Parasitoids

Parasitoids

A parasitoid is an organism that, during its immature stages, lives in or on a host, ultimately causing the host’s death. Parasitoids share characteristics of both parasites and predators—like parasites, they depend on a host for part of their life cycle, but like predators, they eventually kill the host.

Basic Characteristics of a Parasitoid

1. Host Dependency – Parasitoids require a host for development but not for reproduction.
2. Lethal Effect – Unlike true parasites, parasitoids kill their host before completing their life cycle.
3. Specialized Relationship – Most parasitoids exhibit high host specificity, often attacking only one or a few species.
4. Larval Stage Parasitism – The immature stages (larvae) feed on the host, while adults are free-living.
5. Delayed Lethality – The host remains alive during most of the parasitoid's development but is eventually consumed or killed.
6. Parthenogenesis – Some parasitoids reproduce without fertilization (as seen in certain wasp species).

 

Parasitoids in Different Insect Orders

1. Order Hymenoptera (Wasps, Bees, Ants)

• The most diverse and dominant group of parasitoids.
• Includes Braconidae, Ichneumonidae, and Chalcididae families.
• Many species lay eggs inside or on insect hosts.
• Example: Cotesia glomerata (a braconid wasp) parasitizes caterpillars.

2. Order Diptera (Flies)

• Parasitoid flies mainly belong to the Tachinidae family.
• Often use injecting eggs or larvae into host bodies.
• Commonly parasitize caterpillars, beetles, and other insects.
• Example: Tachina fera, a tachinid fly that parasitizes moth larvae.

3. Order Lepidoptera (Butterflies and Moths)

• Some moth larvae exhibit parasitoid-like behavior by feeding on living hosts.
• Few known cases exist compared to other insect orders.
• Example: Epipyropidae (a moth family) parasitizes cicadas.

4. Order Coleoptera (Beetles)

• Few beetles exhibit parasitoidism, mainly in the Ripiphoridae and Rhipiceridae families.
• Larvae are typically endoparasitic on other insects.
• Example: Ripiphorus beetles parasitize wasps.

5. Order Strepsiptera (Twisted-Wing Parasites)

• Obligate endoparasites of bees, wasps, and other insects.
• Males emerge as free-living winged adults, while females remain embedded in the host.
• Example: Xenos vesparum, a parasitoid of paper wasps.

Significance of Parasitoids

1. Biological Control Agents

• Used in agriculture and forestry to control pest populations.
• Example: Trichogramma wasps control crop-damaging caterpillars.

2. Ecological Balance

• Regulate insect populations in natural ecosystems.
• Prevent outbreaks of herbivorous pests.

3. Evolutionary Importance

• Co-evolution between parasitoids and hosts drives adaptations like immune defenses in hosts and counter-strategies in parasitoids.

4. Research and Medicine

• Studied for understanding host-parasite interactions.
• Potential use in biotechnology and pest management.