Egg hatch and survival and development of beet webworm (Lepidoptera: Crambidae) larvae at different combinations of temperature and relative humidity

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

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2016
Publication Date: 8/1/2016
Citation: Tang, J., Cheng, Y., Sappington, T.W., Jiang, X., Zhang, L., Luo, L. 2016. Egg hatch and survival and development of beet webworm (Lepidoptera: Crambidae) larvae at different combinations of temperature and relative humidity. Journal of Economic Entomology. 109(4):1603-1611. doi:10.1093/jee/tow106.

Interpretive Summary: The beet webworm is an agricultural pest of several crops, including corn, in Asia and North America. It overwinters as a full grown caterpillar 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, so when factors such as temperature and relative humidity affect reproductive traits like egg hatch and larval survival it also can indirectly, but strongly, affect migratory decisions and timing, as well as population dynamics in the area invaded by migrants. In this study, eggs and larvae were held at different combinations of temperature and relative humidity in the laboratory to determine the effects on immature survival and development rates. The optimal temperature was determined to be 22oC, which explains a number of field observations including why outbreaks of beet webworm only occur in areas with a prevailing mean temperature around 22oC. Furthermore, relative humidity in the range of 60-80% was optimal, explaining observations of host plant preference by egg-laying females and positioning of eggs on the plants, which take advantage of the most favorable microclimates for offspring survival and development. This information will be used by university and government scientists in the U.S., China, and throughout the world to better understand the mechanisms promoting population outbreaks by migratory insect pests, and thus lead to better methods for their prediction and management.

Technical Abstract: To understand the role that temperature and humidity play in the population dynamics of the beet webworm, Loxostege sticticalis L. (Lepidoptera: Crambidae), egg hatchability, survival of 1st - 5th instars, survival of the complete larval stage, survival curves, and larval development rates were investigated at combinations of 4 temperatures (18, 22, 26 and 30') and 5 relative humidities (RH) (20%, 40%, 60%, and 100%). We found that greatest egg hatchability, survival rates of the 1st and 2nd instars, and survival rate of the complete larval stage occurred at 22' and 60 - 80% RH; the lowest values for these parameters were observed at 30' and 20% RH. Survival of 1st instars was significantly affected by the interaction of temperature and relative humidity. However, survival of 3rd and 4th instars was affected by neither temperature nor relative humidity, and that of 5th instars was significantly affected only by relative humidity level. The survival curve for larvae fitted by the Weibull distribution was type III. Duration of larval stage decreased as temperature increased, but was not affected by relative humidity. We therefore conclude that eggs and early instars are the most critical stages for survival to the pupal stage, and 22' and 60-80% RH are the optimum conditions for their survival and development. These findings confirm that temperature and relative humidity are the critical environmental factors affecting the population growth of L. sticticalis, with temperature being more important.