Effect of Straw Mulch on Populations of Microtheca ochroloma (Coleoptera: Chrysomelidae) and Ground Predators in Turnip Brassica rapa in Florida

Microtheca ochroloma Stål (Coleoptera: Chrysomelidae), the yellow-margined leaf beetle, is a serious pest of crucifer crops in the southeastern USA. The objective of this study was to investigate the effect of straw mulch on the abundance of M. ochroloma and ground predators in turnips in Florida, and subsequent influence on crop damage and yield. Eight plots (5 m long × 9 m wide) were established, and each plot consisted of 5 beds with 10 turnip plants each (50 turnips per plot). An 8–10-cm layer of straw mulch was applied by hand 2 d after planting to half of the plots in a complete randomized block design. The abundance of M. ochroloma and other insect herbivores were recorded twice weekly from Mar 13 to Apr 24, 2009. In addition, 3 pitfall traps per plot were used for sampling predatory arthropods during each sampling period. Higher numbers of M. ochroloma were found in plots with mulch compared to plots with no mulch, whereas greater numbers of ground predators were obtained in the no mulch treatment. The most abundant predators found in pitfall traps were ants, earwigs, and spiders, while lower numbers of predatory beetles were recorded. At the end of the experiment, greater leaf biomass (dry weight) was obtained from turnip plants grown in plots with straw mulch, but those plants suffered greater herbivory since the leaf area removed was greater in that treatment. Mean weight of tubers did not vary significantly between treatments. In conclusion, the use of straw mulch as a pest management option for M. ochroloma in crucifer crops on organic farms is not recommended.