Long-term Flow Patterns of the Twelve-spotted Ladybeetlein an Agricultural Landscape

Marchbanks, S.A., M. Colunga-Garcia, and S.H. Gage.

Presented at the All Scientist Meeting (2002-10-04 )

The life system of the twelve-spotted ladybeetle (Coleomegilla maculata) involves the presence of aggregation sites in or adjacent to wooded areas during the winter, and feeding and reproduction sites in the early spring or summer, with temporal patterns of movement and dispersion among the different habitats.  Tree-related habitats can be a potential aggregation site if it has a southern exposure, is located near agricultural fields, and is not subject to human disturbance.  Hedgerows and woodlots harbor the major aggregates if neighboring fields during the previous season were corn or alfalfa.  Fewer numbers are expected if neighboring fields were soybeans.  C.maculata use aphids as a main source of food, but it can also feed on eggs and larvae of several coleopterans and lepidopterans, and on pollen from several sources.  Winter wheat and alfalfa are habitats available early in the growing season, while corn is available for the beetles later on. Since 1989, trap catches of C.maculata have been collected weekly from yellow sticky-traps, and recorded in a database.  There are seven agricultural treatments at the KBS LTER site, in which four are annual corn-soybean-wheat rotations managed with a range of chemical-input intensities.  The maps in the graph below were created using ArcView® GIS, and illustrate the differences in average trap capture of the insect over a spatial and temporal dimension.  The treatment maps that correspond to each year show the possible correlation between high insect counts and certain agricultural treatments.  Corn appears to be the crop that is most closely associated with high average trap captures in plots with CT, NT, LCI, and ZCI treatments.  When corn/soybean or soybean/wheat rotations are present in certain years, plots with poplars and alfalfa treatments tend to have high concentrations of C. maculata.

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