World of insects

Print edition : August 12, 2011

Insects are a successful and highly evolved group of animals whose lineage pre-dates dinosaurs.

THE author Sir Arthur Conan Doyle wrote, Clouds of insects danced and buzzed in the golden autumn light.... Long, glinting dragonflies shot across the path, or hung tremulous with gauzy wings and gleaming bodies. Contrast this with these words from J.K Rowling's Harry Potter and the Deathly Hallows, His voice cracked with the strain, and they stood looking at each other in the whiteness and the emptiness, and Harry felt they were as insignificant as insects beneath the wide sky, and you have the cultural evolution of humans in a nutshell. Insignificant is how modern humans see insects. Is it a sign of ignorance or a testimony to the increasing distance between nature and humans? Do insects deserve this prejudice?

AN ATLAS MOTH, which is Asia's largest moth.-

As Archy the cockroach wittily remarked: 1 i do not see why men should be so proud insects have the more ancient lineage according to the scientists insects were insects when man was only a burbling whatisit

THE INSECT'S WINGS are an extension of its cuticle with little support of or association with powerful muscles. (Above) a tiger moth.-

What can be said of insects that one has not already heard? Plenty! It is a story of more than 400 million years of evolution that is seldom told and, therefore, one is often left with the preconceived, mixed notion of the insignificance, usefulness and harmfulness of insects. Useful or harmful is a concept that can be applied to any entity, living or non-living. Why single out insects when this is true of human beings too? So let us look beyond this traditional viewpoint. Let us focus instead on insects as they are, for what they are a successful and highly evolved group of animals whose lineage pre-dates dinosaurs and who probably made their grand entry on this planet when the fish were holding centre stage.

A cow bug.-

While other organisms have appeared on and disappeared from the earth, insects have remained. What made this possible? What made the insect tick for millions of years through changing climates and conditions while other creatures succumbed to the vicissitudes of nature and became extinct? The answer lies in the insect's vast genetic diversity due to its long evolutionary lineage, which allowed its progeny/descendants to fill up almost every corner of the earth.

WASPS, ANTS, APHIDS, scale insects, certain flies, beetles and a whole variety of bugs change the way they reproduce and even the gender of their offspring in response to fluctuating environmental conditions.-

Their arrival on earth

THE ADULT MAYFLY has a short lifespan ranging from a few hours to a day.-

Four hundred million years ago, in an age described by palaeontologists as the Age of Fishes, insects appeared. While a million or more insects are to be found today, their past diversity is considered to be of a much larger magnitude. Similarly, the large insects of today, such as the goliath beetle or the sphinx moth, are dwarfs compared with their prehistoric counterparts. Odonata (dragonfly) fossils from the Palaeozoic era show wingspans of 55 centimetres. This is because prehistoric insects lived at a time when the oxygen content of the air was around 32 per cent. This meant they had a higher metabolic rate and more energy, which facilitated large sizes. As environmental conditions changed and oxygen concentrations dwindled (it is now only 21 per cent), insects adapted to the hypoxic environment by reducing their size. The fossil record from excavations at Burgess Shale in the Canadian Rockies tells a tale of insect forms that is worthy of any blockbuster sci-fi bug movie.

A DRAGONFLY. HOW the flight and wings of insects originated is still a hotly debated topic.-

Then came flight

INSECTS ARE NOT fussy about their food. From dung to chocolates, syrupy nectars to blood and dust, leftover food to fresh fruits, they accept any offering with pleasure. Here, a common nawab butterfly feeding on a dead fish.-

Why did the ability to fly develop? Was it for basking, hopping, jumping, sexual display, paragliding, surface sailing? 2 Whatever the reason, the evolution of actively powered flight was a critical component to the continued success and survival of insects. A Zen narrative offers an intuitive reflection of this defining event 3:

A PRAYING MANTIS. "The Mantis, I fear, has no heart. She eats her husband and deserts her children," wrote Jean Henri Fabre.-

Go to the edge, the voice said. No! they said, we will fall. Go to the edge, the voice said. No! they said, we will be pushed over. Go to the edge, the voice said. So they went... and they were pushed... and they flew...

