Rakefet Sharon

Vitex agnus-castus is a Preferred Host Plant for Hyalesthes obsoletus

Hyalesthes obsoletus Signoret (Homoptera: Cixiidae) is a polyphagous planthopper that transmits stolbur phytoplasma (a causative agent of “yellows” disease) to various weeds, members of the Solanaceae, and wine grapes (Vitis vinifera L.) in Europe and the Middle East. Planthoppers were collected by hand vacuuming eight native plant species. Vitex agnus-castus L., a shrub in the Verbenaceae, hosted the largest number of H. obsoletus, although Olea europaea L. also served as a host for adults. Using a Y-olfactometer, we compared the planthoppers relative preference for V. agnus-castus, Convolvulus arvensis, and V. vinifera. V. agnus-castus was more attractive to both male and female H. obsoletus than the other plants. H. obsoletus antennal response was stronger to volatiles collected from V. agnus-castus than from Cabernet Sauvignon variety of V. vinifera. To determine if V. agnus-castus would serve as a reservoir for the pathogen, H. obsoletus were collected from leaf and stem samples of native V. agnus-castus, and were tested by polymerase chain reaction (PCR) for the presence of phytoplasma DNA. While 14% and 25% (2003 and 2004, respectively) of the insects tested positive for phytoplasma DNA, none of the plant samples tested positive. To determine if V. agnus-castus could serve as a host plant for the development of the planthopper, we placed emergence cages beneath field shrubs and enclosed wild-caught H. obsoletus in a cage with a potted young shrub. We found adult H. obsoletus in the emergence cases and planthopper nymphs in the soil of the potted plant. We concluded that V. agnus-castus is attractive to H. obsoletus, which seems to be refractory to phytoplasma infections and warrants further testing as a trap plant near vineyards.

The effect of grape vine cultivars on Lobesia botrana (Lepidoptera: Tortricidae) population levels.

The European vine moth Lobesia botrana Denis & Schiff. (Lepidoptera: Tortricidae) is a key pest in the vineyards of Israel and Europe. Traps baited with the female sex pheromone are commonly used to monitor the pest population. However, the role of the vine cultivars on monitoring the moth population using pheromone-baited traps was not yet studied. The present study aimed to identify the effect of grape cultivars on L. botrana adult distribution patterns in the field, in order to achieve a better understanding of the monitored data in respect to male and female’s host preference. The 3-year study in commercial vineyards used four cultivars: Carignan, Emerald Riesling, French Colombard, and Cabernet Sauvignon. The moth population of each generation was estimated from male counts in pheromone traps; three generations were observed in all experimental orchards, each year. Female host choice was studied by monitoring freshly deposited eggs and newly hatched larvae on vines. The study showed a significant effect of cultivar on numbers of trapped males in most years, and a cultivar effect on female host choice. For both males and females and for all phenological stages of the grapes, Carignan and French Colombard attracted the most and Cabernet Sauvignon the fewest specimens. The results show that cultivar blend within the vineyard can affect the distribution pattern of the pest. Knowledge of the expected choice of the female moth, and of the timing of its decision could lead to an improved monitoring system, with the preferred cultivar as an indicator.

Mating disruption method against the vine mealybug, Planococcus ficus: effect of sequential treatment on infested vines

The vine mealybug, Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), is a major pest of vineyards. Here, we tested the efficacy of the mating disruption method against the pest when applied during one or two successive years in high and low infestation levels. Following 1 year of treatment, at low initial infestation levels a shutdown of pheromone traps was observed, along with a significant reduction in infested vines. With initially high infestation levels, a gradual reduction in infested vines was observed, with a trap shutdown seen only after the second year of pheromone application. We discuss the implications of the male mating disruption method for this pest in which the wingless females are aggregated with limited movement among vines, offering multiple mating opportunities for the flying male.

Characterisation of pre-service teachers' attitude to feedback in a wiki-environment framework

This is a two-phase research process in a wiki environment. The first phase explored (1) the significance of peer-feedback on students’ academic performance on a specific task in a wiki environment, (2) three types of peer-feedback and (3) students’ constraints on offering meaningful feedback to their peers. The objective of phase two was to determine the reasons why students refrain from peer-feedback. Significant correlation exists between the willingness to give feedback and the willingness to receive feedback. Significant correlation also exists between the difficulty of giving feedback and the difficulty of receiving feedback. Female students tend to consider feedback as the teachers responsibility more than male students. Religious beliefs did not have any significant effect on any of the parameters tested. The results indicate that traditional students tend to be more conservative regarding feedback. There are worrying implications to pre-service teachers’ refraining from giving feedback.

Bacterial associates of Hyalesthes obsoletus (Hemiptera: Cixiidae), the insect vector of bois noir disease, with a focus on cultivable bacteria.

The planthopper Hyalesthes obsoletus (Hemiptera: Cixiidae) is an important vector of phytoplasma diseases in grapevine. In the current study, the bacterial community compositions of symbionts of this insect were examined. Two dominant bacterial lineages were identified by mass sequencing: the obligate symbiont Candidatus Sulcia, and a facultative symbiont that is closely related to Pectobacterium sp. and to BEV, a cultivable symbiont of another phytoplasma vector, the leafhopper Euscelidius variegatus. In addition, one bacterium was successfully isolated in this study - a member of the family Xanthomonadaceae that is most closely related to the genus Dyella. This Dyella-like bacterium (DLB) was detected by FISH analysis in H. obsoletus guts but not ovaries, and its prevalence in H. obsoletus increased during the fall, suggesting that it was acquired by the host through feeding. We found that DLB inhibits Spiroplasma melliferum, a cultivable relative of phytoplasma, suggesting that it is a potential candidate for biological control against phytoplasma in grapevines.

Manipulation of Insect Reproductive Systems as a Tool in Pest Control

Insect pests must reproduce in order to exist. In sexual organisms, sperm and ova need to synchronically meet in a specific environment under conditions that may include temperature, time, food, day length, and many others. Mating events can therefore be predicted and as such open for manipulation.

Trap plants reduces grapevine yellows disease incidence in commercial vineyards

The host plant Vitex agnus-castus attractiveness to the “stolbur” phytoplasma vector Hyalesthes obsoletus was exploited to study application methods of trap plants in order to reduce yellows disease incidence in vineyards. Following the introduction of the trap plants in vineyards, infestation level was reduced. The effect on plot infestation level diminishes with distance from trap plants and varies depending on the trap plant biomass. There is also indication of trap plant effect joined with wind direction. The grapevine yellows disease can be controlled in Israel conditions by means of trap plants that lure the vector.

The source plant for phytoplasmas in the Israeli vineyards is still a mystery

The fact that phytoplasma could not be detected in Vitex agnus-castus which is the preferred host of the insect vector, suggested that other plant species are involved. Israeli vineyards and surroundings were surveyed. Samples from grapevines, wild and cultivated species were analysed. To confirm the presence of phytoplasma, DNA was extracted and amplified using general phytoplasma ribosomal primers and specific tub primers. Phytoplasma tuf-type was identified by PCR/RFLP analyses. The results show that “stolbur” phytoplasma tuf-type b is the only type that was detected in symptomatic grapevines but it was not detected in any other plant species that was sampled. In V. agnus-castus, Convolvulus, Urtica and Crepis, considered as potential host plants, peanut witches’ broom (16SrII) or pigeon pea witches’ broom (16SrIX) related phytoplasmas were detected in 2.8–23% of the samples. Consequently, the source plant for “stolbur” phytoplasma in vineyards remains unknown.