Advances on managing spotted wing drosophila with entomopathogenic nematodes
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EmailBiological control agents, mainly entomopathogenic nematodes, are a great alternative to chemical insecticides for managing spotted wing drosophila.
Until 2010, Michigan’s blueberry integrated pest management (IPM) program was a sustainable system that targeted the main blueberry pest complex: cranberry fruitworm, cherry fruitworm, blueberry maggot and Japanese beetle. After the arrival of spotted wing drosophila (SWD), insecticide applications increased to more than 10 per season, and pest management expenses went from $75 per acre to $456 per acre in 2014. In response, the Michigan State University Extension blueberry IPM program started on-farm trials to assess the performance of entomopathogenic nematodes (EPNs) and soil dwellers.
Objectives
- To incorporate EPNs and soil dwellers into current IPM programs for controlling SWD.
- To reduce insecticide applications and associated expenses by at least 50%.
- To reduce fruit losses and help small blueberry farms and industry to produce sustainably and cost effectively.
Biological control for SWD management
Biological control agents are a great alternative to chemical insecticides, but the economic threshold for pest damage in blueberries is zero. This becomes a limiting factor to using biological control agents alone. However, incorporating biological control agents under a systems approach could increase pest mortality and help reduce the negative risks of relying on chemical control alone. This results in prohibitive costs for the environment and increased farmers, workers and consumers exposure, and development of pest resistance.
Selecting biological control agents
Selecting the EPN Steinernema feltiae was based on efficacy results obtained from preliminary laboratory tests. Among three commercial EPN species evaluated (S. feltiae, S. carpocapsae and Heterorhabditis bacteriophora), S. feltiae caused the highest mortality of SWD larvae and pupae (78% and 65%, respectively). We included in one treatment the soil dweller Dalotia coriaria (previously known as Atheta coriaria) and Stratiolaelaps scimitus (previously known as Hypoaspis miles) to evaluate their effectiveness alone or in combination with ENPs (Photo 1). These biological control agents can also prey on thrips and other Diptera, allowing introductions prior to the arrival of SWD.
Farms selected in 2023-2024
We selected two types of farms. One was a commercial farm under conventional management and the other was a farm under 100% organic management with zero pesticide applications.
Conventional farm, variety keepsake
Treatments were as follows:
- Standard chemical control, one application Lannate + 4 applications Mustang Maxx
- Steinernema feltiae
- Steinernema feltiae + soil dwellers (Dalotia coriaria and Stratiolaelaps scimitus)
- Soil dwellers (Dalotia coriaria and Stratiolaelaps scimitus)
Organic pesticide-free farm, variety Jersey
Treatments were as follows:
- Control: untreated
- Steinernema feltiae
- Steinernema feltiae + soil dwellers (Dalotia coriaria and Stratiolaelaps scimitus)
Biological control agent rates were as follows:
- Steinernema feltiae: 500 million to 1 billion two to three times per season
- Dalotia coriaria (Atheta- System): 0.1 to 0.05 per square feet once per season
- Stratiolaelaps scimitus (Hypoaspis-System): 5 to 10 per square feet once per season.
The arrival and population dynamics of adult SWD were monitored weekly using traps baited with a Pherocon SWD lure (Trécé).
We evaluated fruit infestation per treatment at the first harvest: For this purpose, we collected six 1-pound fruit samples at random from each treatment. We submerged individual samples in a saline solution for 30 minutes. We collected all larvae plus eggs exiting the slightly crushed fruit by sieving the water using a coffee filter and counted.
Results
Applying EPNs (Steinernema feltiae) alone or in combination with the soil dwellers (Dalotia coriaria plus Stratiolaelaps scimitus) effectively reduced SWD adult population and fruit larval infestations at all treatments plots.
At the organic farm, applying ENPs reduced the SWD adult populations by about 60% in comparison with the untreated control. On the other hand, at the conventional chemically treated farm, the reduction was 41.5%. Regarding larval infestations at harvest, the reduction at the organic farm was between 30-50% in comparison with the untreated control. Likewise, at the conventional farm, the reduction was between 50-80% in comparison with the chemically treated control.
All biological control agents used are native species and could have the potential to overwinter and continue reproducing in successive seasons. The systems approach reduced insecticide applications by at least 50% while improving control, and could therefore be an economically viable and sustainable alternative for Michigan’s blueberry growers.
Downloadable poster
Growers can download the following poster that describes these trials, which was presented at the 2024 Great Lakes EXPO in Grand Rapids, Michigan, on Dec. 10-12, 2024.
