Wireworms are immature stages of click beetles (Coleoptera: Elateridae) and are considered a serious threat to sweet potato production in the southern United States. The major wireworm species collected in North Florida sweet potato fields in 2017 and 2018 were Conoderus scissus, C. rudis, C. amplicollis, and C. falli. These species vary in their behavior and biology. During a 2-yr study period, we conducted two insecticide field trials using eleven insecticides belonging to organophosphates, neonicotinoids, pyrethroids, and botanical classes, and three field trials using entomopathogenic nematode (EPN) species to control wireworms. In 2017, all insecticide treatments significantly reduced new feeding holes and total holes (old + new + other) as compared to the untreated control. In 2018, the result was similar with a few variations. In both years, all insecticides showed a percentage reduction in wireworm damage holes (2017: 34.88–96.19%; 2018: 12.38–97.02%) with the highest by Regent. In the EPN field study, one application of EPN near planting significantly reduced soil insects. In a laboratory study conducted at the Tropical Research and Education Center, UF-IFAS, chlorpyrifos caused higher percentage mortality of C. rudis (55.5%) than C. scissus (22.2%). At the present experiment rates, none of the insecticides caused the mortality of C. amplicollis. Heterorhabditids strain ‘FL-2122’ was more susceptible to chlorpyrifos than other strains of EPN.
SummaryNematode parasitism is a yield limiting factor in many cropping systems, including potato production, which can translate into substantial economic losses. These impacted financial returns are simply calculated by subtracting the cost of production from total revenue (yield times the price per yield of potatoes). The production costs can include, but are not limited to, chemical and biological control agents. To assess economic returns associated with different nematode management strategies, we evaluated complete cost estimations for a representative commercial potato farm in central Michigan, USA. Economic returns were calculated using stochastic parameters for two biological control agents (MeloCon and Majestene), six chemical controls (Mocap, Movento, Nimitz, Velum and Vydate), and two soil amendments (poultry and dairy manure). Evaluated costs included stochastic estimations for price per unit weight of potatoes, fuel, labour and production land rent. Yield data from three field trials were used to create empirical distributions. Using yield data and stochastic cost estimations, we generated 500 simulations of net returns per treatment. The top three average returns were obtained from the use of Mocap, Nimitz and poultry manure. Velum, Movento, dairy manure and Vydate also gave returns significantly higher than no treatment at all; however, the biological nematicide, Majestene, showed negative returns. This simple financial model is a crucial layer of analysis on the performance of nematicides that can be adapted to advise growers through Agricultural Extension activities and needs to include the evaluation of biological control agents.
Endospore-forming bacterium in the genus Pasteuria spp. infect multiple agriculturally significant plant parasitic nematodes and has potential as a potent biological control. Success as a biological control requires not only spore attachment to the cuticle, but sporulation and reproduction within the nematode host. Tracking and identifying Pasteuria spp. development is then critical to demonstrating efficacy as a biocontrol. Microscopic observations suggest Pasteuria spp. follows the model bacterium, Bacillus subtilis, sporulation. Here, we identified B. subtilis homologs of sporulation regulators in Pasteuria spp. and characterized the temporal expression of these genes throughout the bacterium's ∼ 30-d lifecycle in Meloidogyne arenaria as a means of tracking sporulation development. Detectable levels of transcripts of Spo0F were present as early as 5 d after the nematodes were exposes to Pasteuria spp. and were relatively constant throughout the 30-d lifecycle. Transcripts to Sigma-F were significantly higher in the middle of the lifecycle, while the transcripts of Sigma-G were detectable between 15 and 25 d, nearing the end of the lifecycle. These three markers can be used to track the process of sporulation in the nematode and augment microscopic observations. Tracking sporulation of Pasteuria spp. is important to fully realize its potential as a biological control method as it can more readily identify successful parasitism, define host ranges, and inform in vitro growth progress.
Includes: Introduction - Distribution - Description - Life Cycle and Biology - Hosts - Economic Importance - Management - Selected References Also available in the Featured Creatures collection at: http://entnemdept.ufl.edu/creatures/NEMATODE/Pasteuria_penetrans.html
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