MN Fruit & Vegetable IPM News - Vol. 3, No. 2

Although significant infestations of bean leaf beetle (BLB) have not yet been detected in Minnesota snap beans or alfalfa fields, we have been finding beetles on yellow sticky cards (Hastings, MN) the past few weeks, indicating that adults are slowly becoming active. As we continue to monitor fields for infestations one question that arises is whether we can predict the degree to which insects survive winter conditions in Minnesota and how we might use that information to better manage pests during the growing season. For BLB, entomologists at Iowa State University developed a model that, based on average air temperatures during the winter months, can predict what percentage of the population may have been killed during the winter months.

Over a four year period, in Minnesota, we conducted experiments during the winter by placing BLB in cages with leaf litter, and placing the cages in wooded areas along field edges (see image, left). Each month we monitored max./min. temperatures and survival that occurred in each cage, and developed a modified model of BLB winter survival (Carrillo et al. 2005; see table). The model accumulates the number of "cooling” degree days below a base mean daily temperature of 37° F and based on that predicts survival. Even though the winter of 2005-2006 felt much milder than we typically expect in Minnesota, there is still significant mortality to insects. For BLB, however, the mortality has been relatively low, with predicted mortality ranging from 47-49% for southern MN locations. Compared with the winter of 2004-2005 at Lamberton and Rosemount, MN, mortality rates 2005-2006 are quite similar (table). Does this mean infestations of BLB will be similar to the relatively high infestations we observed last year? We can't say for sure due to many other factors that also contribute to insect mortality and movement. However, the model does provide a baseline for future comparisons, and with the opportunity to compare summer infestations with previous winter survival data, this should allow us to make more reliable predictions.

Predicted overwintering mortality of BLB for selected locations in MN
Location (South to North)	% Mortality 2004-2005	% Mortality 2005-2006*
Blue Earth		46.5
Waseca		48.6
Lamberton	47.2	47.3
Rosemount	48.9	47.8
Morris		57.9
Crookston		61.2
*Model used mean daily temperatures for the period September 21, 2005 to May 1, 2006

Source, further reading:

Carrillo, M., R. Koch, E.C. Burkness, K. Bennett, D. Ragsdale & W.D. Hutchison. 2005. Supercooling point of bean leaf beetle (Coleoptera: Chrysomelidae) in Minnesota and a revised predictive model for survival at low temperatures. Environ. Entomol. 34: 1395-1401.

Rice, M.E. 2006. Bean leaf beetles: A historical perspective. ICM Newsletter, ISU. Ames, IA On-line: http://www.ipm.iastate.edu/ipm/icm/2006/5-1/beetle.html

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ACKNOWLEDGEMENTS

Co-Editors: Bill Hutchison (hutch002@umn.edu), Department of Entomology, University of Minnesota, Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Management and Development Division, and Suzanne Wold-Burkness (woldx018@umn.edu), Department of Entomology, University of Minnesota

The Newsletter is published weekly from May through August, cooperatively, by the Minnesota Department of Agriculture (MDA) and the University of Minnesota (U of MN). Reports are posted on the U of MN and MDA web sites on Fridays. If you have suggestions and/or comments, please send your contributions by 4 p.m., Wednesday to Jean Ciborowski, 651-201-6217, jeanne.ciborowski@state.mn.us, MDA, 625 Robert St. North, St. Paul, MN 55155-2538. You can access the Newsletter at the U of MN web site in htm format at: www.vegedge.umn.edu/MNFruit&VegNews/mnindex.htm and at the MDA web site in pdf format at: http://www.mda.state.mn.us/ipm/ipmnews/

Partial funding for this publication is provided through partnership agreements with the Minnesota Fruit and Vegetable Growers Association (MFVGA) and the United States Department of Agriculture – Risk Management Agency (RMA). These institutions are equal opportunity providers.

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Can We Expect High Bean Leaf Beetle Infestations in 2006? Assessing the Results of an Overwintering Mortality Model

Can We Expect High Bean Leaf Beetle Infestations in 2006?
Assessing the Results of an Overwintering Mortality Model