Roxana L. Minuz

Perception of Host Plant Volatiles in Hyalesthes obsoletus: Behavior, Morphology, and Electrophysiology

The Palearctic planthopper Hyalesthes obsoletus is the natural vector of the grapevine yellow disease Bois noir. Grapevine is an occasional host plant of this polyphagous planthopper. To deepen our knowledge of the role of plant volatile organic compounds for H. obsoletus host plant searching, we carried out behavioral, morphological, and electrophysiological studies. We tested the attraction of H. obsoletus to nettle, field bindweed, hedge bindweed, chaste tree, and grapevine by using a Y-shaped olfactometer. The results showed a significant attraction of male H. obsoletus to chaste tree, and of the females to nettle. Male H. obsoletus were repelled by odor from hedge bindweed. Ultrastructural studies of the antennae showed at least two types of olfactory sensilla at the antennal pedicel: plaque organs and trichoid sensilla. Volatile organic compounds from nettle and chaste tree were collected, and the extracts were analyzed by coupling gas-chromatography to both mass-spectrometry and electroantennography. The volatile organic compounds that elicited electrophysiological responses in male and female antennae were identified. These findings are discussed with respect to behavior of H. obsoletus males and females in the field.

Lures for red palm weevil trapping systems: aggregation pheromone and synthetic kairomone.

BACKGROUND The optimisation of the lure is essential for the implementation of trapping systems to control insect pests. In this work, the response of the red palm weevil (RPW), Rhynchophorus ferrugineus Olivier, to increasing emission rates of its aggregation pheromone (ferrugineol) and the efficacy of a convenient synthetic kairomone based on fermentation odours (ethyl acetate and ethanol) have been evaluated in different years and locations along the Mediterranean basin. RESULTS In general, although capture data and emission had noticeable variability among locations, significantly fewer RPW were captured in pyramidal Picusan® traps with the lowest ferrugineol emission rates tested (0.6-3.8 mg day-1 ). Captures increased rapidly with ferrugineol emission up to 4-5 mg day-1 ; then, higher emission rates did not improve or reduce captures, up to the highest emission rate tested of 50.9 mg day-1 . Thus, there is no evidence of an optimum release rate corresponding to a maximum of RPW catches. Traps baited with the synthetic kairomone (1:3 ethyl acetate/ethanol) captured 1.4-2.2 times more total weevils than traps baited only with ferrugineol. Moreover, in most of the locations, the synthetic blend was at least as effective as the local coattractants used (plant material + molasses). CONCLUSIONS Ferrugineol emission rate can vary in a wide range without significantly affecting RPW response. Coattractants based on fermenting compounds, ethyl acetate and ethanol, are able to improve the attractant level of ferrugineol and could be employed to replace non-standardised natural kairomones in RPW trapping systems after further optimisation of their proportions and doses.

Perching mate-locating strategy in Paysandisia archon (Lepidoptera: Castniidae): behavioral and morpho-physiological investigations.

ABSTRACT We studied Paysandisia archon (Burmeister) (Lepidoptera: Castniidae: Castniinae) courtship behavior to provide a detailed qualitative and quantitative description of male and female behaviors. Moreover, to investigate the role of antennal olfaction and visual stimuli in mate-recognition, bio assays with antennectomized adults and dummies were performed. To assess the presence of a pheromone gland in the ovipositor, morphological (using light and scanning electron microscopic techniques), electrophysiological, and chemical investigations were carried out. We observed perching mate-locating behavior of P. archon males, with the female triggering the courtship sequence by approaching the perching male first. The stereotyped courtship sequence is made up of five main steps: female flight, pair flight, alighting close, copulation attempt, and clasping. Our findings suggest that visual cues are important in P. archon courtship behavior, and the role of chemical cues is also discussed. Moreover, we observed a higher antenna cleaning frequency in females than in males. Ovipositor extrusions during courtship appeared not to be related to calling behavior, and histological investigations showed no evidence of glandular tissues involved in sex pheromone production. The P. archon ovipositor consists of the eighth uromere, which forms the ovipositor base, and the 9th and 10th uromeres are fused together and connected to the base by an intersegmental membrane. Overall, 24 compounds were identified from extracts obtained from ovipositors: 9 compounds were detected only in extracts from the ovipositors of 24-h-old virgin females, and not from those of 1-h-old females. None of these compounds elicited any significant electrophysiological responses from male antennae.

