Abstract
In a context of globalization and climate change, more and more insects are becoming invasive, particularly affecting agriculture on a global scale. At the heart of this network of invasions, the United States of America is experiencing the arrival of many species, mainly from Asia. Among them, stink bugs (Pentatomidae) threaten most American agrosystems and are now mainly regulated by synthetic pesticides. Bagrada hilaris (bagrada), native to Asia and Africa, is the most recent species to invade the USA, where it has been reported since 2008 in Brassicaceae crops. To answer the needs of farmers, USDA-ARS funded a classical biological control program to select and introduce from its native range one or more natural enemies of bagrada into California. The research included in this PhD thesis is part of this program. It sought to assess in a quarantine greenhouse whether the oophagous parasitoid Gryon gonikopalense (Scelionidae), native to Pakistan, could establish in California and efficiently control bagrada. Thus, four main objectives were defined: 1) to describe the general biology of G. gonikopalense; 2) describe its host foraging behavior; 3) examine the possibility of its mass production and 4) assess its specificity towards bagrada using Euro-Mediterranean non-target stink bugs. Objective 1 allowed to show that the physiology of G. gonikopalense was similar to that of many other scelionids: depending on the temperature, it completed its development in 7 to 25 days, its lifespan ranges from 30 to 150 days and it is able to parasitize hundred eggs during its lifetime. It shares with bagrada a thermal optimum between 25 and 35 °C which could allow it to settle in California. In addition to being an effective parasitoid of bagrada, the advantage of G. gonikopalense particularly involves its foraging behavior for host's eggs, which are buried in the ground in 90% of cases. We found that G. gonikopalense was able to dig into the soil to parasitize eggs. In addition, we have shown in a tri-trophic system that the parasitoid mainly attacks the buried eggs of bagrada, while being able to reach the eggs deposited on the host plant (about 10%). For the 3rd objective, we have shown that the storage of bagrada eggs at 5 °C over three weeks made it possible to optimize the breeding of the parasitoid and facilitate mass production. Concerning the objective 4, still in progress, we showed that among the 11 pentatomids tested, at least four were suitable for the parasitoid, and two of them were mainly located around the Mediterranean basin. These results complement the tests carried out in California and open a proactive discussion on the introduction of G. gonikopalense in invasive Mediterranean populations of bagrada. Finally, during this thesis, we have described several aspects, hitherto unknown, of the biology of G. gonikopalense. Its behavioral specialization towards bagrada makes this parasitoid particularly promising for the biological control program. A petition-to-release drafted on the basis of this knowledge submitted to the health authorities of the USA remains a short-term objective. They will then assess the risks and benefits of using G. gonikopalense to control bagrada in California.