Biological control of Popillia japonica with an attract-and-infest strategy

Abstract: The Japanese beetle (Popillia japonica) is an invasive insect that is seriously
damaging agricultural production with its extremely polyphagous lifestyle. Only recently, the
pest has established in northern Italy and southern Switzerland and has been slowly but steadily expanding its range. To counteract this invasion, we aim to implement an attract-and-infest strategy, where we use adult beetles as vectors to disseminate a Swiss native strain of the fungal biocontrol agent Metarhizium brunneum in the adult and larval populations of the invasive pest. With lab and field experiments, we tested whether infested adults (1) carry the inoculum to the habitat of their offspring, thereby increasing first instar larval mortality, and (2) horizontally transmit the fungal inoculum to other adults. Lab results show that beetles can carry fungal inoculum to the soil and mortality of freshly hatched larvae is increased at high spore concentrations. However, increase in larval mortality could not be confirmed under semi-field conditions. This aligns with recent findings stating low susceptibility of Japanese beetle larvae to M. brunneum. However, lab and semi-field experiments demonstrated that inoculated beetles can indeed transmit the fungal spores horizontally and both donor and recipient beetles showed increased mortality. Thus, the fungal inoculum can be disseminated in the adult populations of the invasive insect pest. For further development of the strategy, we tested the persistence of the soil-borne entomopathogenic fungus under aboveground conditions and are currently building first prototypes of an attract-and-infest trap. With this approach, we aim to prevent or at least slow down the establishment of the Japanese beetle in currently non-infested areas in
northern Europe and to sustainably protect agricultural production.