Temporal and spatial variations in the parasitoid complex of the horse chestnut leafminer during its invasion of Europe

The enemy release hypothesis posits that the initial success of invasive species depends on the scarcity and poor adaptation of native natural enemies such as predators and parasitoids. As for parasitoids, invading hosts are first attacked at low rates by a species-poor complex of mainly generalist species. Over the years, however, parasitoid richness may increase either because the invading host continuously encounters new parasitoid species during its spread (geographic spread-hypothesis) or because local parasitoids need different periods of time to adapt to the novel host (adjustment-hypothesis). Both scenarios should result in a continuous increase of parasitoid richness over time. In this study, we reconstructed the development of the hymenopteran parasitoid complex of the invasive leafminer Cameraria ohridella (Lepidoptera, Gracillariidae). Our results show that the overall parasitism rate increases as a function of host residence time as well as geographic and climatic factors, altogether reflecting the historic spread of C. ohridella. The same variables also explain the individual parasitism rates of several species in the parasitoid complex, but fail to explain the abundance of others. Evidence supporting the “geographic spread-hypothesis” was found in the parasitism pattern of Cirrospilus talitzkii (Hymenoptera, Eulophidae), while that of Pediobius saulius, another eulophid, indicated an increase of parasitism rates by behavioral, phenological or biological adjustments. Compared to fully integrated host-parasitoid associations, however, parasitism rates of C. ohridella are still very low. In addition, the parasitoid complex lacks specialists, provided that the species determined are valid and not complexes of cryptic (and presumably more specialized) species. Probably, the adjustment of specialist parasitoids requires more than a few decades, particularly to invaders which establish in ecological niches free of native hosts, thus eliminating any possibility of recruitment of pre-adapted parasitoids

Temperature effects on “overwintering” phenology of a polyphagous, tropical fruit fly (Tephritidae) at the subtropical/temperate interface

Around the world, several pest tephritids are extending their ranges from warm tropical or Mediterranean climates into cooler temperate regions. The ability to tolerate climatic diversity is uncommon among insects, and understanding the population phenology drivers of such species across different parts of their range will be critical for their management. Here, we determined the role of temperature versus fruit availability on the population phenology of Queensland fruit fly, Bactrocera tryoni. Using a field site located at the subtropical/temperate interface, with host fruits continuously available, we monitored the development times and abundance of B. tryoni, a species which has invaded temperate Australia from the tropics. From fruit samples held at ambient and controlled conditions, the abundance of emerging flies was highly variable among collection dates, but the variance did not reflect the observed changes in temperature. For most samples, the survival rate of flies in a field site was lower than predicted by a day-degree population model fitted with mean daily field temperatures. The development time of the immature stage in the field was prolonged, presumably due to cooler ambient conditions, but the fitted day-degree population model consistently over-predicted estimated development times. Our results indicate that at the subtropical/temperate interface, the decline in B. tryoni populations during winter is only partly driven by temperature and host availability. We classify B. tryoni as a climate generalist, which likely employs physiological as well as behavioural mechanisms to achieve broad climatic tolerance ranges.</p

DROSKII: a transnational attempt for insight on the damage potential of Drosophila suzukii and on the development of risk management and control measures

“Droskii” is a 2-year project running in the frame of Euphresco II – an European Research Area Network (ERA-NET) project for the development and implementation of research policies in the field of statutory and emerging plant pests, diseases and invasive species – devoted to deepen the knowledge and to face the pressing needs posed by the recently introduced spotted wing drosophila (SWD), Drosophila suzukii (Matsumura) (Diptera: Drosophilidae). D. suzukii has a wide host range and can attack many fruit crops, mainly small fruits, fruit trees and grapevine. It poses a major challenge to the development of alternative Integrated Pest Management strategies. Given the importance of soft fruits, stone fruits and grapes in the daily food intake, the risk of pesticide residues from the over-reliance on chemical products, the main control measures currently adopted against D. suzukii, is increasing. Furthermore, the economic costs of SWD do not only include direct yield losses but also associated labour and material costs for monitoring and management as well as revenue losses due to the closure of fruit export markets from SWD-infested regions by trading partners. The “Droskii” project is sub-divided in four main work packages: 1) the monitoring and forecasting activities of D. suzukii in Europe, e.g. by means of the development of efficient traps; 2) evaluation of the susceptibility of different fruit varieties and host plants; 3) survey and assessment on the infestation of grapes varieties in Europe; 4) actions for the containment and control of D. suzukii by environmentally-friendly measures. An additional activity of this project will be the transnational dissemination of the project acquirements and the reduction of pesticide use in fruit production, a vital mission both for occupational health and for consumer safety