Torymus sinensis and its close relatives in Europe: a multilocus phylogeny, detailed morphological analysis, and identification key

The introduction of the biological control agent Torymus sinensis Kamijo (Hymenoptera, Chalcidoidea, Torymidae) to control the populations of the chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera, Cynipidae) is considered one of the successful programs in biological control. The species was involved in interspecific hybridisation in Japan and the specimens imported into Europe were derived from this hybrid lineage, showing signs of introgression. The discovery of mitochondrial haplotypes or possible Enolase haplotypes from T. beneficus or of specimens with shorter ovipositor does not necessarily imply that T. beneficus is present in Europe, only that the European specimens are of hybrid origin. Of the native European Torymus species associated with D. kuriphilus, the molecular and morphometric results indicate Torymus notatus (Walker) as the closest species to T. sinensis. The two are part of the same species-group (cyaneus group), are nested together in the multivariate ratio analysis and are the closest genetically based on all three nuclear markers: Enolase (1.5% divergence), Wingless (2%) and ITS2 (13%). However, on the mitochondrial marker COI the closest species is Torymus rubi (Schrank) at 9.9% divergence. As such, T. notatus is the most likely candidate for accidental interspecific hybridisation if this is to happen in Europe. We provide an illustrated identification key for the European species of Torymus associated with D. kuriphilus, an important but lacking tool for biological control programs

Evidence for a cryptic parasitoid species reveals its suitability as a biological control agent.

Uncertainty about the taxonomic status and the specificity of a species commonly prevent its consideration as a candidate for biological control of pest organisms. Here we use a combination of molecular analysis and crossing experiments to gather evidence that the parasitoid wasp Ganaspis brasiliensis, a candidate for biological control of the invasive spotted wing drosophila Drosophila suzukii, is a complex of at least two cryptic species. Complementary experiments demonstrate that individuals from one genetic group readily parasitize several drosophila species regardless of their food source while individuals from the other one are almost exclusively specific to larvae feeding in ripening fruits. Because only D. suzukii attacks ripening fruits in its area of invasion, parasitoids from this second group appear to be well suited as a biological control agent. Our study demonstrates the need for a combination of biosystematics with biological and ecological investigations for the development of safe and efficient biological control programs

Guidelines and framework to assess the feasibility of starting pre-emptive risk assessment of classical biological control agents

Non-native invasive arthropod species threaten biodiversity and food security worldwide, resulting in substantial economic, environmental, social and cultural costs. Classical biological control (CBC) is regarded as a cost-effective component of integrated pest management programmes to manage invasive arthropod pests sustainably. However, CBC programmes are traditionally conducted once a pest has established in a new environment, and invariably all research needed to achieve approval to release a biological control agent can take several years. During that time, adverse impacts of the pest accelerate. A pre-emptive biocontrol approach will provide the opportunity to develop CBC for invasive pests before they arrive in the country at risk of introduction and therefore enhance preparedness. A critical aspect of this approach is that risk assessment is carried out in advance of the arrival of the pest. Implementing pre-emptive biocontrol risk assessment means that natural enemies can be selected, screened in containment or abroad and potentially pre-approved prior to a pest establishing in the country at risk, thus improving CBC effectiveness. However, such an approach may not always be feasible. This contribution defines the fundamental prerequisites, principles, and objectives of pre-emptive biocontrol risk assessment. A set of guidelines and a decision framework were developed, which can be used to assess the feasibility of conducting a pre-emptive risk assessment for candidate biological control agents against high-risk arthropod pest

A Whole-Genome Scan for Association With Invasion Success in the Fruit Fly Drosophila Suzukii Using Contrasts of Allele Frequencies Corrected for Population Structure

Evidence is accumulating that evolutionary changes are not only common during biological invasions but may also contribute directly to invasion success. The genomic basis of such changes is still largely unexplored. Yet, understanding the genomic response to invasion may help to predict the conditions under which invasiveness can be enhanced or suppressed. Here, we characterized the genome response of the spotted wing drosophila Drosophila suzukii during the worldwide invasion of this pest insect species, by conducting a genome-wide association study to identify genes involved in adaptive processes during invasion. Genomic data from 22 population samples were analyzed to detect genetic variants associated with the status (invasive versus native) of the sampled populations based on a newly developed statistic, we called C2, that contrasts allele frequencies corrected for population structure. We evaluated this new statistical framework using simulated data sets and implemented it in an upgraded version of the program BAYPASS. We identified a relatively small set of single-nucleotide polymorphisms that show a highly significant association with the invasive status of D. suzukii populations. In particular, two genes, RhoGEF64C and cpo, contained single-nucleotide polymorphisms significantly associated with the invasive status in the two separate main invasion routes of D. suzukii. Our methodological approaches can be applied to any other invasive species, and more generally to any evolutionary model for species characterized by nonequilibrium demographic conditions for which binary covariables of interest can be defined at the population level

