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

Authors: ZHANG, LEI - Chinese Academy Of Agricultural Sciences; Ringbauer, Joseph - Joe; Goodman, Cynthia; Reall, Tamra; JIANG, XING-FU - Chinese Academy Of Agricultural Sciences; Stanley, David

Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2017
Publication Date: 1/29/2018
Citation: Zhang, L., Ringbauer Jr, J.A., Goodman, C.L., Reall, T., Jiang, X., Stanley, D.W. 2018. Prostaglandin-mediated recovery from bacteremia delays larval development in fall armyworm, Spodoptera frugiperda. Archives of Insect Biochemistry and Physiology. https://doi.org/10.1002/arch.21444.
DOI: https://doi.org/10.1002/arch.21444

Interpretive Summary: Chemical insecticides are effective pest insect management tools, however, negative effects, including environmental contamination and insect resistance to the insecticides attend use of these products. These negative effects drive research into alternative insect management technologies such as microbial biological control and tools to disable insect immune reactions to infection. Progress toward this goal is hindered because we lack information on how immune-mediated recovery influences subsequent juvenile development in surviving insects. We investigated this point in fall armyworms by posing the hypothesis that immune signaling is necessary for larval recovery, although the recovery imposes biological costs. Here, we report that immune responses to bacterial infection increased over time after infection and increased with increasing bacterial dosages. We found that all bacterial-challenged armyworms were able to fully recover from modest infections, however, armyworm development was delayed and adult emergence was decreased. Our data support our hypothesis. These findings will be used by scientists researching microbial biocontrol and ultimately used to improve global food security by developing alternatives to classical chemical pest control measures.

Technical 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 post-infection up to 5 h PI, 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 co-treated with indomethacin and the PG-precursor AA. 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.