Biological control and protozoa — members of which protozoan group are investigated as biological control agents against insect pests?

Introduction:
Some protozoan groups include obligate intracellular parasites of insects. These organisms can reduce pest populations and are studied as biological control agents.

Given Data / Assumptions:

• Target is “biological control of insects.”
• We compare several protozoan phyla.

Concept / Approach:
Microsporidia (historically placed among protozoa; now often considered fungi-related) are well-known insect pathogens used or explored in biocontrol programs (e.g., Nosema spp.). Apicomplexans infect many vertebrates and invertebrates, but microsporidia have the strongest record for insect biocontrol.

Step-by-Step Solution:

Verification / Alternative check:
Entomological literature cites Nosema locustae for orthopteran control; multiple Nosema species infect lepidopterans and dipterans.

Why Other Options Are Wrong:

• Sarcomastigophora: few cases as formal biocontrols.
• Apicomplexa: less established for deliberate control.
• All of these: overbroad given practical usage.

Common Pitfalls:
Assuming any parasite of insects is automatically a biocontrol agent; practical deployment history matters.

Final Answer:
Microspora (microsporidia)