A secondary sexual character may act as an honest signal of the quality of the individual if the trait bears a cost and if its expression is phenotypically condition dependent. The cost of increasing the trait should be tolerable for individuals in good condition but not for those in a poor condition. The trait thus provides an honest signal of quality that enables the receiver to choose higher quality mates. Evidence for sex pheromones, which play a major role in shaping sexual evolution, inflicting a signaling cost is scarce. Here, we demonstrate that the amount of the major component of the pheromone in glands of Lobesia botrana (Lepidoptera) females at signaling time was significantly greater in large than in small females, that male moths preferred larger females as mates when responding to volatile signals, and small virgin females, but not large ones, exposed to conspecific pheromone, produced, when mated, significantly fewer eggs than nonexposed females. The latter indicates a condition-dependent cost of signaling. These results are in accordance with the predictions of condition-dependent honest signals. We therefore suggest that female signaling for males using sex pheromones bears a cost and thus calling may serve as honest advertisement for female quality.

Yellows diseases, caused by phytopathogenic bacteria of the genus Phytoplasma, are a major threat to grapevines worldwide. Because conventional applications against this pathogen are inefficient and disease management is highly challenging, the use of beneficial bacteria has been suggested as a biocontrol solution. A Dyella-like bacterium (DLB), isolated from the Israeli insect vector of grapevine yellows (Hyalesthes obsoletus), was suggested to be an endophyte. To test this hypothesis, the bacterium was introduced by spraying the plant leaves, and it had no apparent phytotoxicity to grapevine. Fluorescent in situ hybridization analysis showed that DLB is colonizing grapevine phloem. Because phytoplasmas inhabit the same niche, DLB interactions with this phytopathogen were examined. When the isolate was introduced to phytoplasma-infected Chardonnay plantlets, morphological disease symptoms were markedly reduced. The mode of DLB action was then tested using bioinformatics and system biology tools. DLB genome analysis suggested that the ability to reduce phytoplasma symptoms is related to inhibition of the pathogenic bacterium. These results provide the first step in examining the potential of DLB as a biological control agent against phytoplasmas in grapevine and, possibly, other agricultural crops.

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.

Vitis vinifera grapevines are susceptible to downy and powdery mildews, requiring 4 to 10 chemical treatments per season in Israel. Resistant grape varieties offer an alternative. Hybrid varieties developed by the Weinbauinstitut Freiburg were introduced in Israel for disease resistance evaluation in different climatic regions through an understanding of the resistance mechanism based on secondary metabolite profiles. Grapevines were planted across four different climatic regions in northern Israel. Key findings: (i) in the laboratory, after artificial inoculation of downy mildew, the susceptible V. vinifera variety Cabernet Sauvignon had six times more Plasmopara viticola sporangia per leaf disc than the hybrid varieties (P < 0.001). For powdery mildew, the susceptible variety had ca. 3 × 10 ⁴ more spores/cm ² leaf area than the hybrid varieties; (ii) in four tested vineyards, located in different climatic zones, downy mildew was only observed on the V. vinifera varieties; up to 4.6 times more powdery mildew incidence was observed on susceptible V. vinifera references than on the hybrid variety Cabernet Carbon, and hybrid varieties Bronner and Prior were only infected with powdery mildew on clusters, up to 33.6 times less than the reference. Souvignier Gris showed no infection in four plots over 3 years; (iii) the hybrid red grapevine varieties Prior and Cabernet Carbon showed significantly higher levels of antifungal response mediators, such as salicylic acid, than the red V. vinifera variety Tempranillo. These elevated metabolite levels correlated with increased resistance to downy and powdery mildews in the hybrids. This study advances our understanding of tolerance mechanisms in hybrid grape varieties and highlights their potential adaptation to Israel’s climate in different terroir conditions.