Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2007
Publication Date: 6/1/2007
Citation: Shelby, K., Popham, H.J. 2007. Plasma selenium levels correlate with elevated immunocompetence of Heliothis virescens larvae against baculovirus infection. Journal of Invertebrate Pathology. 95(2):77-83. Interpretive Summary: When insects feed on plants they encounter many nutrients, such as selenium, that aid the insect in staying healthy. Specifically, these nutrients assist the insect when combating toxic plant chemicals and attacks from other insects and microbials. However, the details of how these nutrients impact the physiology of an insect and further, how these nutrients aid the insects when responding to a viral infection is virtually unknown. In an effort to determine whether larvae accumulated selenium in their tissues and if this would bolster their ability to fight off an insect virus infection, we fed varying doses of selenium to budworm caterpillars, a pest of corn and soybeans, and then measured the response of the insect to infection with a virus. Selenium in general caused larvae to grow more slowly as the amount they were fed increased but it also increased the ability of larvae to fight off viral infection. This finding helps scientists understand that plant and soil types impact the results of biological control in the field. It also helps scientists understand how what they feed insects impacts their experimental results.
Technical Abstract: We have previously found that dietary Sodium Selenium (Se) impacted the growth and development of Trichoplusia ni reared for many generations on diet containing extremely low levels of Se. Larvae had an elevated resistance to per os infection with a baculovirus. In this study we examine how dietary Se affects the growth, development, and Se content of Heliothis virescens that have been laboratory reared for less than two years. Larvae fed a commercial tobacco budworm diet supplemented with greater than 10 ppm Se grew at a slower rate than insects fed lower levels of selenium and had an increase in the amount of Se sequestered in pupae. Larvae fed diets containing from 5-25 ppm Se exhibited elevated plasma concentrations of the micronutrient and an increase in the plasma virucidal activity against a baculovirus using an in vitro assay. Larvae were reared on diet supplemented with 5 or 25 ppm Se until the onset of the penultimate instar then infected per os or by injection with increasing concentrations of the fatal baculovirus Autographa californica multiple nucleopolyhedrovirus. Larvae fed 25 ppm and infected with occluded virus per os were more resistant to viral infection than infected larvae not fed Se. Larvae injected with budded virus were more resistant when they had been fed 5 ppm Se than those that had been reared on diet containing 0 or 25 ppm Se.