Parasitoid Wasp Pupae on Tarbala Caterpillar

In the last blog I explained about Trabala Species of Lappet Moths. Few days back I found another Trabala caterpillar. This one was infested with pupae of Parasitoid wasps all over its body. It was lethargic and was unable to move.

In general though most people still use the term Parasitic Wasps. Technically speaking, they are not actually parasites – they are parasitoids. This is because a true parasite is something that lives at the expense of its host but doesn’t actually kill it, whereas parasitoids nearly always kill their host.

Parasitoid larvae usually develop by feeding on a single host – different species develop on anything from tiny aphids and insect eggs right up to large butterfly and moth larvae. They can live and feed inside the host’s body cavity (endoparasitoids) or outside the host’s body (ectoparasitoids). They can be solitary or gregarious – with anything from 1 to many 1000′s of larvae consuming the same host.

Parasitoid Wasp On Tarbala Closeup

Fascinating life strategies

Nearly all parasitica inject venom into their host along with or just prior to the egg. This venom is a highly complex mixture of chemicals and other agents used not just to paralyse the host, but to also modify the host’s tissues. Tissue modification is a feature of nearly all venoms, making the host more nutritious for the developing wasp larva and helping to overcome the host’s immune systems. The latter is an especially important consideration for internal parasitoids as a host’s body will usually try to surround (encapsulate) a foreign body to prevent infection and to kill any parasitoid eggs or larvae. Parasitica have developed many ways of getting around this but I think the most devious must be the use of polydnaviruses (also known as Poly-DNA-viruses) . These viruses are injected by some endoparasitoids with the venom and have been shown to target and disable the host’s immune system – thus protecting the developing parasitoid. Other, more basic, methods of bypassing the host’s immune system include laying the egg directly into the host’s brain (ganglion), where the immune system is unable to encapsulate it.

Whichever method the parasitoid uses to prevent encapsulation it must also protect itself against many other dangers. One of the most serious being the possibility that a host will succumb to a fungal or bacterial infection and die before the parasitoid has finished with it. To prevent this, many larvae secrete chemicals with antibiotic or antiseptic properties as they move around the host’s body cavity. They also avoid damaging the host’s gut (a massive source of bacteria) by eating non-essential areas first, like body fat and the reproductive organs. Many species also use teratocytes – bundles of cells that emerge from the egg with the embryo. These cells absorb food from the host’s body cavity and the parasitoid larva feeds on them – removing the need for it to feed directly on the host’s tissues until it is absolutely necessary.

Parasitoid Wasp Puape On Tarbala Caterpillar

Polyembryony is another complex strategy employed by parasitica, but this time its aim is to ensure the maximum number of offspring from the fewest number of eggs. Some species lay a single egg that continues to divide, cloning itself into many independent larvae – in extreme examples one egg can produce thousands of larvae. Some species have even been shown to produce different types of larvae from the same egg – normal larvae that feed and develop fully into adult wasps and others, which never mature into adult wasps, that act as guards to protect the others from attack by other parasitoid larvae.

Charles Darwin even used one family of Parasitoid wasps as evidence for natural selection, writing to a colleague:

I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars.

So what next turn will you see in the story of lappet moths, wait for my last installment on 3 part series on Lappet moths.

Final instar of Oleander Hawk Moth Caterpillar

Evening after the Photography workshop on 6th Dec 2009 I was tired from all the presentation and talk which happened at the workshop. Having taken bulk of the topics and over 8 sessions my throat was aching. We had 32 very nice enthusiastic youngsters who attended the workshop.The interaction was great and we all learned a lot about photography from each other. When I returned to my in-laws place at Bondel, Mangalore, I was eagerly greeted by my daughter who showed this plump green caterpillar which she sighted on the flowering bush in their garden. She had seen the similar caterpillar earlier at her school backyard and wanted to know the identification. There were 3 caterpillars on that Crape jasmine (Tabernaemontana divaricata) plant. They were caterpillars of the of the oleander hawk-moth.

Oleander Hawk Moth Caterpillar

The Oleander hawk-moth, Daphnis nerii (Linnaeus, 1758), one of the most widely distributed species of sphingid in the world, is known to occur in Africa, southern Europe, Arabia, Afghanistan, Pakistan, India, Sri Lanka, Myanmar, Nepal, Thailand, Yunnan (south China), Hong Kong, Taiwan, the Philippines, Sumatra, Peninsular Malaysia, and North Borneo, and has been introduced to southern Japan, Hawaii, and Guam. Its vernacular name refers to the oleander, Nerium oleander (family Apocynaceae), on which its larvae feed, among other members in its family of poisonous, laticiferous plants. Incidentally, the Oleander was also first described by renowned Swedish naturalist, Carolus Linnaeus in 1753. I had the great opportunity of photographing this moth earlier which I documented on this website here and here.

Defensive posture

Entire body of this caterpillar was a pleasant apple green, with a straight, dorso-lateral row of small, aqua-marine dots from its second to seventh abdominal segments, with a chalky white, longitudinal band immediately above this. There was also a scattering of distinct, white dots from its first to fifth abdominal segments. Its spiracles were jet black, outlined with white. On its third thoracic segment, there was a prominent pair of ocelli (A marking that resembles an eye), consisting of an outer, Dark Blue ring with a whitish blue center, clearly advertised when its defensive posture (head tucked under) was adopted.

Defensive pose of Oleander Hawk Moth Caterpillar

Its tail horn was relatively short and had a rounded tip. There was a sparse distribution of low, short spines over the entire tail horn, which was largely citrus-yellow. It was voraciously feeding on Crape jasmine leaves and excreting large greenish black pellets. Since it was dark we decided to visit and photograph it next day.

