Impact of Nosema maddoxi and Colletotrichum fioriniae on brown marmorated stink bugs

The microsporidian Nosema maddoxi was described from brown marmorated stink bugs (Halyomorpha halys; BMSB) in 2017. It has been found infecting BMSB in the eastern and western US and in West Georgia (Caucasus). Nosema maddoxi is transmitted both horizontally and vertically. Lab bioassays demonstrated that infection of adult BMSB shortened lives and reduced female fecundity. Some studies in the US and Georgia reported the highest infection levels in spring, after adults overwintered. Studies focusing on overwintering demonstrated that 13% of survivors were infected with N. maddoxi while 33% of those moribund or dead were infected with N. maddoxi. Another pathogen, Colletotrichum fioriniae, not previously reported from BMSB, was found infecting almost 50% of moribund or dead overwintering BMSB, co-occurring with N. maddoxi in 11% of BMSB that died while overwintering. Koch’s postulates proved that C. fioriniae is pathogenic to BMSB, although this fungus is also known as a plant pathogen and endophyte. However, C. fioriniae infections were not found in living BMSB when overwintering shelters were sampled and only occurred at low levels post-overwintering. Horizontal transmission of N. maddoxi occurs readily among caged BMSB, causing problems when BMSB colonies are needed for parasitoid production. On the other hand, habitat suitability models investigating current and future (2070) climates, have shown that BMSB and N. maddoxi have broad similarities in habitat suitability. Biological control provided by N. maddoxi could be key for managing BMSB in the future.