, we demonstrate that by experimentally separating chemoattractants from eggs, sperm swimming behaviour is differentially regulated by egg-derived chemoattractants, and that these changes in sperm behaviour are highly consistent with observed patterns of gamete preferences, fertilization and larval survival. Together, this integrated series of experiments reveals that the behaviour of sperm is fine-tuned to respond differentially to the chemical signals emitted from different conspecific eggs, and that these choices have measurable fitness benefits.