Spatiotemporal patterns of induced resistance and susceptibility linking diverse plant parasites.

Induced defenses mediate interactions between parasites sharing the same host plant, but the outcomes of these interactions are challenging to predict because of spatiotemporal variation in plant responses and differences in defense pathways elicited by herbivores or pathogens. Dissecting these mediating factors necessitates an approach that encompasses a diversity of parasitic feeding styles and tracks interactions over space and time. We tested indirect plant-mediated relationships across three tomato (Solanum lycopersicum) consumers: (1) the fungal pathogen-powdery mildew, Oidium neolycopersici; (2) a sap-feeding insect-silverleaf whitefly, Bemisia tabaci; and (3) a chewing insect-the leaf miner, Tuta absoluta. Further, we evaluated insect/pathogen responses on local vs. systemic leaves and over short (1 day) vs. long (4 days) time scales. Overall, we documented: (1) a bi-directional negative effect between O. neolycopersici and B. tabaci; (2) an asymmetrical negative effect of B. tabaci on T. absoluta; and (3) an asymmetrical positive effect of T. absoluta on O. neolycopersici. Spatiotemporal patterns varied depending on the species pair (e.g., whitefly effects on leaf miner performance were highly localized to the induced leaf, whereas effects on pathogen growth were both local and systemic). These results highlight the context-dependent effects of induced defenses on a diverse community of tomato parasites. Notably, the outcomes correspond to those predicted by phytohormonal theory based on feeding guild differences with key implications for the recent European invasion by T. absoluta.

Evaluation of identification methods for cryptic Bactrocera dorsalis (Diptera: Tephritidae) specimens: combining morphological and molecular techniques.

The potential for population genomics to elucidate invasion pathways of a species is limited by taxonomic identification issues. The Oriental fruit fly pest, Bactrocera dorsalis (Hendel) belongs to a complex in which several sympatric species are attracted to the same lure used in trapping and are morphologically cryptic and/or reported to hybridize. In this study, we evaluated the taxonomic ambiguity between B. dorsalis and 2 major cryptic species, based on morphological expertise and 289 target specimens sampled across the whole distribution range. Specimens were then subjected to DNA sequence analyses of the COI mitochondrial barcode and the EIF3L nuclear marker to evaluate the potential for molecular identification, in particular for specimens for which morphological identification was inconclusive. To this aim, we produced reference datasets with DNA sequences from target specimens whose morphological identification was unambiguous, which we complemented with 56 new DNA sequences from closest relatives and 76 published and curated DNA sequences of different species in the complex. After the necessary morphological observation, about 3.5% of the target dataset and 47.6% of the specimens from Southeast Asian islands displayed ambiguous character states shared with B. carambolae and/or B. occipitalis. Critical interpretation of DNA sequence data solved morphological ambiguities only when combining both mitochondrial and nuclear markers. COI discriminated B. dorsalis from 5 species; EIF3L and ITS from another species. We recommend this procedure to ensure correct identification of B. dorsalis specimens in population genetics studies and surveillance programs.

A new species of Aclees from Taiwan with notes on other species of the genus (Coleoptera: Curculionidae: Molytinae).

A molecular and morphological analysis of the species of Aclees native to Taiwan allowed for recognition of a new species, that is described here as Aclees aenigmaticus Meregalli Boriani, sp. n. The study also revealed that the species of Aclees that has been introduced into Italy and France has identical morphology and mitochondrial cox-1 gene sequence with specimens of A. taiwanensis from Taiwan. Taiwan is thus assumed to be the country of origin of the specimens introduced into Europe. A key to the species of Aclees present in Taiwan is provided. A lectotype is designated for Aclees foveatus Voss, 1932, and some remarks on A. hirayamai Kôno, 1932 are given. Pagiophloeus visayus Heller, 1929 from the Philippines is transferred to the genus Aclees, comb. n.

Bark beetles and pinhole borers recently or newly introduced to France (Coleoptera: Curculionidae, Scolytinae and Platypodinae).

We present an annotated list of 11 Scolytinae and Platypodinae species newly or recently introduced to France. Four species are recorded for the first time as interceptions: Euplatypus hintzi (Schaufuss), Euplatypus parallelus (Fabricius), Xyleborus affinis Eichhoff and Xyleborus ferrugineus (Fabricius). Two are possibly naturalised: Xyleborus bispinatus Eichhoff and Cryphalus dilutus Eichhoff, while Cyclorhipidion distinguendum (Eggers) and Xyloterinus politus (Say) are confirmed as species newly established in Europe. Moreover, an unidentified species of Amasa Lea, collected previously in Spain, is recorded for the first time in France: Amasa sp. near truncata (Erichson). We point out that literature references to Amasa truncata as an invasive species in New Zealand and South America are incorrect, as the photographs of these non-native populations do not match the holotype of A. truncata. For each species we have updated its global distribution, detailed all French records, and summarized biology, ecology, host trees and potential risks as pests.

Banning of methyl bromide for seed treatment: could Ditylenchus dipsaci again become a major threat to alfalfa production in Europe?

In Europe, the stem and bulb nematode Ditylenchus dipsaci has been listed as a quarantine pest by EPPO: without any control, it may cause complete failure of alfalfa crops. Movement of nematodes associated with seeds is considered to be the highest-risk pathway for the spread of this pest. Since the 2010 official withdrawal of methyl bromide in Europe, and in the absence of any alternative chemical, fumigation of contaminated seed batches is no longer possible, which makes the production of nematode-free alfalfa seeds difficult to achieve and leads to unmarketable seed batches. Thermotherapy is being considered as a realistic alternative strategy, but its efficiency still remains to be validated. The combination of the currently available methods (i.e. use of resistant cultivars, seed production according to a certification scheme, mechanical sieving, seed batch inspection) could significantly reduce the likelihood of seed contamination. However, it does not guarantee a total eradication of the nematode. Although it is already widely distributed all over Europe, reclassification of D. dipsaci as a regulated non-quarantine pest to reduce the possibility of further introductions and the rate of spread of this pest appears to be a risky strategy because of the lack of up-to-date documented data to evaluate damage thresholds and determine acceptable tolerance levels.

Phytophagous arthropods and a pathogen sharing a host plant: evidence for indirect plant-mediated interactions.

In ecological systems, indirect interactions between plant pathogens and phytophagous arthropods can arise when infestation by a first attacker alters the common host plant so that although a second attacker could be spatially or temporally separated from the first one, the former could be affected. The induction of plant defense reactions leading to the production of secondary metabolites is thought to have an important role since it involves antagonistic and/or synergistic cross-talks that may determine the outcome of such interactions. We carried out experiments under controlled conditions on young rose plants in order to assess the impact of these indirect interactions on life history traits of three pests: the necrotrophic fungus Botrytis cinerea Pers.: Fr. (Helotiales: Sclerotiniaceae), the aphid Rhodobium porosum Sanderson (Hemiptera: Aphididae) and the thrips Frankliniella occidentalis Pergande (Thysanoptera: Thripidae). Our results indicated (i) a bi-directional negative interaction between B. cinerea and R. porosum, which is conveyed by decreased aphid growth rate and reduced fungal lesion area, as well as (ii) an indirect negative effect of B. cinerea on insect behavior. No indirect effect was observed between thrips and aphids. This research highlights several complex interactions that may be involved in structuring herbivore and plant pathogen communities within natural and managed ecosystems.