Organic Pest Management: Strategies against the herbivorous true bugs Nezara viridula and Halyomorpha halys (Heteroptera: Pentatomidae)

Summary in the original language of the document

True bugs such as Nezara viridula and Halyomorpha halys (Heteroptera: Pentatomidae) have emerged as significant pests in Europe, with continuous warming trends expected to impact their ecology and distribution further, altering their economic significance. N. viridula and H. halys, both polyphagous pests, predominantly feed on pods, seeds, or fruits, synchronising their population peaks with the reproductive stages of their host species. Currently, there is a lack of developed products or officially recommended solutions against H. halys and N. viridula in Europe. Given the economic impact of invasive insects and the challenges posed by synthetic insecticides in farming, the focus shifted to sustainable pest management strategies. This master thesis investigates the post-spraying efficacy of entomopathogenic fungi Beauveria bassiana isolate GHA and calcium carbonate (CaCO3) against N. viridula and H. halys through a series of no-choice and two-choice experiments under laboratory conditions. The no-choice experiment assessed the impact of B. bassiana treatment on mortality and developmental aspects (specifically body weight) of the N. viridula. In comparison, the two-choice experiment focused on assessing the repellent effect of CaCO3 on N. viridula and H. halys nymphs. In this study, true bug nymphs were exposed to bean plants (Phaseolus vulgaris) sprayed with plant protection agents. Contrary to expectations, the results from the no-choice experiments revealed that B. bassiana treatment neither caused mortality nor affected the development of N. viridula nymphs within the timeframe of three weeks. Moreover, the main and control treatments demonstrated no differences in group weight measurements of N. viridula nymphs. The absence of lethal and sublethal effects prompts an investigation into potential impacts on feeding behaviour, reproductive capacity, and long-term survival. Due to the insufficient number of H. halys nymphs available, the present study could not conduct a no-choice experiment. This highlights the need for additional research to confirm the effectiveness of B. bassiana as a control agent for H. halys. Subsequent two-choice experiments examined the impact of CaCO3-treated bean plants on the behaviour of N. viridula and H. halys. Both insect species exhibited minimal activity during the initial time intervals (0.5 and 1 hour), with most nymphs observed on bean plants after 24 hours. Surprisingly, neither species avoided bean plants treated with the test substance, challenging the hypothesis that CaCO3 treatment would deter feeding and induce avoidance behaviour in true bug nymphs. Based on these findings, CaCO3 proved to be ineffective in deterring the studied true bugs. To enhance future studies, it would be advantageous to record insect movements after a delay of at least 1 hour, as nymphs may not be fully prepared to make choices at the beginning of the experiment. It is also recommended to explore other potential repellents that could be part of true bugs management using sustainable measures. Thus, research efforts are needed to identify active ingredients compatible with organic and integrated pest management approaches against polyphagous true bugs N. viridula and H. halys.