Submitted to: Biocontrol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2008
Publication Date: 6/25/2008
Citation: Coudron, T.A., Shelby, K., Ellersieck, M.R., Odoom, E.D., Lim, E.E., Popham, H.J. 2008. Developmental response of Euplectrus comstockii (Hymenoptera: Eulophidae) to ascorbic acid in the diet of the larval host, Heliothis virescens (Lepidoptera: Noctuidae). Biocontrol. 54:175-182.
Interpretive Summary: The intensity of research and commercial efforts to improve the nutritional value in plants has the potential to benefit insects as well as humans and livestock, and by doing so could make it more difficult to control pest insects with biological control agents. Recent studies have shown that beneficial pathogens are less effective in controlling pest insects that feed on ascorbic acid-enhanced diets which were used to mimic a nutritionally enhanced plant. That finding demonstrates the need for more information on how nutritionally enhanced plants affect the relationship between beneficial insects and pest insects. In this study, a beneficial insect manifested improved biological traits when reared on a pest insect fed a diet enhanced with ascorbic acid. This discovery demonstrates that the most effective biological control agent in cropping systems comprised of nutritionally enhanced plants may prove to be the beneficial insect rather than the beneficial pathogen. Both researchers and commercial groups will find this information to be of considerable importance as they test ways to enhance a wide variety of nutritional substances in plants.
Technical Abstract: Recent developments in genetic engineering has paved the way for researchers to produce crops of high nutritional and yield value, in addition to being resistant to diseases and pests. Ascorbic acid is one of the nutrients that researchers are trying to enhance in plants. Studies have shown that the effectiveness of a baculovirus to control the insect pest, the budworm, Heliothis virescens, was inversely proportional to the concentration of ascorbic acid. This study investigated the effect of different levels of ascorbic acid in the diet of a beneficial wasp, Euplectrus comstockii, by measuring life history parameters of the wasp when reared on larvae fed a basal diet containing low and high levels of ascorbic acid. Data included oviposition, egg hatch, percent pupation, pupal weight, percent adult eclosion and the sex ratio. Analysis of variance (ANOVA) and odds ratio statistical analyzes were used to interpret the results. ANOVA showed that there was no significant effect of ascorbic acid on the number of eggs laid and on pupal weight. Odds and odds ratio analyses showed that the probability of egg hatch and adult emergence for the wasp increased with the amount of ascorbic acid in the diet of the budworm, and that the rate of development and probability of female or male progeny remained at 2:1 for most levels of ascorbic acid tested. Collectively, this would indicate that as the ascorbic acid concentration is increased in the pest insect (and perhaps as the ascorbic acid concentration in the plant is increased) the effectiveness of a baculovirus would decrease, but the effectiveness of the wasp is likely to increase.