Next day morning when we went to visit the caterpillar again we just couldn’t find any apple green caterpillar. Previously apple-green body had transformed to a dirty orange on the flanks and an olive-brown on the dorsum. A symmetrical pair of round, black patches had also appeared on the top of its first thoracic segment, just posterior to its head.

Pre Pupal stage of Oleander Hawk Moth Caterpillar

The thick rings of its false eye spots had darkened to a black outline. The yellow of its posterior tail horn had now darker orange. This was pre-pupal metamorphosis of the caterpillar. What we saw yesterday was the final instar version of this caterpillar.As we were observing the caterpillar was descending to the ground. Then it dropped to the ground and started burrowing deep into the soil to pupate. I did not disturb its path and let it continue. In another 10days I was sure it is going to emerge out of its pupa and brilliantly colored oleander hawk moth which I had previously documented on my website.

Pre-Pupal Stage of Oleander Hawk-Moth Caterpillar

Descriptions and illustrations of the larva and pupa of the oleander hawk-moth were provided previously by Bell & Scott (1937), with more recent works by Pittaway (1993) and Pittaway & Kitching (2009). Throughout its broad geographical distribution, the combined list of documented larval host plants for the oleander hawk-moth comprises no fewer than 32 genera in 12 families, clear indications of a polyphagous diet. However, there appears to be a strong preference for plants in the family Apocynaceae, with at least 17 genera (more than half) recorded. A most probable advantage of consuming potentially poisonous plants in this family would be the chemical defense that the larvae would be able to derive from them. For example, the leaves and other parts of the oleander contain a potent concoction of cardiac glycosides (cardenolides), such as oleandrin, which can cause nausea, vomiting, weakness, irregular pulse and decreased heart rate. The oleander has even been responsible for occasional fatalities in humans. Thus the plants in the Apocynaceae would confer the larvae considerable deterrence against a variety of predators.

Reference

• Beck, J. & I. J. Kitching, 2008. The Sphingidae of Southeast-Asia (incl. New Guinea, Bismarck & Solomon Islands).Version 1.5. http://www.sphin-sea.unibas.ch/.
• Bell, T. R. D. & F. B. Scott, 1937. The Fauna of British India, including Ceylon and Burma. Moths. Volume V. Sphingidae. London.
• Inoue, H., R. D. Kennett & I. J. Kitching, 1997. Moths of Thailand, Volume Two Sphingidae. Chok Chai Press, Bangkok.
• Jarvis, C., 2009. The Linnaean Plant Name Typification Project. The Natural History Museum, London. http://www.nhm.ac.uk/research-curation/research/projects/linnaean-typification/.
• Pittaway, A. R., 1993. The Hawkmoths of the Western Palaearctic. Harley Books, in association with the Natural History Museum (London), Essex.
• Pittaway, A. R. & I. J. Kitching, 2009. Sphingidae of the Eastern Palaearctic. http://tpittaway.tripod.com/china/china.htm
• Robinson, G. S., P. R. Ackery, I. J. Kitchi HOSTSA Database of the The Natural History Museum, London. http://www.nhm.ac.uk/research-curation/research/projects/hostplants/
• Stewart, A., 2009. Wicked plants. Algonquin Books of Chapel Hill, North Carolina.
• van Wyk, B.-E. & M. Wink, 2004. Medicinal Plants of the WorldAn Illustrated Scientific Guide to Important Medicinal Plants and Their Uses. Times Editions-Marshall Cavendish, Singapore.
• Wasfi, I. A., O. Zorob, N. A. Al Katheeri & A. M. Al Awadhi, 2008. A fatal case of oleandrin poisoning. Forensic Science International.
• Wee, Y. C., 2005. Plants that Heal, Thrill and Kill. SNP International, Singapore.

Dried Foxglove

It was an overcast evening. Tropical cyclone 4A was getting intensified in the coast. I was tired after trying to cajole a rat snake (Ptyas mucosus) to give nice pose to my camera. It was busy hunting and did not give provide any good photos. I did not want to disturb its hunger. Then I saw this Foxglove plant all dried and thorny. Here are 2 photos taken using Canon EF 100mm f/2.8L Macro IS USM on my Canon EOS 5D mark II using Canon Speedlite 580EX II with Lumiquest Clone diffuser. For the shot above I used F/11 and 200th of second exposure thus throwing the background dark. This is the same technique where you want the object in focus will brightly lit, highlighted and background will be dark and does not distract the viewer.

Foxglove

For the second shot I wanted the background to show. Canon EF 100mm f/2.8L Macro IS USM Produces a very nice bokeh effect and thus the creamy background will not distract the foreground object. Since the light was low, I used same setup and flash but changed the aperture to F/4 and speed to 40th of second. This setup allows background to show thus resulting in a pleasing result. Fill flash illuminated the object and made it to stand out from the background. F/4 resulted in a very shallow depth of field. So I had to step back to get sufficient parts of the plant in focus.

Digitalis purpurea Common Foxglove, Purple Foxglove or Lady’s Glove, is a flowering plant in the family Plantaginaceae (formerly treated in the family Scrophulariaceae). Due to the presence of the cardiac glycoside digitoxin, the leaves, flowers and seeds of this plant are all poisonous to humans and some animals and can be fatal if eaten.

Extracted from the leaves, this same compound, whose clinical use was pioneered as digitalis by William Withering, is used as a medication for heart failure. He recognized that it reduced dropsy, increased urine flow and had a powerful effect on the heart. Unlike the purified pharmacological forms, extracts of this plant didn’t frequently cause intoxication because they induced nausea and vomiting within minutes of ingestion, preventing the patient from consuming more.