MSU OPM: How to Rear Nematodes for Biocontrol

Summary

This video, produced by Michigan State University's Organic Pest Management Laboratory, outlines the process of rearing entomopathogenic nematodes to control soil insects. It covers the essential steps from assessing nematode populations, infecting hosts (wax worms), and using white traps for nematode extraction, to harvesting and storing the nematodes. The video also explains how farmers can rear their own nematodes as a cost-effective and sustainable alternative to purchasing them. Key considerations such as species selection, infection rates, and application methods are also discussed to ensure successful pest management.

Takeaways

• 😀 Entomopathogenic nematodes are semimicroscopic, unsegmented roundworms that parasitize insects, killing them with the help of a mutualistic bacterium.
• 😀 These nematodes reproduce within the host, completing 1–3 generations before emerging as infective juveniles to find new hosts.
• 😀 They are safe for non-target species, making them an effective biological control for soil-dwelling pests.
• 😀 Farmers may rear their own nematodes to reduce costs, obtain certified organic supplies, or harvest wild nematodes for use.
• 😀 Rearing requires equipment like magnifying lenses, micropipettes, Petri dishes, filter papers, tissue flasks, wax worms, and deionized water, though home alternatives are possible.
• 😀 The rearing process involves four main steps: population density assessment, host infection, white trap extraction, and nematode harvesting and storage.
• 😀 Population density is assessed by sampling a nematode colony, counting them under a microscope, and averaging the counts to determine nematodes per microliter.
• 😀 Hosts (wax worms) are infected at a rate of 20 nematodes per host, with proper labeling, moisture, and storage in dark, warm locations for one week.
• 😀 White trap extraction involves placing infected hosts in a small Petri dish within a larger water-filled dish to collect emerging nematodes over 3–4 weeks.
• 😀 Harvested nematodes are stored in tissue flasks under dark, room-temperature or cooler conditions, with oxygenation recommended for longer storage.
• 😀 Nematodes are applied to soil using sprayers without filters, with site-specific application, avoiding UV exposure, and maintaining soil moisture to ensure survival.
• 😀 Different nematode species have different behaviors and storage capacities; for example, Steinernema species can last 6–12 months, while Heterorhabditis lasts 3–6 months.

Q & A

What are entomopathogenic nematodes and how do they interact with their host?

Entomopathogenic nematodes are semimicroscopic, unsegmented roundworms that parasitize insects. They infect their host as infective juveniles, release mutualistic bacteria that kill the host within 1 to 4 days, and then feed and reproduce inside the host cadaver before emerging to find new hosts.

Why are entomopathogenic nematodes considered effective biological control agents?

They are considered effective because they have negligible effects on non-target species, making them safe and environmentally friendly for controlling insect pests.

What are some reasons a farmer might choose to rear nematodes on-site instead of purchasing them?

Farmers may rear nematodes themselves because purchasing them can be expensive, certified organic supplies are hard to obtain, and there is potential to collect and rear nematodes directly from the wild.

What equipment is required for rearing entomopathogenic nematodes?

The process requires a 10x magnifying microscope or lens, 0–200 µL micropipette, 160 mm and 60 mm Petri dishes, filter papers, 250–500 mL and 1 L tissue flasks, wax worms as hosts, and deionized water. Alternative household equipment can also be used.

What are the four major steps in the nematode rearing process?

The steps are: 1) assessing population density, 2) infecting hosts with nematodes, 3) extracting nematodes using the white trap method, and 4) storing the harvested nematodes for future use or reinfection.

How is population density of nematodes determined?

Population density is assessed by taking a sample of the nematode solution with a micropipette, placing it on a gridded Petri dish with deionized water, counting the number of moving nematodes under a microscope, repeating three times, and averaging the counts per microliter.

Why are wax worms used as hosts for nematodes?

Wax worms are locally available, reliable, and easy to handle, making them suitable for laboratory infection of nematodes.

What is a white trap and why is it used?

A white trap involves placing a small Petri dish with infected hosts inside a larger dish filled with water. Nematodes emerge from the host cadavers into the water, allowing easy collection for storage and reuse.

How should nematodes be stored after harvesting?

Nematodes should be stored in tissue flasks in a dark, room-temperature location for 3 weeks to 2 months. Cooler storage with aeration using an air pump and an AirStone is recommended for longer-term storage, with Steinernema species lasting 6–12 months and Heterorhabditis species 3–6 months.

What are the best practices for applying nematodes in the field?

Nematodes should be applied directly to the soil using sprayers with filters removed, preferably in the early morning or evening to avoid UV light. Soil should be kept moist, and applications should consider site-specific conditions, as nematodes disperse only about 90 cm within 30 days.

How does the biology of different nematode species affect their use?

Different species have different foraging strategies: Steinernema carpocapsae is an ambush predator near the soil surface, Heterorhabditis bacteriophora is a forager, and Rhabditis species fall in between. Matching nematode species to target pest ecology is crucial for effective pest management.

What factors can affect the survival and effectiveness of nematodes in soil?

Nematodes are sensitive to UV light, extreme temperatures (below 68°F or above 86°F), and require adequate soil moisture for survival. Soil pH has minimal effect on their effectiveness.