Mod-04 Lec-19 Biological Control - Microbes: Entomopathogenic Nematodes

Summary

This lecture explores entomopathogenic nematodes (EPNs) as effective biological control agents in integrated pest management. Focusing on the Steinernematidae and Heterorhabditidae families, it explains how EPNs rapidly kill insect hosts by releasing symbiotic bacteria, highlighting their wide host range, durability, and environmental safety. The session covers their mode of action, mass production, and ease of application, while also addressing factors affecting success, such as crop type, pest species, and environmental conditions. The lecture emphasizes that while EPNs are powerful tools, they are most effective as part of a broader IPM strategy rather than a standalone solution.

Takeaways

• 😀 Entomopathogenic nematodes (EPNs) are nematodes that can kill, sterilize, or impede the development of insects by completing at least one life stage inside the host.
• 😀 The main EPN families used in pest management are Steinernematidae and Heterorhabditidae, due to their rapid action and wide host range.
• 😀 EPNs act as carriers of symbiotic bacteria (Xenorhabdus in Steinernema, Photorhabdus in Heterorhabditis) which are responsible for killing the host.
• 😀 The infective juvenile stage of EPNs is free-living, non-feeding, and durable, capable of surviving in soil for months until a suitable host is found.
• 😀 EPNs enter insect hosts through natural openings like the mouth, anus, or spiracles, then release symbiotic bacteria that cause septicemia and death.
• 😀 Once the host is killed, EPNs reproduce inside the insect, and infective juveniles emerge carrying bacteria to infect new hosts, leading to massive multiplication.
• 😀 Advantages of EPNs and microbial biocontrol agents include environmental safety, host specificity, compatibility with chemicals, low cost, mass production, and no reported resistance.
• 😀 Factors affecting biocontrol success include crop tolerance, economic value, crop duration, presence of indigenous or exotic pests, seasonal conditions, and tritrophic interactions.
• 😀 Limitations of biocontrol include the persistence of pest populations above economic thresholds and the need for integrated pest management for overall crop protection.
• 😀 EPNs are a key component of Integrated Pest Management (IPM) rather than a standalone solution due to their species specificity and environmental considerations.

Q & A

What are entomopathogenic nematodes (EPNs) and their role in pest management?

Entomopathogenic nematodes are nematodes that can kill, sterilize, or severely affect the development of insect pests. They complete at least one stage of their life cycle inside the host and are used as biocontrol agents in pest management.

Which families of EPNs are most widely used globally for pest management?

The families Steinernematidae and Heterorhabditidae are most widely exploited globally due to their high host mortality rates, wide host range, and effective symbiotic bacterial associations.

Why are Steinernematidae and Heterorhabditidae preferred over other nematode families?

They cause rapid host mortality within 24–48 hours, have a broad host range of over 200 insect species, are widely distributed, and have a symbiotic association with bacteria that kill the host, making them highly effective biocontrol agents.

How do EPNs kill insect hosts?

Infective juvenile nematodes enter the host through natural openings (mouth, anus, spiracles), release symbiotic bacteria into the hemocoel, which produce toxins leading to septicemia and host death. The nematodes then reproduce inside the host.

What is the infective stage of EPNs and its significance?

The infective stage is the third juvenile stage, which is non-feeding, free-living, durable, and capable of surviving in soil for months. It actively seeks hosts and carries symbiotic bacteria that kill the insect, allowing EPNs to persist in the environment and infect new hosts.

What are the advantages of using EPNs as biocontrol agents?

Advantages include rapid action, wide host range, environmental safety, ease of mass production, long shelf life, easy application, compatibility with chemical insecticides, and no reported resistance development.

What factors affect the success of a biocontrol program using EPNs?

Factors include crop tolerance to insect injury, crop value and duration, presence of indigenous or exotic pests, availability of alternative hosts, seasonal and environmental conditions, presence of hyperparasites, and tritrophic interactions between plant, pest, and natural enemy.

What are the limitations of biocontrol using EPNs?

Limitations include the inability to reduce pest populations completely below economic injury levels, dependence on environmental and biotic factors, and the need for integrated strategies to manage other pests. Biocontrol acts as a component of IPM rather than a complete solution.

How do EPNs contribute to integrated pest management (IPM)?

EPNs provide an environmentally safe, host-specific method to reduce pest populations and can complement chemical or other biological controls. They act as a valuable component within an IPM program rather than being a standalone solution.

What is the role of symbiotic bacteria in EPNs?

Symbiotic bacteria, such as Xenorhabdus in Steinernema and Photorhabdus in Heterorhabditis, are carried by the nematodes and are responsible for producing toxins that kill the insect host. The nematodes serve as carriers and benefit from the nutrients released after host death.

Can EPNs be mass-produced and applied in the field effectively?

Yes, EPNs can be mass-produced using natural hosts or artificial diets. They have a good shelf life, can be applied using conventional sprayers, and remain viable in soil for months, making them effective for field application.

How does the host range of EPNs compare to other microbial biocontrol agents?

EPNs have a very wide host range, affecting more than 200 insect species across 10 orders. This is broader than many other microbial biocontrol agents like fungi, bacteria, or viruses, which often have narrower host specificity.