Sex-Dispersal Differences of Four Phloem-Feeding Vectors and Their Relationship to Wild-Plant Abundance in Vineyard Agroecosystems

ABSTRACT Sex-dispersal differences of four phloem-feeding vectors and their relationship to wild-plant abundance were analyzed over 2 yr in two vineyard agroecosystems. Adults of Euscelis lineolatus Brullè, Neoaliturus fenestratus (Herrich-Schäffer), Psammotettix alienus (Dahlbom), and Hyalesthes obsoletus Signoret were sampled by using yellow sticky traps at two heights (20 and 150 cm) above the ground in a regular geo-referenced grid. Wild vegetation was surveyed around each sampling point. The most abundant species collected was N. fenestratus, followed by P. alienus, H. obsoletus, and E. lineolatus. Low traps were more effective in capturing the females of N. fenestratus and P. alienus and the males of all of the species, except N. fenestratus at one site. Sex ratio was male-biased for N. fenestratus in both agroecosystems at both trap heights, and only in low traps for H. obsoletus and P. alienus at one site. Insect abundance, temporal population dynamics, and dispersal patterns showed considerable fluctuations according to vineyard agroecosystems and years. In the current study, all of the four phloem-feeding vectors were not found homogeneously in the vineyards, and they were aggregated in correspondence with their herbaceous wild-plant hosts. Insects tended to disperse from the borders toward the vineyard, or vice versa. Colonizing pattern was strongly affected by border vegetation, fallow fields, and vineyard ground-cover vegetation. Different plant communities were identified inside the agroecosystems, and significant correlations among insect and plant-species abundances were recorded. Data highlight the importance of understanding the dispersal patterns of vector species for the application of correct integrated pest-management strategies.

Anatomy of the antennal dorsal organ in female of Neodryinus typhlocybae (Hymenoptera: Dryinidae): A peculiar sensory structure possibly involved in perception of host vibration

Neodryinus typhlocybae (Hymenoptera: Dryinidae) is a natural enemy of the planthopper Metcalfa pruinosa, which was introduced from North America into Europe and has become established in various regions as a pest species. Vibrational signals play a crucial role in the communication of M. pruinosa, which appears to be exploited by N. typhlocybae. Scanning and transmission electron microscopy have shown that the antennae of N. typhlocybae females have peculiar and complex sensory structures: deep longitudinal grooves that house long sensilla trichodea, termed here “Antennal Dorsal Organs.” Such structures were not present on male antennae. These sensilla extend for the length of the grooves, without contact with the groove cuticle. Their hair shaft is empty and aporous, and inserted into a specialized socket, underneath which there is a cuticular ampulla‐like chamber. Each sensillum is associated with two sensory neurons: one terminates at the proximal end of the dendritic sheath; the other continues into the sensillum sinus and is enclosed in the dendritic sheath. This second sensory neuron then enters the ampulla‐like chamber through the circular opening, and then terminates with a conspicuous tubular body at the shaft base. The possible involvement of this peculiar structure in the context of host recognition mechanism is discussed. J. Morphol. 277:128–137, 2016.

Behavioral responses of Hyalesthes obsoletus to host-plant volatiles cues

The polyphagous planthopper Hyalesthes obsoletus Signoret is considered to be the principal vector of stolbur phytoplasma, which is associated with yellow diseases of grapevine. To explore the possibility of developing novel control strategies, the behavioral responses to six synthetic mixtures and nine single compounds, previously identified from the headspace of Vitex agnus-castus L. (chaste tree) and Urtica dioica L. (nettle), were investigated in Y-tube bioassays. Choice tests revealed differences in the behavioral responses of males and females to the volatiles that they were exposed to. Males were attracted to a mixture containing (E)-β-caryophyllene, 1,8-cineole, (E,E)-α-farnesene, (E)-β-farnesene, and methyl salicylate (mixture 2). The addition of methyl benzoate to this five-compound mixture (mixture 3) did not attract males but elicited positive responses in females. Furthermore, females were attracted to a mixture containing (E)-β-caryophyllene, (E,E)-α-farnesene, (Z)-3-hexenyl acetate, (Z)-3-hexen-1-ol, and benzothiazole (mixture 4), but here addition of methyl salicylate (mixture 5) did not attract females. Neither males nor females showed attractivity or repellency toward the singly tested compounds. This study enhances knowledge on the interaction of insect behaviorally effective constituents in complex plant volatile mixtures. The attractive mixtures of plant volatiles identified suggest the possibility of using them in monitoring and management of H. obsoletus.