Alfio Raspi

(Z)-9-tricosene identified in rectal gland extracts of Bactrocera oleae males: first evidence of a male-produced female attractant in olive fruit fly.

It is well-known that Bactrocera oleae (olive fruit fly) females attract conspecific males by using 1,7-dioxaspiro[5,5]undecane (1) as the main component of their sex pheromone, and that 1 is produced in the female rectal gland. Although some authors have claimed that B. oleae males also attract females, to date no male-produced female attractants have been found in this species. In this paper, we report the first identification of a substance unique to males and able to attract females. The findings of the study include the following: (1) females responded in a bioassay to hexane extracts obtained from rectal glands of 15-day-old B. oleae males, (2) the presence of (Z)-9-tricosene (2) was consistently and unambiguously identified in these extracts using gas chromatography (GC) and GC-mass spectrometry methods, (3) in preliminary bioactivity tests, low doses (equivalent to a few males) of chemically and stereoisomerically pure synthetic (Z)-9-tricosene (2) attracted olive fruit fly females. Interestingly, compound 2, commonly called muscalure, is also a well-known component of the house fly (Musca domestica) sex pheromone.

Male Wing Vibration in the Mating Behavior of the Olive Fruit Fly Bactrocera oleae (Rossi) (Diptera: Tephritidae)

The olive fruit fly, Bactrocera oleae (Diptera: Tephritidae), is a worldwide pest of olive fruits. To date, the mating behavior of this tephritid has not been fully clarified. Little has been reported regarding the characteristics and behavioral role of B. oleae male wing vibration. This study provides a detailed description of male wing vibration, recorded by a high-speed video camera and compared with a frame-by-frame analysis, prior to successful and unsuccessful matings. Experimental evidence is given of the importance of male wing vibration during courtship for successful mating. Firstly, when the males did not perform wing vibration, but simply jumped onto the female and immediately attempted to copulate, no successful matings were registered. Secondly, when the male’s wings were removed, the probability of successful mating was significantly reduced. Thirdly, the frequency and pulse duration of the male wing vibration during courtship were higher in successful matings than in unsuccessful ones. Lastly, a wing sexual dimorphism was found: length and total wing area were significantly higher among males. Overall, our research increases the knowledge of the reproductive behavior of B. oleae, by suggesting the importance of wing vibration among the range of sensory modalities used by this tephritid in sexual communication.

The production of female sex pheromone in Bactrocera oleae (Rossi) young males does not influence their mating chances

In Bactrocera oleae females attract males, which is in contrast to the majority of Tephritidae. However, the major component of the secretion of the female rectal ampulla glands, 1,7‐dioxaspiro‐[5,5]‐undecane (DSU), was also isolated from the glands of young males. The DSU produced by females and young males attracts males, but not females. In this study, we investigated the role of the production of DSU in young males. The mating performances of young and old males were evaluated, as well as the male‐male courtships by old males oriented at young and old males. Young males were found not to have a mating advantage. Young males were courted more by other males. Frame‐by‐frame analysis of male wing vibrations showed that this behavior did not differ when oriented at females and young males, highlighting that young males are perceived as females by the courting males. Overall, the production of DSU in young B. oleae males did not seem to be a case of female chemical mimicry. The hypothesis that young olive fruit fly males could benefit indirectly from the DSU production, simply distracting mature males away from females, is discussed.

Behavioural and electrophysiological responses of the olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), to male- and female-borne sex attractants

In the olive fruit fly, Bactrocera oleae, females attract males by producing 1,7-dioxaspiro[5.5]undecane (olean), the main component of the sex pheromone secreted by rectal glands. It has been recently demonstrated that males are able to produce (Z)-9-tricosene (muscalure) in rectal glands, a compound that selectively attracts females. In this study, a male grooming reaction that may transfer the male-borne compounds from rectal to urotergal glands was observed, suggesting that urotergal glands could be involved in B. oleae sexual communication. GC/MS, EAG, GC/EAD analyses and behavioural assays were carried out to compare the role of male rectal and urotergal glands during courtship. In both male glands, olean and muscalure amounts were age dependent. Extracts of rectal glands contained higher amounts of olean and/or muscalure than urotergal ones. Extracts of rectal and urotergal glands of males and females elicited EAG responses in both sexes. GC/EAD showed that female EAG response to male rectal extracts was mainly due to olean and muscalure. Synthetic compounds evoked EAG dose-dependent responses in both sexes, and the EAG response to muscalure was higher as compared to olean. Rectal and urotergal glands from old males were able to attract females, while urotergal glands from young males attracted only males. Overall, our results add knowledge to the mating system of B. oleae, giving first evidences on the electrophysiological activity of muscalure towards both sexes, as well as on the involvement of male urotergal glands in the chemical sexual communication of this pest.

