Microhymenoptera are tiny, parasitoid wasps that develop in or on other insects. As they grow, they kill their hosts and thus greatly contribute to maintaining the natural balance by regulating the populations of their hosts. Despite their enormous biodiversity and essential function in various ecosystems, Microhymenoptera are often ‘overlooked’ in scientific studies, insect monitorings and conservation programmes. This is not only due to the small size of the ‘mini wasps’, but also because of the demanding identification and lack of wasp experts.
Maura Haas-Renninger from the Stuttgart Natural History Museum and her team have now investigated whether measuring the general insect biomass of a habitat allows inferences about the quantity and diversity of the microhymenoptera living there and how severely they are affected by the general decline in insects.
For their study, they analysed insect samples obtained from three Malaise traps, which are being used in another long-term study by the Stuttgart Natural History Museum to monitor the biomass of flying insects in south-west Germany. Between March and November 2019, they regularly removed the insects and counted the microhymenoptera they contained.
The experiment not only enabled the research team to gain an overview of the number and diversity of this group of animals, but also to observe the phenology, i.e. the seasonal occurrence of different Microhymenoptera species over the course of a year. Most species of the parasitoid wasps studied reach their peak abundance between June and July and between July and August.
The results show that measuring the general insect biomass (at least on the grasslands of south-west Germany) is a good indicator for tracking changes in the abundance and diversity of even the smallest parasitoid wasps. However, this also means that the Microhymenoptera are at least as strongly affected by insect decline as their larger and much better known relatives.
Overall, this study provides an important initial basis for easily recording the extent of diversity of this ecologically extremely important group of insects. In addition, the results of this study can contribute to the protection of Microhymenoptera, for example by adjusting the timing of mowing in meadows and pastures to the phenology of the wasps.
The article was published in the scientific journal “Journal of Hymenoptera Research”.