Rootworm overwintering egg mortality depends not only on soil temperatures, but also on the duration and variability of temperatures. Crop or other vegetation cover and tillage practices will also influence soil temperatures.
Insect Question of the Week
Overwintering Temperatures and Corn Rootworm Egg Hatch?
Eileen Cullen, Extension Entomologist
Sarah Schramm, Associate Research Specialist, Dept. of Entomology
Western and northern corn rootworms overwinter as eggs in the soil. Corey Catt with Nutech/Brownseed mentioned that he has had a couple of questions from clients asking “what temperature will cause corn rootworm eggs to suffer mortal damage in the winter?”. Rootworm overwintering egg mortality depends not only on soil temperatures, but also on the duration and variability of temperatures. Crop or other vegetation cover and tillage practices will also influence soil temperatures.
Woodson and Gustin (1993) determined western corn rootworm eggs need to drop to 23°F or colder to suffer mortality. The longer they are continuously exposed to this constant temperature or cooler, the higher the mortality. This study exposed western corn rootworm eggs to constant low temperatures (32°F, 23°F and 18.5°F) for varying periods of time ranging between 2 and 14 weeks. When eggs were kept at 32°F for 4 weeks, 77% hatched. Egg hatch increased to 83% after 8 weeks at 32°F. At 23°F for 4 weeks, egg hatch was 57%. However, 0% of eggs hatched when held at 23°F for 14 weeks. Finally, eggs kept at 18.5°F for 2 weeks had a 54% hatch rate, but suffered complete mortality (0% hatch) after 8 weeks at 18.5°F.
Chiang’s (1973) review of northern and western corn rootworm egg response to temperature summarized the following. After exposure to 14°F for 1, 2 and 4 weeks; 43% 23% and 0% of eggs hatched, respectively. For western corn rootworms, egg hatch after exposure to 14°F for 1 week was 50%, and no hatching occurred after exposure to 5°F or lower.
In another study (Patel and Apple 1967), northern corn rootworm survival was gradually reduced at 28.4°F as the holding period extended from 2 weeks (90% hatch) to 10 weeks (16% hatch). In the same study, northern corn rootworm eggs suffered complete mortality (0% hatch) at temperatures of 14°F and –9.4°F when exposure reached or exceeded 4 weeks.
Vertically in the soil, corn rootworm eggs are concentrated in the top 6-inches (Patel and Apple 1967; Pruess et al. 1968). Plowing can also disperse the eggs both horizontally and vertically (Chiang 1973).
Soil temperatures vary among tillage systems. Gustin (1981) found moldboard-plowed soils to have lower winter soil temperatures than small-grain stubble plots. Gustin (1981) reported a significant increase in western corn rootworm mortality when eggs were subjected to intermittent temperatures of freezing and thawing. Soils without winter ground cover, for example snow or a crop residue, frequently experience temperature fluctuations of 46 to 50°F (Gustin 1986). In spring, heat accumulation (Degree Days) for rootworm egg hatch may vary for bare soil and soil covered with vegetation. Bare soil needs less time to accumulate Degree Days for egg hatch because it heats up faster (Chiang and Sisson 1968).
Winter temperatures at the rootworm soil depth occur at various intervals and not at constant temperatures. There is a difference between air and soil temperatures, and for the purpose of this discussion we are referring only to soil temperatures. Although winter temperatures cannot be used as a management tool for corn rootworm, the lab studies summarized here provide at least a relative metric to answer the question “how can winter temperatures affect rootworm egg survival?”. Soil temperature and other climate data reports for WI can be accessed at the University of Wisconsin – Extension Automated Weather Observation Network (AWON). This system maintains automated weather stations in WI to provide meteorological data for agriculture and agricultural research: www.soils.wisc.edu/wimnext/awon/awon.html
References Cited
Chiang, H.C. 1973. Bionomics of the northern and western corn rootworms. Annual Review of Entomology 18:47-72.
Chiang H.C. and V. Sisson. 1968. Temperature relationships of the development of corn rootworm eggs. Journal of Economic Entomology 61:1406-1410.
Gustin, R.D. 1981. Soil temperature environment of overwintering western corn rootworm eggs. Environmental Entomology 10: 483-487.
Gustin, R.D. 1986. Effect of intermittent low temperatures on hatch of western corn rootworm eggs (Coleoptera: Chrysomelidae) Journal of the Kansas Entomological Society 59: 569-570.
Patel, K.K. and J.W. Apple. 1967. Ecological Studies on the eggs of the northern corn rootworm. Journal of Economic Entomology 60:496-500.
Pruess, K.P., G.T. Weekman and B.R. Somerhalder. 1968. Western corn rootworm egg distribution and adult emergence under two corn tillage systems. Journal of Economic Entomology 61: 1424-1427.
Woodson W.D. and R.D. Gustin. 1993. Low temperature effects on hatch of western corn rootworm eggs (Coleoptera:Chrysomelidae). Journal of the Kansas Entomological Society 66:104-107.