Two flea beetles, Aphthona lacertosa Rosenhauer and A. nigriscutis Fourdas, are biological control agents introduced to control leafy spurge, Euphorbia esula L., in North America. Understanding phenological patterns, in particular predicting peak abundance, provides researchers and land managers information on when to collect agents for redistribution. To develop this model, three steps were required: 1) determine lower developmental threshold for each species, 2) estimate peak emergence in the field for each species using accumulated degree-days (ADD), and 3) develop statewide maps that spatially represents predicted occurrence of peak abundance. Lower developmental thresholds (LDT) were determined through controlled growth chamber experiments where field collected soil cores containing diapausing beetle larvae were held at 15,18, 21, 24, and 27º C. Average days to adult emergence were determined for each temperature and applied to a linear regression model to predict the lower developmental threshold. The LDT for Aphthona lacertosa and A. nigriscutis are 8.3 and 10.1º C, respectively. Twenty-six field sites were sampled for adult flea beetle abundance weekly during June and July in 2000, 2001 and 2002. A non-linear stochastic model was used to describe proportional seasonal abundance as a function of ADD (based on previously determined LDT). Peak adult abundance for Aphthona lacertosa and A. nigriscutis occurred at 512 ADD and 610 ADD, respectively. Using thirty-year adjusted normal temperature data from 172 weather stations in Minnesota, a contour map of estimated peak emergence dates was developed to alert resource managers when to collect and redistribute insects in their area.
Species 1: Coleoptera Chrysomelidae Aphthona lacertosa
Species 2: Coleoptera Chrysomelidae Aphthona nigriscutis
Species 3: Euphorbiales Euphorbiaceae Euphorbia esula (Leafy spurge)
Keywords: GIS, developmental rates
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