Onset of oviposition triggers abrupt reduction in migratory flight behavior and flight muscle in the female beet webworm, Loxostege sticticalis

Authors: CHENG, YUNXIA - Chinese Academy Of Agricultural Sciences; LUO, LIZHI - Chinese Academy Of Agricultural Sciences; Sappington, Thomas; JIANG, XINGFU - Chinese Academy Of Agricultural Sciences; ZHANG, LEI - Chinese Academy Of Agricultural Sciences; FROLOV, ANDREIN - All-Russian Institute For Plant Protection

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2016
Publication Date: 11/28/2016
Citation: Cheng, Y., Luo, L., Sappington, T.W., Jiang, X., Zhang, L., Frolov, A.N. 2016. Onset of oviposition triggers abrupt reduction in migratory flight behavior and flight muscle in the female beet webworm, Loxostege sticticalis. PLoS One. 11(11): e0166859. doi:10.1371/journal.pone.0166859.

Interpretive Summary: The beet webworm is a serious agricultural pest of several crops and pasture in Eurasia and North America. Like several other migratory pests of crops, it overwinters in southern regions and migrates north in the summer where outbreak populations can develop quickly in certain areas. In many migratory pests, reproduction and migratory flight behavior are negatively linked. Both are energetically expensive processes, and different species manage the costs in different ways by some sort of trade-off. In the beet webworm, migratory flight takes place mainly during the 5-6 days after emergence from the pupa but before egg-laying starts. To gain insight into how migratory flight and reproduction are coordinated in the female beet webworm, we conducted laboratory flight experiments beginning at the end of the pre-oviposition period. Our results indicate that onset of egg-laying triggers a decrease in flight performance and capacity in female beet webworms, as a way of actively managing reallocation of resources away from migratory flight and into egg production. In addition to the abrupt switch, there was a gradual decline in flight performance, flight muscle mass, and flight fuel relative to the number of eggs laid. Although the results show that substantial, albeit reduced, long-duration flights remain possible after egg-laying begins, additional long-distance migratory flights probably are not launched.

Technical Abstract: Flight and reproduction are usually considered as two life history traits that compete for resources in a migratory insect. The beet webworm, Loxostege sticticalis L., manages the costs of migratory flight and reproduction through a trade-off in timing of these two life history traits, where migratory behavior occurs during the preoviposition period. To gain insight into how migratory flight and reproduction are coordinated in the female beet webworm, we conducted experiments beginning at the end of the pre-oviposition period. We used flight mills to test whether flight performance and supportive flight musculature and fuel are affected by the number of eggs oviposited, or by the age of mated and unmated females after onset of oviposition by the former. The results showed that flight distance, flight velocity, flight duration, and flight muscle mass decreased abruptly at the onset of oviposition, compared to that of virgin females of the same age which did not change over the next 7 d. These results indicate that onset of oviposition triggers a decrease in flight performance and capacity in female beet webworms, as a way of actively managing reallocation of resources away from migratory flight and into egg production. In addition to the abrupt switch, there was a gradual, linear decline in flight performance, flight muscle mass, and flight fuel relative to the number of eggs oviposited. The histolysis of flight muscle and decrease of triglyceride content indicate a progressive degradation in the ability of adults to perform additional migratory flights after onset of oviposition. Although the results show that substantial, albeit reduced, long-duration flights remain possible after oviposition begins, additional long-distance migratory flights probably are not launched after the initiation of ovipostion.