A COCKCHAFER BEETLE.-

Insect wings are quite different from the wings of birds or bats, where limbs have a close association with the wings. The insect's wings are an extension of its cuticle with little support of or association with powerful muscles. Flight is a costly activity in terms of energy expenditure. Insects breathe oxygen directly into their body parts through openings called spiracles. This dictates the evolution of all their morphological features. How flight and wings originated is still a hotly debated topic. Was there a proto-wing that originated from a part of a leg of an ancestral species? Could this structure attain the size needed to support active flight? Would that size account for the aerodynamics of flight? What were the pressures on insects to increase wing size from the prototype?

A chrysomelid beetle. In some beetles, the adult and its larval grub both feed on plants, but one eats only the stem while the other eats only the root.-

There are several hypotheses. One, based on observations of butterflies basking in the sun, holds that the expansion of wing size had nothing to do with flight. Wingspan increased to serve the purpose of thermoregulation or sexual displays rather than active flight. A second hypothesis states that the prototypes had an aerodynamic function that was more in tune with movements such as a quick descent by paragliding, jumping/hopping to cover longer distances to escape predators, and surface sailing and/or floating to skim across water surfaces. The last word on the subject is yet to be heard. The next time you see a butterfly sail past or a hoverfly hovering or watch the antics of a dragonfly, remember the story is far from over. Insects are sure to have a trick or two still up their sleeves, or should I say wings!

Resource use

I asked a leading entomologist whether collecting insects for study would lead to their extinction. His answer merits reflection. He and other entomologists of repute believe that insects cannot be pushed to extinction by collection. The threat of extinction, if any, comes from habitat destruction.4 Why does collection not destroy their numbers?

BRACONID WASP LARVAE growing on a caterpillar, which acts as a food source.-

The secret lies in their number game, which appears superficially simple in overall design but is complex in details and involves several issues. There must be sufficient food resources to sustain large populations. However, the game becomes complex because for insect populations to be maintained, several other factors in addition to food need to be synchronised and that too within the insects' short lifespans. So what happens when resources fluctuate? Insects have addressed the problem in an evolutionarily sophisticated manner, adopting multiple strategies to fine-tune complex physiological responses to fluctuations in the external environment.

A LEAF KATYDID. Insects changed and adapted, diversified, and grew in size, form and function.-

Insects have done a remarkable job of utilising their resources to maximise their numbers. They are not fussy about their food. From dung to chocolates, syrupy nectars to blood and dust, leftover food to fresh fruits, they accept any offering with pleasure. They not only feed on these offerings but store and share them, modify them to their taste and needs, and sometimes use them as nests for their offspring. Such versatility! What is more, they even eat their own as well as other insect species. Insects are both predators and prey, and this serves to check their population growth.

IN SEVERAL SPECIES of moths - for example, the tussar silk moth, the atlas moth.-

For instance, adult insects and their young ones do not share the same food source. This a very simple strategy. Potter wasps leave food for their developing larvae in the form of paralysed, live caterpillars or spiders, while they feed on other sources. In some beetles, the adult and its larval grub both feed on plants, but one eats only the stem while the other eats only the root. The caterpillar does not eat what the butterflies or moths feed on.

The luna moth - the adults do not feed at all. Their job is to mate and lay eggs.-

Moths are a step ahead of butterflies: in several species of moths, the adults do not feed at all; they have no mouth parts and digestive systems. The adult atlas moth, Asia's largest moth, lives for a mere week, during which time it must mate and lay eggs. Its feeding time is when it is a caterpillar. The energy accumulated at this stage provides not only for the metamorphosis into the pupa and adult stages but also for sustaining the adult form until it mates and lays eggs. Could this be a reason for the number of moth species far outstripping the number of butterfly species worldwide? Do not grudge the caterpillar its leaves the next time you see it feed. Anthropocentrically speaking, moth caterpillars redefine the meaning of parent.

Reproduction

The pinnacle of success can be attributed to the strategies adopted for reproduction. Several insect communities have and/or can produce homosexuals, bisexuals, hermaphrodites and, of course, males and females. Some species, in response to environmental factors, decide whether the larvae metamorphose into adults or remain as larvae. In several species, the female has the last word in reproduction; the male must comply or perish.

