ARS | Publication request: Synchronized oviposition triggered by migratory flight intensifies larval outbreaks of beet webworm

Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 13, 2012
Publication Date: February 9, 2012
Citation: Cheng, Y., Luo, L., Jiang, X., Sappington, T.W. 2012. Synchronized oviposition triggered by migratory flight intensifies larval outbreaks of beet webworm. PLoS One. 7(2):e31562.

Interpretive Summary: The beet webworm is a serious agricultural pest of several crops and pasture in Asia. It overwinters as a full grown caterpillar in southern regions and escapes summer heat by migrating north. Many crop pests in North America use the same strategy, and their place and time of arrival in the north are difficult to predict. In laboratory experiments using flight mills, we found that moths probably do not begin migration until the second day of adulthood, and that there is no measurable decrease in lifetime eggs laid despite all the energy needed for long-duration flight. However, egg-laying by females following a migratory flight tends to be more synchronized as a group, and happens over a shorter time. It is likely that this contributes to high larval densities and severity of outbreaks in northern areas that receive the migrants. This information will be used by university and government scientists in China, the U.S., and elsewhere around the globe to better understand the relationship between hibernation, reproductive potential, and migration by these and related migratory pests. The more we learn about such pests and their biology, the better we can warn farmers of infestations and protect the crops they attack.

Technical Abstract: The beet webworm (BWW), Loxostege sticticalis L. (Lepidoptera: Pyralidae), a migrant species surviving in the belt zone of 36-54 degrees N, is one of the most destructive insect pests of crops and fodder plants in northern China. Flight capacity, preoviposition period (POP), period of first oviposition (PFO), mating capacity, lifetime fecundity, and other related traits in adult BWW flown on flight mills for 12 h at days 1, 2, 3, and 5, and for 12, 18, and 24 h at d3 of the adult life were investigated to determine the potential migratory ages at which reproductive costs are minimal, and to characterize variation in reproductive output and behavior after flight. Results showed that the 1-d-old adults flew relatively less, but their POP and PFO were significantly prolonged, and lifetime fecundity decreased after flight compared to unflown controls. These traits in the moths flown at d2, d3, and d5 of adult life differed greatly, with no observed reproductive costs despite greater flight activity. We conclude that the BWW probably does not start migration until the 2nd night after emergence to avoid the reproductive costs. Regardless, lifetime fecundity, mating percentage and frequency, longevity, and egg hatching rate for adults that experienced various flight tests did not differ significantly from unflown moths, suggesting there are no reproductive costs associated with migration in BWW. Finally, PFO and oviposition period of the moths flown at d3 and d5, and flown for more than 12 h at 3d were shorter than that of the unflown moths. This suggests that oviposition by L. sticticalis adults after a migratory flight is more synchronous and fast, which may contribute to high larval densities and result in outbreak populations.