The Greatest Class of Animal

Why this title for the talk? Insects make up over 70 per cent of the approximately 1,260,000 described species in the Kingdom Animalia. What they lack in size they make up in numbers, mass and diversity (and sometimes beauty).

With this introduction Dr Brian Gunn went on to explain the co-evolution of insects and plants.

The insect fossil record begins around 400 million years ago (mya) but because of a poor fossil record insects, including winged insects, would have evolved earlier. Within 150 million years in the Carboniferous era (360-280 mya) several extant insect families (including mayflies, grasshoppers and dragonflies) were present. The Permian and Triassic eras (280-210 mya) saw a great diversification in insects and many of our extant insect families appeared in this period. Most modern families were represented in the Jurassic and Cretaceous periods as the conifer forests and flowering plants evolved. This included ants, bees, wasps and termites which developed to a greater or lesser extent a communal lifestyle.

Insects have survived the five mass extinction events since they evolved, in part because of their size and also because they have been able to benefit from the close co-evolution with plants.

Today 20 per cent of living insects depend on flowers, nectar and pollen while 65 per cent of flowering plants depend on insect pollination. This relationship is essential to maintain the health of the environment.

During the next part of the talk we learnt a lot about the insects themselves:

  • Insects have been able to establish themselves in almost every environment on Earth including icy climes of Antarctica (Springtails and Wingless midge) and the warm cinder cones of high volcanoes (Seed Bug).
  • The insects’ exoskeleton is composed of chitin (a derivative of glucose) and reinforced with sclerotin.
  • Insects can be divided into two major groups: Holometabola (including moths, butterflies, flies, bees, fleas and antlions) whose life cycle from egg to adult includes larval stages and pupal stages, and Hemimetabola (including bugs, grasshoppers, locusts, cockroaches, praying mantis, thrips and lice) who all go through a number of nymphal stages which resemble the adult. The Holometabola comprise around 80 per cent of all insect species, in part because the immature stages do not compete with the adults for resources as with the Hemimetabola.
  • In 2016 Australia had approximately 86,000 described species of insects, including 28,200 beetles, 20,816 butterflies and moths, 7,786 flies and mosquitoes, 4,000 ants and 2,827 grasshoppers and crickets.

In a section Brian labelled “The Diet Plan” we were reminded just how diverse the diet of insects is. All parts of plants are consumed- roots, tubers, stems, leaves, buds, flowers, fruits, seeds, nectar and sap while in the animal kingdom their diet may include skin, meat, blood, mucous, faeces, horns and hooves, and cadavers. Insects themselves do not escape as every gardener knows—predators and parasites can be very welcome visitors.

However, not all insects are that welcome. Insect-borne diseases have been devastating in the past: the Black Death (1348-1350), a disease carried by Oriental rat fleas on black rats, is estimated to have reduced Europe’s population by 30 per cent and today malaria is again on the rise. WHO estimated it was responsible for 440,000 deaths in 2015.

Brian concluded his talk with a discussion on insect societies, primarily a characteristic of ants, wasps, bees and termites who he termed “The Eusocial Set”. These insects are characterised by the reproductive division of labour, overlapping generations and co-operative care of the young. There are even members of a species of honey ant Myrmecocystus mexicanus who store honey within the body in case the colony cannot find enough food to feed all its members.

Pheromones are chemical messengers produced by insects and they rely on up to 100 pheromones to find food, mates and for aggregation within colonies. The pheromones are essential to regulate and maintain cohesion within insect societies.

It is the social set that can sometimes form ‘supercolonies’. Of 33 ant populations tested along the 6,004 kilometre (3,731 mile) stretch along the Mediterranean and Atlantic coasts in Southern Europe, 30 belonged to one supercolony, with estimated millions of nests and billions of workers, interspersed with three populations of another supercolony. The ant? The Argentinian ant! This ant is making a silent comeback in Western Australia so please be vigilant.

Don Poynton

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