Parasitoid Wasp’s Pupae on Trabala Caterpillar: “The Enemy of My Enemy Is My Friend”

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I once conducted a study on the Trabala caterpillar’s non-mutual symbiotic relationship or parasitism, which is located and found in Bukit Lawang Hill Resort, North Sumatra, Indonesia, at an altitude of 312 meters above sea level.

Because plants have mobility limitations, they must devise a defense strategy to protect themselves when attacked by herbivorous insects. When herbivorous insects such as caterpillars eat their leaves, the wound on the leaf will stimulate a transduction signal to produce volatile compounds such as terpenoids.

These compounds will evaporate into the air, attracting predatory or parasitoid insects that will seek out caterpillars as live hosts to lay their eggs; this is what we call parasitism at work in the Leuser ecosystem. In addition, other volatile compounds will also be responded to by other plants as a form of indirect resistance to other herbivores and insects that may attack them.

“I would love to say the tale of this extraordinary biological process could be titled “The Enemy of My Enemy Will Kill My Enemy.” That’s how we should say it!” Bobi Handoko.

trabala caterpillar

An observed Trabala caterpillar in the picture, which has been infested with pupae of Cotesia flavipes was found in the Bukit Lawang Hill Resort garden. Parasitoid larvae develop by feeding on their host’s body. The parasitoid phenomenon in this case is a common thing that happens between Trabala pallida and Cotesia flavipes and is also known as natural selection.

Technically speaking, this parasite is categorized as an endoparasitoid because the parasites live and feed on the host’s body until the host dies. Cotesia flavipes is a species complex that is always found in biological pest control processes. In my observation area, I saw Cotesia flavipes flying several times.

parasitized trabala

The picture above shows a dead Trabala three weeks after being parasitized by Cotesia flavipes. The young wasps will hatch from eggs 12 to 16 days after oviposition; they fly about 4 days later.

It has also been observed that this process is extremely vulnerable to the birds that may feed on them due to the spread of volatile compounds such as terpenoids, for which a long evolutionary process has trained birds to recognize the spread of these compounds in the air.

The last picture is a 4-day-old Cotesia flavipes. Some young will keep feeding on the dead body of the Trabala caterpillar until they are stable and strong enough to fly to start their lives. The young Cotesia flavipes are very vulnerable to other animals that are always ready to hunt them, such as jumping spiders and other predatory insects.

cotesia flavipes

There are many species of parasitoid wasps worldwide, especially in Sumatra, most of them are so tiny that they are rarely noticed by our eyes. They’re categorized as a group that may be the single most important biological control method gardeners have. Furthermore, their existence shares important roles in the fruit season in a large area.

Trabala caterpillars that successfully metamorphose will grow into moths, as shown in the picture below. They are considered parasites for plants in the caterpillar phase; after they metamorphose into moths, they will serve to pollinate at night.

trabala moth

The colorful things in a moth or butterfly are formations of thousands of microscopic scales that provide rigidity to the wings that allow them to fly. Besides that, these colorful scales also serve as a warning sign to predators or as a tool for communication with other moths. Colors are important for moths; moths use color to see flowers at night. Moths lose the colorful scales on their wings with age; the more of these scales they lose, the less maneuverable they are and the less effective their eye spots are. This will also be followed by the end of their service as night shift pollinators.

References: Sharma, E. Anand, G. Kapoor, (2017). Terpenoids in plant and arbuscular mycorrhiza-reinforced defense against herbivorous insects. Annals of Botany, MCW263.

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