UPSC Prelims 2024 Q18: Parasitoid Organisms — Explained
Consider the following:
1. Carabid beetles
2. Centipedes
3. Flies
4. Termites
5. Wasps
Parasitoid species are found in how many of the above kind of organisms?
- Only two
- Only three
- Only four
- All five
Answer: (b) Only three
Statement-wise explanation
- 1: correct — Most ground beetles (family Carabidae) are predators, but a few are parasitoids. Three of the 76 carabid tribes (Brachinini, Peleciini and Lebiini) have larvae that live as ectoparasitoids on beetle pupae and kill them. Bombardier beetles of the genus Brachinus develop on the pupae of water beetles and Amara ground beetles. Lebia grandis does the same to Colorado potato beetle pupae.
- 2: incorrect — Centipedes (class Chilopoda) are not insects. They are predatory arthropods that kill prey with venom delivered through modified front legs called forcipules. No centipede species grows inside or on a single host and kills it, so the group has no parasitoids.
- 3: correct — Flies (order Diptera) hold roughly 15% of all known parasitoid species, second only to Hymenoptera. Tachinid flies, the best-known group, lay eggs on or in caterpillars and other insects. Their larvae eat the host from inside and kill it.
- 4: incorrect — Termites are social insects that eat plant matter such as wood, leaf litter and humus, often with the help of gut microbes or cultivated fungus. They are hosts that parasitoids attack, not parasitoids themselves. No termite species lives off and kills an individual host.
- 5: correct — Wasps (order Hymenoptera) are the classic parasitoids. About 80% of all parasitoid species belong to this order, in families such as Ichneumonidae, Braconidae, Chalcididae and Trichogrammatidae. India's biological-control programmes mass-rear Trichogramma egg parasitoids against crop borers.
How to eliminate
Two items can be settled from basic knowledge. Parasitoid wasps (for example, Trichogramma in biocontrol) and parasitoid flies (tachinids) appear in standard textbooks, so flies and wasps are both in. That rules out 'only two' unless you wrongly drop one of them. Termites are plant-feeding social insects, and centipedes are venomous free-living predators that are not insects at all. Excluding both rules out 'all five' and leaves the carabid beetle as the deciding item. Here you need one fact: a few carabid genera, Lebia and Brachinus (bombardier beetles), have larvae that are ectoparasitoids of other beetles' pupae. Remember it as: parasitoids occur among wasps (about 80% of species), flies (about 15%) and a handful of beetles, including some carabids.
Know more
Parasitoid vs parasite vs predator
A parasitoid spends its larval stage feeding on or inside a single host and finally kills it. The adult usually lives freely and feeds on nectar or honeydew. A true parasite (a tick, a tapeworm) normally keeps its host alive. A predator (a ladybird, a centipede) kills and eats many prey animals during its life.
| Feature | Parasite | Parasitoid | Predator |
|---|---|---|---|
| Hosts/prey per individual | One or a few | One (larval stage) | Many |
| Kills the host? | Usually not | Yes | Yes, immediately |
| Example | Louse, tapeworm | Trichogramma wasp, tachinid fly | Ladybird beetle, centipede |
Where parasitoids occur
Parasitoidism is found in seven holometabolous insect orders:
| Order | Share / examples |
|---|---|
| Hymenoptera (wasps) | About 80%: ichneumonids, braconids, chalcids, Trichogramma |
| Diptera (flies) | About 15%: Tachinidae, some Sarcophagidae and Bombyliidae |
| Coleoptera (beetles) | A few: Lebia, Brachinus (Carabidae), Rhipiphoridae |
| Others | Strepsiptera, a few Lepidoptera, Neuroptera, Trichoptera |
Endoparasitoids develop inside the host and ectoparasitoids feed from outside it. Idiobionts stop the host's development at once, while koinobionts let it keep growing.
Why it matters: biological control
Parasitoids are a core part of Integrated Pest Management (IPM) in India. State biocontrol laboratories and the Central Integrated Pest Management Centres rear and release Trichogramma (egg parasitoids of sugarcane, rice and cotton borers) and other parasitoids. They also protect them in the field by cutting back broad-spectrum pesticides. Biocontrol reduces pesticide residues and the build-up of pest resistance.
NCERT Concepts to Revise
- Biopest control: Parasitoid wasps and flies are the main living agents used in biopest control, which explains why UPSC tests this group of organisms.
- Integrated pest management: IPM is the framework in which parasitoids are mass-reared and released against crop pests in India.