Dimethyl disulfide and dimethyl trisulfide: so similar yet so different in evoking biological responses in saprophilous flies

Dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) are used by saprophilous insects to locate breeding sites (decaying organic matter), and by brood-site deceptive flowers to attract such insects. However, little is known about the relative importance of these two compounds in eliciting electrophysiological and behavioral responses in the insects. Here, we compared the relative attractiveness of DMDS and DMTS to saprophilous flies in field choice experiments and tested whether potential differences in field responses can be explained by differences in electrophysiological antennal responses to these compounds. Field experiments revealed that the attractiveness of a mixture of these compounds is due to DMTS alone. This result was confirmed by electroantennographic recordings in which flies of four tested species of Calliphoridae (Lucilia sericata, L. caesar,Calliphora vicina,Protocalliphora azurea) and one Muscidae (Musca domestica) respond clearly to DMTS, but not to DMDS. In house flies, however, DMTS elicited electrophysiological responses only, not reflected in behavioral assays. Despite the fact that DMTS and DMDS exhibit similar chemical structures, both the electroantennographic and field responses from saprophilous flies to these two compounds strongly differed. Our study suggests that oligosulfide-responsive saprophilous flies rely on DMTS and not DMDS for finding appropriate breeding sites and that DMTS and not DMDS could act as a key mediator for pollinator attraction in brood-site deceptive plants.

First records of pollinators of two co-occurring Mediterranean Apocynaceae

Abstract This article presents results of a field survey of pollinators of two Apocynaceae, Periploca laevigata subsp. angustifolia (Labill.) Markgraf (Periplocoideae) and Caralluma europaea (Guss.) N.E.Br. (Asclepiadoideae) co-occurring on Lampedusa Island, Mediterranean sea. Fifteen species within nine families of Diptera have been identified as pollinators of the two plants. The families involved are Tephritidae, Milichiidae, Trixoscelididae, Scathophagidae, Anthomyiidae, Muscidae, Calliphoridae, Sarcophagidae, Rhinophoridae. Families of Muscidae and Sarcophagidae are the more represented, respectively with four and three species. P. laevigata subsp. angustifolia seems to have a broader spectrum of pollinators, with 12 species of Diptera involved, while C. europaea has 8 species of Diptera as pollinators. Five species of Diptera are shared between the two plant species. The presented data are the first records of pollinators for P. laevigata subsp. angustifolia and C. europaea and confirm that both taxa are fly pollinated, though they do not conform exactly to the sapromyiophilous syndrome. The number of pollinators identified indicated that the morphological and functional floral specialization of the two taxa cover a wide number of pollinators with a similar biology.

For sex and more: attraction of the tephritid parasitoid Psyttalia concolor (Hymenoptera: Braconidae) to male sex pheromone of the olive fruit fly, Bactrocera oleae

The braconid parasitoid Psyttalia concolor foraging for larvae of Bactrocera oleae (Diptera: Tephritidae) uses olfactory cues from the larval microhabitat. However, it could rely on the sex pheromones of adults of its host, since B. oleae mating leks usually occur on olive plants and a high number of infested fruits can be easily located in their close proximity. We quantified the behavioural responses of P. concolor towards different doses of the two major sex pheromone components of B. oleae, the female-borne 1,7-dioxaspiro[5.5]undecane (DSU) and the male-borne (Z)-9-tricosene (ZT). Results showed that P. concolor females and males were attracted only to the highest amounts of ZT (10 B. oleae male equivalents), regardless of the mating status. Wasps remained longer on the surfaces treated with high ZT amounts over the control. P. concolor females could exploit the ZT produced by lekking olive fruit fly males as a foraging kairomone. This could allow them to rapidly track B. oleae-infested olive plants, thus raising their chances to locate host larvae during their lifespan. On the other hand, the perception of ZT by P. concolor males could raise their chances to locate receptive females emerging from parasitised B. oleae pupae or also ovipositing in olive fruits. This study increases the knowledge of the reproductive biology of P. concolor, highlighting a case of chemical espionage in which a sex pheromone component from adult stages of the host is exploited both as a foraging kairomone by female parasitoids and as a sexual kairomone by male wasps.

Insect pollinators of the late winter flowering Rhamnus alaternus L., a candidate for honeybee-friendly scrubland spots in intensively managed agricultural areas

Insect pollinators of Rhamnus alaternus belong to 11 families, 17 genera and 20 species. The most abundant species is the honeybee followed by flies and bumblebees. Honeybee visits on R. alaternus decreased from late winter to early spring, highlighting the key role of this flowering in food paucity periods.

LEARNING BEHAVIOUR OF OPIUS CONCOLOR SZLEPLIGETI (HYMENOPTERA: BRACONIDAE) IN HOST DISCRIMINATION

Abstract Laboratory experiment on learning behaviour of Opius concolor in host discrimination was conducted. The superparasitism by both the “inexperienced” and “experienced” wasps at the highest ratio of parasitoid: host (1: 0. 9) was significantly higher than those at two low ratios (1: 5 and 1: 10). The distributions of the eggs of O. concolor females in hosts examined by dissection showed that the eggs laid by both “inexperienced” and “experienced females” at 1: 0. 9 ratio did not agree with the Poisson distribution. However, at 1: 5 ratfio the eggs laid by “experienced” ones did not agree with Poisson distribution, whereas by inexperienced ones agreed with Poisson distribution. On the contrary. the eggs laid both by “inexperienced” and “experienced” wasps at 1: 10 ratio agreed with the Poisson distribution. The results of experiment on the self‐superparasitism indicated that both “experienced” and “inexperienced” single females, in 6 h at ratio 1: 5, could carry out on superparasitization.