Question

Which of the following fits the classical definition of an entomopathogenic nematode?
(A) Oscheius
(B) Romanomermis
(C) Heterorhabditis
(D) Deladenus
Choose the correct answer from the options given below:

• A. (A), (C) and (D) only
• B. (B), (C) and (D) only
• C. (C) and (D) only
• D. (A) and (C) only

Hint:

EPNs carry symbiotic bacteria (Xenorhabdus/Photorhabdus) that kill insects within 48 hours.

Answer 1

The Correct Option is D

Classical EPNs:
Heterorhabditis (mutualistic with Photorhabdus bacteria)
Steinernema (not listed)
Oscheius:
Emerging EPN with insecticidal potential
Others:
Romanomermis: Parasitic, not mutualistic
Deladenus: Parasitic to insects but not classical EPN

Answer 2

Applying the classical-EPN criteria to each genus:
A classical entomopathogenic nematode must be an obligate insect killer that carries a mutualistic, insect-pathogenic bacterium released into the host's haemocoel.
Heterorhabditis (C) satisfies both, it is obligately insect-killing and carries symbiotic Photorhabdus bacteria.
Oscheius (A) is increasingly recognised as meeting these same criteria in several species, giving it classical EPN status.
Romanomermis (B) is a mermithid parasite that kills hosts directly without a bacterial partner, and Deladenus (D) is primarily a parasite of wood wasps, not an EPN in the classical sense, both fail the criteria.
Only (A) and (C) satisfy the classical-EPN definition.