Parasitoids are a specific type of organism that exhibits a unique and fascinating ecological strategy. In an agroecosystem pest management and defense against natural enemies, and host plant resistance is crucial. Arthropods that are predatory and parasitic kill herbivores to live on plants without causing them significant harm. Recent studies show that some plants that are harmed by herbivores produce chemical signals that notify the herbivores’ natural foes of the issue.
It is improbable that plants harmed by herbivores will begin producing compounds just to entice parasitoids and predators. The signalling function most likely developed later from plant responses that produce herbivore-deterrent poisons, antibiotics, and deterrents against infections.
The theory that plants actively recruit these natural enemies from herbivores depends on the effective utilization of the chemical signals provided by the plants by predators and parasitoids. Amazing plant adaptations that favour the presence of parasitoids and predators can be seen. The finest instances must be the distinctive structures plants like acacias and cecropias have developed that result in mutualistic collaborations with ants.
In these encounters, the plants offer the ants nutritious food bodies and extrafloral nectaries, as well as shelter in hollow stems and thorns. The main benefit that the ants appear to provide to the plants in exchange is a defence against herbivores. The variation in the number of insect pests affecting host plants affects the parasitoids’ population density. An important class of natural enemies of aphids in the field is parasitoids.
What are Parasitoids:
Small insects called parasitoids to grow inside or adhere to the outside of other insects during their immature stages, known as hosts. The host that parasitoids feed on is finally destroyed, as opposed to other parasites like fleas and ticks, which often prey on hosts without killing them.
Types of Parasitoids:
Primary parasitoids
species that develop on hosts that are not parasitized.
Secondary Parasitoids:
A parasite that grows inside another parasite. There could be different stages of hyperparasitism.
Endoparasitoids:
Endoparasitoids are parasitoids that grow and feed inside their host after hatching from eggs or larvae placed there by an adult female.
Ectoparasitoids:
Parasitoids are parasites that attach to the outside of their hosts and eat through their skin to extract bodily fluids. The majority of parasitoids are either wasps and bees (Hymenoptera) or flies (Diptera), although a few species of beetles, twisted-wing insects, moths and other insects have been classified as parasitoids. Many parasitoids are so minute that gardeners might easily miss them, while some are around the same size as their hosts. At the end of a phrase, parasitoid wasps are frequently just as the time.
Multiple Parasitism:
occurrence of many parasitoid species on or inside of a single host. In many instances, only one person survives while others pass away. Occasionally, multiple species of Trichoghramma (parasites of Lepidoptera eggs) can develop to maturity in the egg.
Super Parasitism:
In this situation, a host may become home to several members of a parasitoid species. A dominant individual may survive when superparasitism with solitary endoparasites occurs due to mutual destruction of the physiological suppression of larvae or surplus eggs. But occasionally, the host passes away before the extra is used, and everyone dies.
Adelpho Parasitism:
A parasitoid species that is also a parasite of itself is known as auto parasitism. For instance, in the Coccophagus scutellaris (Dalman), the male must serve as the female’s parasite.
Klepto Parasitism:
In this instance, a parasitoid attack hosts more frequently if they have already been parasitized by another species. It is not a hyperparasitoid, the kleptoparasitic. For better chances of reproduction, a kleptoparasitic relies on another parasite. It can take advantage of these openings, which entails finding the host utilizing oviposition holes or search trails left behind by other parasitoid species.
Heteromes: Each of the male and female parasitoids’ hosts is different.
Polyembryony: Each host receives a single egg from the adult, which later divides into many cells that all develop separately. A parasitized egg develops into many embryos. Encyrtidae and Braconidae are both susceptible to it. Per parasitized egg, the parasitic nematode Ageniaspis citricola of the citrus miner, Phyllocnistis citrella, produces 2–10 individuals. Eggs, larvae (or nymphs), pupae and adults all have parasitoids.
How Do You Detect Parasitoids?
- Due to their modest size as adults and the fact that the majority of early-stage parasitoids spend most of their growth hidden within the host, people seldom ever notice them.
- Adults may be seen searching for plant hosts and checking their antennae, mouthparts, or ovipositors for potential insects by observant gardeners.
- Some parasitoid eggs or juvenile stages may be affixed to a host’s exterior, readily visible to the astute gardener. The parasitized tomato hornworm is a typical illustration.
- Many parasitoids leave the host to pupate, and their cocoons can be found on leaves of nearly dead prey or within host plants. But the most likely way to determine whether your garden is home to parasitoids is to look for indicators in the host insects.
- Even though parasitized hosts may seem secure for a time, there are indications that they are nearing the end.
Characteristic Symptoms of Parasitized Host Insects:
- When they are destroyed, when natural growth is impeded, or when the juvenile parasitoid inside is apparent through the host’s skin, hosts frequently change colour.
- Likewise, parasitized eggs may become significantly darker.
- The eggs, larvae, or pupae (cocoons) of ectoparasitoids may have distinctly complied with the outside of some hosts’ bodies.
- Mummified bodies swell and remain affixed to leaves due to their rigid exterior skin and hollowed-out core. Aphid mummies may occasionally turn black or brown, and soft-scale mummies may turn black.
- Exit holes left behind by newly emerging adult parasites are frequently found in the remains of dead hosts. In contrast to the rough, varying holes and shreds produced by predators, parasitoid emergence holes are often rounded and have rather smooth edges.
- Unusual host behaviour may point to parasitism: Some hosts relocate to another location from the region of the plant they frequently feed on, while others just stop feeding. Hosts continue to cling to plant leaves or stem, but they hardly ever move or take a sip.
- Their parasitoids make up the majority of insect parasitoids, but other significant ones include parasitized hornworms and white tachinid fly eggs on Japanese beetles, among others.
Dr. Kamran Saleem and Hafiz Muhammad Rizwan Mazhar
Nuclear Institute for Agriculture and Biology Faisalabad
