Biocontrol potential of insect soil assemblages associated with Popillia japonica in the Azorean crop fields

Abstract: Larval development of the Japanese Beetle Popillia japonica Newman, 1838
(Coleoptera, Rutelidae) occurs partially in the soil. This ecological characteristic places this
species in a very specialized habitat interacting with a wide diversity of soil inhabitants, which
also includes possible predators like predaceous insects, other invertebrate animals, and
microorganisms. Soil predators may play a role in controlling the populations of P. japonica,
but little is known about their impact and their diversity in the Azorean ecosystems. This work uncovers the possible role of these soil-inhabiting arthropods in the biological control of P. japonica in the crop ecosystems of the Azores.
This study collected 18,559 arthropod specimens from the phylum Arthropoda across four
classes, 12 orders, and 26 families in maize and pasture fields on the islands of São Miguel and São Jorge in the Azores. We identified 40 morphospecies, 38 at the species level and 2 at the family level. Our objective was to target the invasive pest Popillia japonica. We focused on four groups of generalist predators with omnivorous behavior: Opiliones (n = 4,270), Carabidae (n = 4,370), Staphylinidae (n = 1,697), and Anisolabididae (n = 885). These groups were selected based on their potential to predate on other live insect species and act as natural controllers, by reducing the densities and spread of the pest P. japonica.
The introduced Pseudoophonus rufipes and Pterostichus vernalis were the dominant
carabid taxa in maize and pasture fields, with higher abundances in the maize fields on São
Miguel Island. The dominant staphylinid taxon was Rugilus orbiculatus, which was more
abundant in maize fields on both islands. We assayed these most abundant arthropods and found that Calosoma olivieri and the introduced Pseudoophonus rufipes were found to be active predators of the P. japonica L3 larvae, revealing their potential as biological control agents for this invasive pest. Additionally, the introduced Euborellia annulipes demonstrated to be a voracious predator of P. japonica larvae. Currently, we are assaying the capacity of these predators to predate at different soil depths and using metabarcoding to explore their gut contents, accessing their diet diversity in Azorean crop soils during the phase of P. japonica reproduction.
In conclusion, this study provides valuable insights into the diversity and abundance of
arthropod communities in the Azores, focusing on potential biological control agents for the
invasive pest P. japonica.