Submitted to: Journal of Applied Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/2/2010
Publication Date: 2/1/2011
Citation: Dorhout, D.L., Sappington, T.W., Lewis, L.C., Rice, M.E. 2011. Flight behavior of European corn borer infected with Nosema pyrausta. Journal of Applied Entomology. 135(1-2):25-37. Interpretive Summary: The European corn borer is a major insect pest of corn in the U.S. Recent research has demonstrated the importance of long-distance movement of this moth to its population dynamics and to the effectiveness of current insect resistance management strategies being used to slow development of resistance to transgenic Bacillus thuringiensis (Bt)-corn that farmers plant to kill the larvae. A pathogen, Nosema pyrausta, is a common disease of European corn borers that reduces longevity and the number of lifetime eggs laid by the moths. We used laboratory flight mills to test the effects of Nosema infection on flight behavior of European corn borer moths of different sexes and ages. Nosema does have a negative effect on measures of flight distance, duration, and speed, especially in males, with effects in females detected only when infection was at a moderate to heavy level, as measured by spore counts in adult tissue. Forewing length, an index of overall body size, was positively related to flight performance, especially in males, and especially when the moths were infected with Nosema. Males and females that were infected with Nosema weighed less than those that were healthy, but infection was not related to length of the forewing. Thus, it is likely that the negative effects of Nosema infection on flight activity are due to reduction in fuel reserves needed to support flight rather than to effects on wing length. Our results will be used by university and government scientists trying to understand and model European corn borer population dynamics, as well as potential development and spread of resistance to transgenic Bt-corn in the presence of natural Nosema infections.
Technical Abstract: The microsporidian Nosema pyrausta is a common and widespread pathogen of European corn borer, Ostrinia nubilalis (Hubner), in North America and Europe. Nosema negatively affects European corn borer longevity and fecundity. In this study, we used flight mills to examine the effects of Nosema infection on flight activity of unmated males and females at 1 and 3 days after eclosion from the pupa, taking level of infection, as measured by number of Nosema spores/mg of tissue, into consideration. Nosema infection had a significant negative effect on distance, duration, and speed of the longest uninterrupted flight, as well as on total distance and duration of flight of 1-d-old males, but not of 3-d-old males or females of either age. However, when insects with a light infection (< 15 spores/mg) were pooled with uninfected moths, significant negative effects of a moderate/heavy infection (> 15 spores/mg) were observed for most flight parameters in all but 3-d-old females. The magnitude of reduction was often substantial, e.g., distance and duration were 7-fold, and 3.5-fold less, respectively, in 1-d-old females with a moderate/heavy infection. Flight distance and duration were significantly negatively correlated with level of Nosema infection in 1-d-old, but not 3-d-old, moths of both sexes. The percentage of moths of either sex or age with a moderate/heavy Nosema infection flying given distances was less than that of lightly-infected (< 15 spores/mg) moths. Among uninfected adults, forewing length was positively correlated with several measures of flight performance in males, but not females. However, some performance measures were correlated with wing length in females when infected with Nosema. Nosema infection was associated with reduced adult weight, but not forewing length, suggesting that negative effects of Nosema infection on flight performance are related to reduced energy reserves rather than shorter wings.