Question:
The Xenorhabdus symbiont bacterial cells associated with the entomopathogenic nematode Steinernema USA are found in/on the
The Xenorhabdus symbiont bacterial cells associated with the entomopathogenic nematode Steinernema USA are found in/on the
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Remember that Steinernema species carry their symbiotic Xenorhabdus bacteria in a specialized intestinal vesicle (receptacle), whereas Heterorhabditids carry their symbiotic Photorhabdus bacteria throughout the anterior portion of their intestine.
Updated On: Jul 24, 2026
- Oral cavity
- Intestine
- Receptacle
- Cuticle
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The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept:
Entomopathogenic nematodes (EPNs) of the families Steinernematidae and Heterorhabditidae are used as biological control agents against insect pests.
These nematodes have a mutualistic relationship with symbiotic bacteria.
Nematodes in the genus Steinernema associate with bacteria in the genus Xenorhabdus.
The non-feeding third-stage infective juvenile (IJ) carries these bacteria inside its body.
Step 2: Detailed Explanation:
The infective juvenile is the only free-living stage of the nematode that survives in the soil and searches for insect hosts.
Because the IJ has a closed mouth and anus, it cannot feed.
It carries its symbiotic Xenorhabdus bacteria in a specialized, pocket-like structure in the anterior region of its intestine.
This structure is known as the bacterial vesicle or receptacle.
The bacteria remain in this receptacle while the nematode searches for a host.
Once the IJ penetrates a suitable insect host through natural openings (such as the mouth, spiracles, or anus), it enters the hemocoel.
There, the nematode releases the Xenorhabdus bacteria from its receptacle into the insect's hemolymph.
The bacteria multiply rapidly, producing toxins that kill the insect within 24 to 48 hours.
They also produce enzymes that break down the insect's tissues into nutrients that the nematodes feed on as they grow and reproduce.
This specialized receptacle is located in the digestive tract, not in the oral cavity, general intestine, or on the cuticle.
Step 3: Final Answer:
The symbiotic bacteria are carried inside the specialized bacterial receptacle of the infective juvenile.
Thus, the correct choice is (3).
Entomopathogenic nematodes (EPNs) of the families Steinernematidae and Heterorhabditidae are used as biological control agents against insect pests.
These nematodes have a mutualistic relationship with symbiotic bacteria.
Nematodes in the genus Steinernema associate with bacteria in the genus Xenorhabdus.
The non-feeding third-stage infective juvenile (IJ) carries these bacteria inside its body.
Step 2: Detailed Explanation:
The infective juvenile is the only free-living stage of the nematode that survives in the soil and searches for insect hosts.
Because the IJ has a closed mouth and anus, it cannot feed.
It carries its symbiotic Xenorhabdus bacteria in a specialized, pocket-like structure in the anterior region of its intestine.
This structure is known as the bacterial vesicle or receptacle.
The bacteria remain in this receptacle while the nematode searches for a host.
Once the IJ penetrates a suitable insect host through natural openings (such as the mouth, spiracles, or anus), it enters the hemocoel.
There, the nematode releases the Xenorhabdus bacteria from its receptacle into the insect's hemolymph.
The bacteria multiply rapidly, producing toxins that kill the insect within 24 to 48 hours.
They also produce enzymes that break down the insect's tissues into nutrients that the nematodes feed on as they grow and reproduce.
This specialized receptacle is located in the digestive tract, not in the oral cavity, general intestine, or on the cuticle.
Step 3: Final Answer:
The symbiotic bacteria are carried inside the specialized bacterial receptacle of the infective juvenile.
Thus, the correct choice is (3).
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