Effect of within field topography on emergence of adult sugarbeet root maggot, Tetanops myopaeformis (Roder) (Diptera: Otitidae)

Abstract

The sugarbeet root maggot , Tetanops myopaejormis Roder, is the most important insect pest ofsugarbeet in the Red River Valley of Minnesota and North Dakota. It overwinters as a larva 13 to 22.5 cm deep in the soil. In spring, when soil temperatures increase, the larvae move to within 9 cm of the soil surface, pupate and then emerge as adult flies. Both high and low soil moistures can negatively impact p upal development. Many sugarbeet production areas in the Red River Valley suffer overland flooding during the spring when T. myopaejormis is pupating and standing water within fiel ds is common. Because field topography heavily influences drainage and soil moist ure, it was hy­ pothesized that relative topography within fields can influence the distribution and density ofemerging adult T. myopaejormis. The influence of within field topography on successful pupation of T. myopaejormis was assessed in four commercial fields over two years. Fields were divided into low and high zones, based on the presence of standing water through the period of time when pupation was occurring. A regular grid of emergence traps was used to monitor the adult emergence of T. myopaejormis with additional traps specifically located in standing water zones to sup­ plement the catch data of the grid-placed traps. Resulting trap catches were assessed for spatial autocorrelation using semi-variograms and the geographic information system, ArcView~) was used to construct interpolated surfaces estimating the dis­ tribution and density of emerging adult T. myo­