Jeannine Pizzol

Biological invasion of European tomato crops by Tuta absoluta: ecology, geographic expansion and prospects for biological control.

The tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is a devastating pest of tomato originating from South America. After its initial detection in eastern Spain in 2006, it rapidly invaded various other European countries and spread throughout the Mediterranean basin. If no control measures are taken, then the pest can cause up to 80–100% yield losses in tomato crops in recently invaded areas and may pose a threat to both greenhouse and open-field tomato production. The exceptional speed and extent of T. absoluta invasion have called for studies documenting its biology and ecology, while indicating an urgent need for efficient and sustainable management methods. The development of approaches to manage T. absoluta would be facilitated through a detailed revision of information on this pest in its area of origin. This review combines information on the invasion by T. absoluta, its ecology, and potential management strategies, including data that may help the implementation of efficient biological control programs. These programs, together with a variety of other management tactics, may allow efficient integrated pest management of T. absoluta in Europe and Mediterranean Basin countries.

Temperature-dependent differences in biological traits between two strains of Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae)

Parasitoids’ efficiency in controlling pests depends not only on their ability to parasitize their hosts but also on how much they are adapted to climatic conditions (notably temperature) of the area where they are planned to be released. In addition, the optimal conditions for production of parasitoids used for inundative releases like Trichogramma spp. may also vary largely as a function of strains. Using the parasitoid Trichogramma cacoeciae Marchal as biological model, we studied how temperature affects important parasitoid efficiency-related biological traits under laboratory conditions. Emergence, mortality rates and fecundity of two strains of T. cacoeciae, one originating from France (Alsace) and the other one from Tunisia (Degache), were compared at constant temperatures of 15, 20, 25 and 30°C. The parasitoids of the French strain showed highest fecundity at 25°C with wasps that had been reared at 20 or 25°C. The Tunisian strain showed the highest fecundity at 25°C, but only when wasps were previously reared at 25 or 30°C. For both strains, the highest mortality occurred among wasps that had laid eggs at 30°C. Emergence rates were relatively high at all temperatures, although the French strain did better at 15–25°C and the Tunisian one at 20–30°C. Because of the differences in biological traits of these two T.cacoeciae strains in relation to the temperature, a judicious choice must be made among the various strains when using this species in biological control programs.

Genetic variation in progeny allocation in Trichogramma maidis

A considerable amount of work has been recently devoted to the study of progeny allocation strategies by insect parasitoids under different environmental constraints (see Waage, 1986, for a review). All these studies present each of the oviposition strategies (e.g. number of eggs laid per host, superparasitism) as a phenomenon which is progressively settled by natural selection during the course of generations. However, this optimal progeny allocation theory is conceivable only if the variation in wasps biological traits involved are under a genetic control on which natural selection could act. We have decided therefore to look for a genetic variability in these traits in a Trichogramma maidis Pintureau & Voegelé (Hym.; Trichogrammatidae) population.

Effect of photoperiod experienced by parents on diapause induction in Trichogramma cacoeciae

In the genus Trichogramma, the prepupal stage can survive the cold season in diapause. However, optimal conditions for the induction of this cessation of development during the process of mass production of the parasitoid in a biological control program depend on the species. In Trichogramma cacoeciae Marchal (Hymenoptera: Trichogrammatidae), diapause is induced more easily if the parents are reared under short‐day conditions (L10:D14), and if the temperature is 10 °C rather than 13 °C. However, the effect of parental photoperiod on diapause induction is weaker at lower temperatures (10 °C). Following diapause induction, individuals can be stored at 3 °C for several months, up to 1 year. Non‐optimal conditions led to the establishment of a quiescent state in some or all individuals. In such cases, it was necessary to reduce the storage period to 1 or 2 months only, to prevent high mortality rates and low fecundity.

Effects of endosymbiotic Wolbachia on the diapause in Trichogramma hosts and effects of the diapause on Wolbachia

Abstract Used as an agent in biological control, Trichogramma which has been infected by endosymbiotic bacteria belonging to the genus Wolbachia and inducing the thelytokous mode of reproduction, increases rearing productivity in commercial insectaries. These insectaries can now make use of Trichogramma diapause to spread out and optimise their production. We therefore studied the effect of Wolbachia on the diapause in Trichogramma evanescens. The symbionts show no beneficial or harmful effect on the proportion of emergence in diapausing individuals or on their fecundity. Therefore, infected strains can easily be used in crop protection. On the other hand, low temperatures exert a slightly negative effect on Wolbachia, as detected from the proportion of females in the offspring of symbiotic diapausing females.

Within-Crop Air Temperature and Humidity Outcomes on Spatio-Temporal Distribution of the Key Rose Pest Frankliniella occidentalis

Frankliniella occidentalis (Pergande) is a key pest of various crops worldwide. In this study, we analyse the dependence of the infestation of this pest on spatially distributed micro climatic factors in a rose greenhouse. Despite the importance of this subject, the few existing studies have been realized in laboratory rather than in greenhouse conditions. However, recent progress on greenhouse microclimate characterisation has highlighted the strong indoor climate heterogeneity that may influence the within-crop pest distribution. In this study, both microclimate (air temperature and humidity) and thrips distribution were simultaneously mapped in a rose greenhouse. The measurements were sensed in a horizontal plane situated at mid-height of the rose crop inside the greenhouse. Simultaneously, thrips population dynamics were assessed after an artificial and homogeneous infestation of the rose crop. The spatio-temporal distribution of climate and thrips within the greenhouse were compared, and links between thrips infestation and climatic conditions were investigated. A statistical model was used to define the favourable climate conditions for thrips adults and larvae. Our results showed that (i) the air temperature and air humidity were very heterogeneously distributed within the crop, (ii) pest populations aggregated in the most favourable climatic areas and (iii) the highest population density of thrips adults and larvae were recorded at 27°C and 22°C for temperature and 63% and 86% for humidity, respectively. These findings confirm, in real rose cropping conditions, previous laboratory studies on the F. occidentalis climatic optimum and provide a solid scientific support for climatic-based control methods against this pest.