Prostaglandin‐mediated recovery from bacteremia delays larval development in fall armyworm, Spodoptera frugiperda

Abstract

Insect immunity includes a surveillance system that detects and signals infections, coupled with hemocytic and humoral immune functions. These functions are signaled and coordinated by several biochemicals, including biogenic amines, insect cytokines, peptides, and prostaglandins (PGs). The actions of these mediators are coordinated within cells by various forms of cross-talk among the signaling systems and they result in effective reactions to infection. While this is well understood, we lack information on how immune-mediated recovery influences subsequent juvenile development in surviving insects. We investigated this point by posing the hypothesis that PG signaling is necessary for larval recovery, although the recovery imposes biological costs, registered in developmental delays and failures in surviving individuals. Here, we report that nodulation responses to infections by the bacterium, Serratia marcescens, increased over time up to 5 h postinfection, with no further nodulation; it increased in a linear manner with increasing bacterial dosages. Larval survivorship decreased with increasing bacterial doses. Treating larvae with the PG-biosynthesis inhibitor, indomethacin, led to sharply decreased nodulation reactions to infection, which were rescued in larvae cotreated with indomethacin and the PG-precursor, arachidonic acid. Although nodulation was fully rescued, all bacterial challenged larvae suffered reduced survivorship compared to controls. Bacterial infection led to reduced developmental rates in larvae, but not pupae. Adult emergence from pupae that developed from experimental larvae was also decreased. Taken together, our data potently bolster our hypothesis.

The Galleria mellonella-Enteropathogenic Escherichia coli Model System: Characterization of Pathogen Virulence and Insect Immune Responses

“…It was hypothesized to enhance immune responses in diseased insects since reduced lipid intake decreases hemolymph lipid concentration, which increases available apolipophorin III for pathogen recognition ( Adamo et al 2010 ). In general, these results were consistent with a recent study, in which the recovery from Serratia marcescens infection increased larval development time, decreased pupal mass, and decreased adult eclosion rate in Spodoptera frugiperda ( Zhang et al 2018 ). Thus, growth inhibition may be a common sublethal effect of bacterial infections in lepidopteran insects.…”

Overexpression of PGE2 synthase by in vivo transient expression enhances immunocompetency along with fitness cost in a lepidopteran insect

“…Yajima et al (2003) showed that the PLA 2 activity is associated with IMD immune signaling to produce AMPs in Drosophila. Furthermore, Zhang et al (2018) showed that PGs rescued Spodoptera frugiperda larvae infected with an entomopathogen, Serratia marcescens.…”

“…In the honey bee, immune challenge reduces expression and accumulation of stored plasma proteins such as vitellogenin and hexamerin, whereas it highly induces immune-associated genes, defensin and prophenoloxidase, suggesting an adaptive strategy to redirect resources to combat injury or infection (Lourenço et al, 2009). In S. frugiperda, in which PGs played a crucial role in mediating cellular immune response, the PG-treated larvae suffered reduced survivorship compared with controls (Zhang et al, 2018), indicating a fitness cost. Thus, PGE 2 is crucial for S. exigua survivability, but the excessive amount may impose to reduced pupal mass and adult fecundity owing to a trade-off effect.…”

Trade-Offs among Immune Mechanisms: Bacterial-Challenged Spodoptera frugiperda Larvae Reduce Nodulation Reactions during Behavioral Fever

“…Unlike other insect species, in which nodules are similar in size and can be directly counted [4], the nodules in fall armyworms are highly variable in size. To record nodules for this paper, we counted Indexed Nodules (IN) following the method of Zhang et al [20]. In detail, we recorded the diameters of each nodule, which occurred in a size range of about 20 to over 200 µm.…”