DUNG BEETLES FEED on dung and use a ball of dung as a nest for their offspring.-

While the predominant mode of reproduction is sexual, several factors can alter this process. So wasps, ants, aphids, scale insects, certain flies, beetles and a whole variety of homopterans (bugs) will not only change the way they reproduce but even alter the gender of their offspring. Many insects have even dispensed with the process of mating. For instance, in response to fluctuating environmental conditions, aphids vary the sex of the egg produced, and mix parthenogenetic (a type of asexual reproduction) and sexual cycles according to season.

THE MALES OF the giant water bugs are caring fathers who carry the eggs on their backs until they hatch.-

There are also insects that never reach the adult stage at all. In gall midges, for instance, the future course of female larvae is dictated by environmental conditions. These larvae can metamorphose into female adults or simply produce more larvae by a process called paedogenesis. The newly formed larvae can be females, males or both. For the male larvae, there is only the one option grow into an adult. This is a well-evolved strategy to take advantage of the available food in the environment.

A REDUVIID BUG. Ancient peoples viewed, and many present-day tribal communities still view, insects with compassion and understanding.-

Reproductive behaviours, which seem strange from the human viewpoint, are common in the insect world. Their bizarre behaviours are often associated with issues of nutrition. Certain beetles mate when they are in dire need of water. The female's reproductive tract reabsorbs the water from the male's ejaculate. The Mantis, I fear, has no heart. She eats her husband and deserts her children, wrote Jean Henri Fabre. Research has shown that female praying mantises cannibalise males after or during mating to overcome nutritional deprivations, and a meal of their partner seems to result in significantly larger egg cases. A case of wholesome investment.

But not everything is so strange. There are caring males and females too. The entire structure of social insects revolves around a caring and cared-for female. However, in the family of water bugs, the males are the caring parents. The males of the giant water bug, which feeds on vertebrates such as fish and tadpoles, are gentle, caring fathers who carry the eggs on their backs until they hatch. Their parental care is very touching, for they even risk predation in ensuring that their eggs do not desiccate.

MANY INSECTS ARE brilliantly patterned (like the geometrid moth).-

The brilliant colours and patterns of jewel beetles, butterflies, moths, and wasps; the fantastic architecture of termites; the myriad sounds of crickets and bugs; insects' tenacity, patience and physiology these are stories that have to be told some other time.

Brilliantly coloured (like the ladybird beetle).-

As ice age followed ice age, as extinctions came and went, the insects ploughed on. They changed and adapted, diversified, and grew in size, form and function to occupy every niche available on the planet. The ancestral cockroach watched the arrival and departure of Australopithecines and witnessed the evolution of homo sapiens. Ancient humans watched them, understood their success and significance, took care of them and worshipped them. Modern humans, out of sync with nature and ignorant of the value of insects, squash, swat and spray them, and pray that they go away. But never once do they stop to reflect that it is possible to meet insects in a totally different way, just as the ancient Egyptians, Chinese, Indians or Mesopotamians did or as many tribal communities continue to do, with compassion and understanding.

AMATA PASSALIS MOTHS mating. The predominant mode of insect reproduction is sexual, but several factors can alter this process.-

Geetha Iyer is an author, a nature enthusiast and an independent consultant in the fields of environment and education.

REFERENCES

1. Marquis, Don; certain maxims of archy in archy and mehitabel' (1927); https://www.donmarquis.com/ readingroom/archybooks/ maxims.html

2. Gullan, P.J. and Cranston, P.S.; The Insects: An Outline of Entomology' (2005); Department of Entomology, University of California, Davis, U.S.; Blackwell Publishing Ltd.

3. Lauck, Joanne Elizabeth; The VOICE of the INFINITE in the SMALL: Re-Visioning the Insect-Human Connection' (2002); Shambhala Publications, Inc., Boston & London; page 205.

4. Gullan, P.J. and Cranston, P.S.; The Insects: An Outline of Entomology' (2005); Department of Entomology, University of California, Davis, U.S.; Blackwell Publishing Ltd; page 16 (Collected to extinction).

Habitat protection: https://archive.constantcontact.com

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