SEASONAL FLUCTUATIONS IN THE BENEFICIAL ARTHROPOD COMPLEX ASSOCIATED WITH CONVENTIONAL TILLED AND ZONE TILLED SUGAR BEETS

Johan Pretorius, Jeff Bradshaw, Gary Hein
2013 American Society of Sugarbeet Technologist   unpublished
The species composition and relative abundance of the natural enemy complex encountered in conventional tilled and reduced tilled sugar beets have not been investigated to any great extent for the sugar beet production regions of western Nebraska. Variations in the abundance and species composition of these beneficial organisms throughout the season, both within a particular tillage system and between different tillage practices, could potentially lead to differences in the degree of ecosystem
more » ... ervices rendered. This ongoing study aims at determining the beneficial arthropod complex and their relative abundance over the growing season in conventional tilled and zone tiled sugar beets in western Nebraska. It also aims at measuring the degree of ecosystem services rendered by arthropods in these two tillage regimes, as it relates to weed seed-removal and prey-removal. Methodology: Pitfall traps were used to monitor the activity-density of soil-dwelling predatory arthropods in conventional till and zone till sugar beets, starting in 2012. Each cultivation type was replicated five times, with six pitfall traps installed per plot. The traps were activated for a total of six times during the season and left open for five consecutive days. To determine the rate of weed seed-removal, four weed species were selected, namely two grasses (Yellow foxtail and Barnyardgrass) and two broad-leaf weeds (Common lambsquarters and Kochia). Seeds of these weed species were attached to petri-dishes by means of double-sided tape and placed into vertebrate exclosure cages in the field. Four petri dishes were included in each cage, each petri dish containing the seeds of a single weed species. Three cages were placed in each plot along with a control cage. The seeds were left in the field for ten consecutive days. Concomitant to the weed seed-removal study, a prey-removal study using waxworms (Galleria mellonella) as surrogate prey was also carried out. Larvae were pinned to a clay base and three larvae were placed in each exclusion cage. Two sampling periods were selected, namely a day sampling period Results from the pitfall trapping showed that ground beetles (Coleoptera: Carabidae) were the most abundant beneficial taxa collected throughout the season in both tillage types (n = 2,043 individuals in the conventional tilled sugar beets and n = 1,674 individuals in the zone tilled sugar beets). Other abundant beneficial taxa included centipedes (Class: Chilopoda), staphylinid beetles (Coleoptera: Staphylinidae), and spiders (Order: Araneae). Overall, ground beetles did not show a preference for any particular tillage practice (F=0.63, P=0.45) which could be a function of their higher mobility, permitting free movement between plots subjected to different cultivation regimes. However, their abundance changed significantly throughout the season (F=72.59, P<.0001), rising steadily into mid-August and then dropping abruptly towards the last sampling date in September. Ground beetle species diversity was highest at the beginning of the season in both tillage practices with a total of n = 20 observed species in the conventional tilled plots, and n = 23 species in the zone tilled plots on the second sampling date (08 June). Species composition differed most between
doi:10.5274/assbt.2013.49 fatcat:2c4zjdh3j5cmhp3ibxwm4bvtte