ARS | Publication request: Ascorbic Acid Influences the Development and Immunocompetence of Larval Heliothis virescens

Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 20, 2009
Publication Date: September 8, 2009
Citation: Popham, H.J., Shelby, K. 2009. Ascorbic Acid Influences the Development and Immunocompetence of Larval Heliothis virescens. Entomologia Experimentalis et Applicata. 133:57-64.

Interpretive Summary: Insects, like humans, require specific nutrients to complete their development and maintain a healthy immune system. In this study, vitamin C (ascorbic acid) was examined for its importance in development and in supporting the immune system of the budworm, Heliothis virescens. Vitamin C was found necessary for healthy adult moths to develop. It was also found that the lower the amount of vitamin C fed to larvae, the more susceptible larvae were to a baculovirus. Larvae fed less vitamin C were also more infectious to a baculovirus when a virus producing a red fluorescent protein was employed to mark the movement of the virus. However, low levels of vitamin C did not change the levels of phenoloxidase, an enzyme that helps the immune system fight off attack, suggesting that vitamin C and phenoloxidase function separately. These findings help scientists understand which nutrients impact the development of different insects or groups of insects as well as the insect immune system. This information can be extrapolated to developmental data collected both in the field and in the laboratory when insects fed on plants or artificial diets containing different levels of vitamin C.

Technical Abstract: We report that ascorbic acid, which is known to be a free radical scavenger, to be important not only in insect development but also in larval resistance to baculovirus infection. We sequentially elevated the ascorbic acid content in diet and evaluated the effect on larval H. virescens development and immunocompetence. Ascorbic acid levels lower than 0.7 g/L slowed the growth rate of larvae, reduced pupal weights significantly, and severely inhibited adult emergence. Larvae developing on ascorbic acid deficient diet experienced far higher levels of mortality following per os infection. A viral dose causing 85% mortality in larvae reared on ascorbic acid-free diet caused 40% mortality in larvae fed diet supplemented with 2.4 g/L ascorbic acid. However, the virucidal activity in the hemolymph of 5th instar larvae did not decline with low levels of ascorbic acid. Viral infection in larvae fed an ascorbic acid-free diet, as monitored by epifluorescence microscopy, showed signs of infection much earlier than larvae fed control levels of ascorbic acid.