Life-history traits of <em>Encarsia guadeloupae</em>, a natural enemy of the invasive spiralling whitefly <em>Aleurodicus dispersus</em>

International audienceOn south-west Indian Ocean islands, many crops and ornamental plants are threatened by the spiralling whitefly Aleurodicus dispersus (Hemiptera: Aleyrodidae), which is a polyphagous pest that is native to the Caribbean region. Aleurodicus dispersus causes economic damage to various crops on all the islands in the south-west Indian Ocean. The hymenopteran parasitoid Encarsia guadeloupae (Hymenoptera: Aphelinidae) is a natural enemy of A.dispersus on the Caribbean islands. In this study, we assessed the geographical distribution of the parasitoid in La Reunion, an island in the south-west Indian Ocean where the parasitoid was first observed in 2004. We also investigated its main life-history traits. Field surveys indicated that the parasitoid is widespread in most of the low-lying areas of the island and exhibits high parasitism rates on A.dispersus populations. At 25 degrees C, E.guadeloupae adults had a mean longevity of 33.6days, and its pre-imaginal development required 23days. The lower temperature threshold and thermal constant were estimated to be 7.9 degrees C and 132 degree-days, respectively. Females of E.guadeloupae preferred to deposit eggs in early rather than in late instars of A.dispersus, and oviposition rates were highest in the second larval instar. Females of E.guadeloupae were able to oviposit in larvae of other species of whiteflies found in La Reunion (Bemisia tabaci and Dialeurolonga simplex), although subsequent development of the parasitoid was not monitored. Finally, we discuss the potential use of E.guadeloupae for the control of whitefly populations on islands in the south-west Indian Ocean

Field monitoring of <em>Drosophila suzukii</em> and associated communities in south eastern france as a Pre-requisite for classical biological control

International audienceThe spotted wing Drosophila, Drosophila suzukii (Ds), became a major economic pest for fruit production since its establishment in Europe and America. Among potential control methods, only classical biological control appears to be a mean of sustainably regulating Ds in both cultivated and natural habitats. In the frame of risk assessment, pre-release surveys were carried out in a restricted but highly heterogeneous area in the south-east of France using traps and deliberate field exposures of Ds and D. melanogaster larvae/pupae. Although Ds abundance varied according to sampling methods, it was found to be pervasive and to produce offspring and adults in most conditions (spatial and seasonal). Its main limits are some specific abiotic conditions (i.e., desiccation) as well as interspecific competition. Indeed, Ds mostly co-occurred with D. busckii and D. hydei, probably due to common phenology and/or ecological requirements. These two species thus deserve more attention for risk assessment. The main indigenous parasitoids collected belonged to two pupal species, Trichopria cf drosophilae and Pachycrepoideus vindemmiae, but their presence was observed late in the autumn and mainly in cultivated areas. Results are discussed in a comparison of the methodological approaches for monitoring Drosophilids and the benefits-risks assessment of classical biological control

Differential influence of temperature on the toxicity of three insecticides against the codling moth Cydia pomonella (L.) and two natural enemies

International audienceInsecticide toxicity may strongly vary with temperature, and interspecific differences have been commonly reported for this relationship. A differential influence of temperature on insecticide toxicity between pests and their natural enemies may have important consequences on biological control in a global warming context. This study aimed to investigate cross effects between temperature and three insecticides-i.e., chlorantraniliprole, emamectin and spinosad-on the mortality of a major pest in orchards, Cydia pomonella L., and two of its natural enemies in southern France, the predatory earwig Forficula auricularia L. and the introduced parasitoid Mastrus ridens Horstmann. We observed a decreased efficiency of emamectin and spinosad with increasing temperature on mortality of codling moth, while no influence of temperature on chlorantraniliprole efficacy was observed. Increasing temperatures increased the toxicity of spinosad and chlorantraniliprole against M. ridens and only for emamectin on F. auricularia. This study provides essential insight to make recommendations for using these insecticides in combination with two natural enemies to control the codling moth in prevision of global warming. Our results suggest that the use of spinosad may become sub-optimal under higher temperatures. In contrast, chlorantraniliprole should be suitable under warmer climatic conditions to control C. pomonella and the less detrimental against F. auricularia and M. ridens. To conserve the use of biological control strategies relying on F. auricularia, alternating use of emamectin during early spring, when its toxicity is the lowest on this natural enemy, chlorantraniliprole during summer could limit resistance risks in codling moth populations and reduce the insecticides' impact on the populations of natural enemies