D3220: The effect of flight on susceptibility to pathogens in the desert locust, Schistocerca gregaria

Locusts are grasshoppers that exhibit density-dependent phase-dependent polyphenism and can migrate long distances in massive groups causing devastating impacts on agriculture. While their powerful flight helps them find resources, it may also make them susceptible to pathogens. During flight, adipokinetic hormone (AKH) is released by corpora cardiaca of the locust which causes lipid mobilization from the fat body to the flight muscles via hemolymph to fuel energetically costly migration. It has previously been shown that injections of AKH increase mortality of locusts following an immune challenge, possibly because a lipid-rich hemolymph provides a conducive environment for pathogens to thrive. We will directly test how flight affects locust responses to the fungal biopesticide Metarhizium. We hypothesize that flight increases lipid levels in the hemolymph, enhancing growth of Metarhizium, leading to increased locust mortality. We further hypothesize that infected and flying locusts will produce a stronger immune response but that it will not be sufficient to stave off the pathogen. To test these hypotheses, we will use a full factorial design with locusts either flown or not, and infected or not, and measure locust survival, in vivo fungal growth, hemocyte count, phenoloxidase activity, and hemolymph lipid content. To test whether increased lipid content speeds growth of the fungal pathogen, we will manipulate lipid contents for in vitro cultures of Metarhizium and quantify growth. Overall, this experiment will provide a better understanding of the potential trade ofs between migration and immune function in migratory locusts. This work was supported by NSF DBI 2021795.