|CHENG, YUNXIA - Chinese Academy Of Agricultural Sciences|
|WANG, KAI - Chinese Academy Of Agricultural Sciences|
|LUO, LIZHI - Chinese Academy Of Agricultural Sciences|
|JIANG, XINGFU - Chinese Academy Of Agricultural Sciences|
Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2015
Publication Date: 10/28/2015
Citation: Cheng, Y., Wang, K., Sappington, T.W., Luo, L., Jiang, X. 2015. Response of reproductive traits and longevity of beet webworm to temperature, and implications for migration. Journal of Insect Science. 15:154 doi:10.1093/jisesa/iev135.
Interpretive Summary: The rice leaf roller is a serious pest of rice in Asia, East Africa, and Australia. It is a long-distance migratory species, and outbreaks may occur in areas that receive a large influx of immigrants. For migratory insect species there is a presumed trade-off in energy reserves, in that energy used for long-distance flight is not available for egg production. To manage this trade-off so that egg production is not harmed too severely, many insects delay reproductive development until after migration has occurred, a combination of characteristics called the "oogenesis flight syndrome". However, in some species, this trade-off may be overestimated, because factors like flight behavior and environmental conditions may reduce its effects. In this study, we used flight mills to examine the reproductive consequences induced by different flight scenarios. We found that the influences of flight on reproduction are not absolutely positive or negative, but instead depend on the age at which the moth begins flight, flight duration, and how many consecutive nights they are flown. The results also show that flight synchronizes egg-laying in groups of females that migrate, which may promote high-density larval outbreaks. Other crop pests, including some in North America probably use the same strategy. This information will be used by university and government scientists in the U.S., China, and throughout the world to better understand the mechanisms controlling explosive growth of outbreak insect populations, and thus lead to better methods for their prediction and management.
Technical Abstract: Beet webworm, Loxostege sticticalis (Linnaeus) (Lepidoptera: Pyralidae), is a facultative long-distance migratory insect pest of crops in many regions between latitudes 36-55°N. Reproductive performance of L. sticticalis is very sensitive to thermal conditions, such that outbreaks of larvae are closely related to temperatures encountered by the immigrant adult. But mechanisms linking population outbreaks and migration are not well understood. We investigated the effect of exposing adults to constant temperatures from 14 to 34' on mating, oviposition and longevity. Our results showed that both mating percentage and frequency were highest at 22-26' and decreased at temperatures outside this optimal range. Time of night when mating began was delayed at higher temperatures, while mating duration progressively decreased with increasing temperature. Both preoviposition period (POP) and oviposition period decreased linearly with increasing temperature. Peak daily and lifetime fecundity were highest at 22-26' and declined at temperatures outside this range, suggesting that 22-26' is the optimal thermal range for oviposition. Adult longevity was negatively correlated with temperature. Males lived longer than females at lower temperatures, but females lived longer than males in the 30 to 34' treatments. Together, our findings suggest that reproduction occurs when the prevailing temperature is around 22-26', and that migratory flight is favored outside this range via increases in POP and proportion of virgins. We predict that larval damage or outbreaks of L. sticticalis will occur only in areas where the prevailing temperature is around 22-26', which provides a key basis for the prediction of population outbreaks in areas of immigration.