A mite parasitoid, Pyemotes zhonghuajia, negatively impacts the fitness traits and immune response of the fall armyworm, Spodoptera frugiperda

Parasitoids are key regulators in ecological communities and widely used as agents in biocontrol programmes. The fall armyworm, Spodoptera frugiperda, recently invaded multiple continents and caused substantial economic losses in agriculture. Pyemotes zhonghuajia, a newly identified mite parasitoid, has shown potential for controlling various agricultural insect pests. Therefore, this study tested the performance of P. zhonghuajia in parasitising S. frugiperda. We also investigated the sublethal effects of parasitism by P. zhonghuajia on host fitness traits, transgenerational impacts, and cellular and humoral immunity. Our result showed that the fifth-instar larvae of S. frugiperda parasitised by 40 P. zhonghuajia were all dead (i.e., a lethal effect), while parasitism by 5 or 10 P. zhonghuajia was considered sublethal since many S. frugiperda survived to adulthood and produced offspring after mating. The sublethal influences from parasitism by P. zhonghuajia resulted in reduced pupal weight, adult emergence rate and fecundity, but increased developmental time and longevity. Parasitism at both lethal (40 mites) and sublethal (10 mites) levels impaired the cellular and humoral immunity of S. frugiperda. This study presents the first empirical evidence that mite parasitoids can negatively influence host immunity. Moreover, it provides insights into the biocontrol potential of mite parasitoids and their interactions with hosts.