How do these vampires grow?

The general life cycle of a parasitoid involves laying eggs in/on the host, wherein the egg hatch into a larva and starts feeding on the host. The larva continues to grow at the expense of the host. The mature larva leaves the now dead host and forms a pupa. Adults emerge from the pupae, they feed on pollen and nectar of flowers. The mature individual’s mate and then attack a new host. Every step in this cycle (Figure 1) varies from species to species. Some parasitoids attack one or two hosts others may attack many. Their size varies from very minute fairy wasps/fairy flies (less than 1mm, lays eggs in eggs of other insects) to very large Giant Ichneumon wasps (up to 16cm, have large ovipositors). The best time to look out for them is the time when their hosts are abundant, i.e., the onset of monsoon and spring seasons, on vegetation in your backyard, or to keep an eye on their host caterpillars for infected ones.

The success and survival of an individual parasitoid depend upon its ability to find a suitable host and attack the appropriate life stage. A parasitoid locates its host in three ways, Signals produced by the host (faeces); signals from the host's microhabitat/home (plant volatiles from the host-food plant); and the signals that are produced due to the activity of the host in the microhabitat (broken leaves produce scents).

The shiny devil

Strikingly elegant emerald cockroach wasp (Ampulex compressa), aptly called as the Jewel Wasp is otherwise a cunning cockroach hunter. It attacks cockroaches and leave it for their young to feed. After mating it search for a cockroach and stalks it like a tiger. After closing onto the cockroach, she stings and injects venom into the brain. The venom stupefies the cockroach so that it doesn’t fight back, but simply follows the wasp to its doom in the same way we were dragged to school as kids- unwillingly. The wasp then lays an egg on the leg of the cockroach and seals the burrow entrance.

A small larva hatch after 3 days and feed on the organs of cockroach and eventually killing it, in the same way as the beetles eat people from inside in the ‘The Mummy’ movie. After feeding the larvae pupates and emerges as a beautiful jewel wasp from the cockroach’s corpse, with the whole cycle taking from 10-16 days from the day the egg is laid.

Are parasitoids bad?

It will be like not giving a hero his credit of being a hero. As seen in the case of jewel wasp which kills cockroach, they save a lot of our money by eliminating the need of using Hit or Lakshman Rekha (Anti roach sprays and gels). Not only cockroaches, parasitoids kill other insects that are harmful to our crops like Potato tuber moth, sugarcane top borer, aphids, and beetles which destroy a lot of food and leave many hungry. They are an important component of biological control of agricultural pests especially of food crops like rice, wheat, sugarcane thereby reducing the impact of chemical fertilizers on friendly insects and the environment. So, the answer lies in front of you that they are not bad at all but quite useful to us, not all vampires are bad you will know if you have watched ‘Hotel Transylvania’ movie.

So, given their helpful nature in controlling other insects, they became favorites of many agricultural scientists. But they have been also used to investigate the evolution of sex ratios and reproductive behavior by ecologists.

Insects are found almost everywhere and all we need a little effort to know more about them. I am telling you; this will be a great way of stressbuster in this period of lockdown. Although there are very few resources about insects in India, you can use online platforms like iNaturalist, knowyourinsects.org for identification, and exploring about insects. Never wonder one day if we keep our search, we may find a parasitoid that might control the populations of the highly feared locusts that have estimated to have caused a loss of Rs 100 crore in current cropping season in India. Do keep an eye on these small creatures in your backyard this monsoon.

“If we were to wipe out insects alone on this planet, the rest of life and humanity with it would mostly disappear from the land. Within a few months.” E. O. Wilson

Further reading

• Godfray, H. C. J., & Godfray, H. (1994). Parasitoids: behavioral and evolutionary ecology (Vol. 67). Princeton University Press.

References

• Arvidson, R., Landa, V., Frankenberg, S., & Adams, M. E. (2018). Life History of the Emerald Jewel Wasp Ampulex compressa. Journal of Hymenoptera Research, 63, 1– 13. doi: 10.3897/jhr.63.21762

• Eggleton, P., & Gaston, K. J. (1990). “ Parasitoid” species and assemblages: convenient definitions or misleading compromises? Oikos, 417–421.

• Lafferty, K. D., & Kuris, A. M. (2002). Trophic strategies, animal diversity and body size. Trends in Ecology & Evolution, 17(11), 507–513. doi: 10.1016/S0169- 5347(02)02615-0

• Sandhya Ramesh. (2020, May 29). Why the worst locust attack in decades has invaded north India. Retrieved July 4, 2020, from ThePrint website:

• Sathe, T. V. (2003). Indian Pest Parasitoids. Daya Books.

• Tanaka, C., Kainoh, Y., & Honda, H. (2001). Host frass as arrestant chemicals in locating host Mythimna separata by the tachinid fly Exorista japonica. Entomologia Experimentalis et Applicata, 100(2), 173–178