Starvation on first or second day of adulthood reverses larval-stage decision to migrate in beet webworm (Lepidoptera: Pyralidae)

Authors: CHENG, YUNXIA - Chinese Academy Of Agricultural Sciences; Sappington, Thomas; LUO, LIZHI - Chinese Academy Of Agricultural Sciences; ZHANG, LEI - Chinese Academy Of Agricultural Sciences; JIANG, XINGFU - Chinese Academy Of Agricultural Sciences

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2021
Publication Date: 3/10/2021
Citation: Cheng, Y., Sappington, T.W., Luo, L., Zhang, L., Jiang, X. 2021. Starvation on first or second day of adulthood reverses larval-stage decision to migrate in beet webworm (Lepidoptera: Pyralidae). Environmental Entomology. 50(3):523-531. https://doi.org/10.1093/ee/nvab015.
DOI: https://doi.org/10.1093/ee/nvab015

Interpretive Summary: The beet webworm is a serious agricultural insect pest of several crops and pasture in Eurasia and North America. It overwinters in southern regions and migrates north in the summer where outbreak populations can develop quickly in certain areas. However, the decision to migrate as an adult or reproduce locally is made in the larval stage depending on environmental conditions like crowding experienced by the larva. We recently discovered in two other migratory moth species that a larval decision to migrate can be reversed in the adult stage if an environmental stress is encountered soon after emergence from the pupa. Our goal in this study was to determine if this phenomenon is present in this species also, and if so, to define the sensitive period. In many migratory moths, including the beet webworm, reproduction and migratory flight behavior are negatively linked. Both are energetically expensive processes, and different species manage the costs in different ways by developmental trade-offs. In the beet webworm, migratory flight takes place mainly during the 5-6 days after emergence from the pupa but before egg-development and laying starts. We put stress on the adults by starving them for different periods and durations after emergence, then monitored timing of reproductive development, growth of flight muscles, and flight performance in laboratory tethered-flight experiments. The results indicate that the first two days of adult life in the beet webworm is the sensitive stage during which presumed migrants can be switched to residents by an appropriate environmental cue. Whether applied during or outside the sensitive stage, starvation did not influence lifetime egg production, the number of days over which eggs were laid, life span, or the proportion of eggs that hatch after being laid by the starvation-stressed moths. This information provides valuable insight into the dynamics controlling migration behavior of pest moths, and will be applicable to closely related migratory corn pests like European corn borer in North America.

Technical Abstract: A facultative commitment to adult migration in the larval stage can be modified again after adult emergence in some Lepidoptera when influenced by an appropriate environmental cue during a sensitive stage. This phenomenon is termed secondary regulation of migration. The sensitive stage in adult beet webworm, Loxostege sticticalis, was determined experimentally by starvation of presumed migrant females reared from gregarious-phase larvae. When presumed migrant adults were starved for 24 h on either of the first two days after emergence, the pre-oviposition period was shortened. In contrast, pre-oviposition periods were not significantly shortened for migrants starved on day 3 or when starvation lasted for more than one day after emergence. Because the pre-oviposition period corresponds to the migratory period in beet webworm, the results suggest that the first two days of adult life in the beet webworm is the sensitive stage during which presumed migrants can be switched to residents by an appropriate environmental cue. During the sensitive stage or not, starvation did not influence lifetime fecundity, oviposition period, longevity, or egg hatching rate in the starvation-stressed adults. Starvation on the first day also increased tethered-flight performance, and accelerated both flight muscle and ovarian development. The results suggest a pulse of starvation in the sensitive period may inhibit the expected migration by accelerating and compressing the cycle of migratory flight muscle development and degeneration, while accelerating ovarian development, which is normally suppressed until after migration.