Gebruik van entomopathogene schimmels en eiparasitoïden om de biologische controle van Nezara viridula in een vroeg stadium te verbeteren

To feed a growing global population while minimising environmental harm, it is essential to increase crop yields and reduce crop losses. Arthropods alone are responsible for approximately one-fourth of global crop losses, amounting over €450 billion annually, and climate change is expected to worsen their impact by enhancing pest insect survival, reproduction and distribution. For centuries, pest management has primarily relied on chemical pesticides. However, these chemicals pose significant environmental risks, harm non-target organisms and contribute to the development of pesticide resistance in pest populations. As a result, the EU is progressively phasing out chemical pesticides in favour of more sustainable approaches like Integrated Pest Management (IPM) and biological control. Biocontrol agents, including arthropod predators, parasitoids (i.e. insects that lay their eggs inside or onto other insects), entomopathogenic microbes and plant-derived substances, offer targeted pest control with fewer ecological drawbacks. While biological control strategies targeting nymphal and adult insect stages have seen substantial progress, early-life-stage control, particularly at the egg stage, has received less attention. Targeting pest eggs can prevent crop damage before it begins, making egg-killing agents such as entomopathogenic fungi and egg parasitoids promising candidates for effective biocontrol. However, challenges remain in improving the longevity and host-finding efficiency of egg parasitoids, which are critical for maximising their effectiveness. The main objectives of this PhD study were to assess the potential of entomopathogenic fungi for killing insect eggs and to examine how the performance of egg parasitoids can be improved, focusing on sugar provisioning and the effects of egg deposition on the olfactory behaviour of egg parasitoids. Additionally, a thorough investigation of the egg microbiome was undertaken, along with a preliminary study on the role of egg-associated bacteria as potential cues for host recognition by egg parasitoids. To address these research objectives, sweet pepper (Capsicum annuum L., Solanaceae), the invasive Southern green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae), and its main egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) were used as study system. Nezara viridula is a polyphagous pest species originating from Ethiopia, which commonly occurs in Mediterranean and (sub)tropical regions. Due to global warming and human activity, it has recently expanded its range to Northwestern Europe, including Belgium and the Netherlands, where it causes significant economic damage to greenhouse crops like sweet pepper, cucumber, and eggplant. Until recently, control of N. viridula relied heavily on chemical insecticides, posing a major challenge to the implementation of IPM programs. More recently, the egg parasitoid T. basalis has been introduced to control the pest in greenhouse horticulture. This parasitoid is regarded as one of the most important natural enemies of N. viridula worldwide and is a key biocontrol agent against pentatomid bug species, especially because of its high parasitism efficiency. However, there is still room for improvement in its efficacy, particularly because the production costs for egg parasitoids like T. basalis are high and repeated releases are necessary to achieve effective pest suppression.