Simply irresistible

The Grampians region of Victoria is one of Australia’s richest and most diverse flora areas. One third of Victoria’s flora is represented here so it is no surprise that the region was once dubbed “the Garden of Victoria” by the great botanist Ferdinand von Mueller.

Spring is an excellent time to see wildflowers throughout the region, especially terrestrial orchids such as the Mantis Orchid (Caladenia tentaculata) pictured below. It is one of the green-comb Spider Orchids and is common throughout the Grampians region. The colourful and flamboyant flowers of this orchid may be pleasing to the human eye but they are simply irresistible to certain male insects.

Caladenia tentaculata

The Mantis Orchid is one of many sexually deceptive orchids. Orchids such as these don’t have nectar to reward pollinating insects so they must attract insects some other way.  The orchids lure male insects to their flowers with scents that mimic female insect sex pheromones. The labellum of the flower where the male insect lands is hinged and swings the insect against the sexual organs of the flower. During its struggles to mate with the flower the insect will either pick up pollen, or deposit pollen that it has acquired from another flower.

The insect pollinator of the Mantis Orchid is a thynnine wasp of the family Tiphiidae. These wasps are the most important insects which pollinate Australian terrestrial orchids by pseudocopulation. The wasps are also remarkable because males are winged and females are wingless. A female wasp finds a mate by advertising her presence with pheromones, the male picks her up and mating occurs in flight. It is quite common to see mating pairs flying around our property. A mating pair of thynnine wasps is pictured below.

Thynnine wasps

All this flying around while mating means the wasps stay in a coupled position for a prolonged period of time. To facilitate this, both sexes have evolved unusually shaped genitalia that include spines, grooves and other structures, so that they don’t accidentally disengage. But why don’t the females have wings? Some female flower wasps are parasites of beetle larvae and mole crickets located underground. Winglessness allows females to dig underground and hunt for prey without risking damage to delicate wings. This probably sounds exotic and unusual, but wasps of the family Tiphiidae are common in Australia, in fact we have about 700 native species.

Thynnine wasps are not the only insects lured into pseudocopulation with native orchids. I think I have space for one more story which should be titled “How not to photograph a pseudocopulating insect“. One November some neighbours showed me Large Duck Orchids (Caleana major) flowering on their property. As you can see below they are spectacular flowers that resemble flying ducks, so I grabbed my camera for some shots.

Caleana major

Within minutes of me starting to shoot the orchids an insect arrived and landed on one of the flowers. “Holy cow”, I thought. “It’s the pollinator!” Heart racing I tried to capture the insect but in my excitement I tripped over my tripod and almost flattened the orchid! By the time I got myself organised the insect, a type of sawfly, was trapped inside the orchid and was barely visible. I did get a couple of shots of the insect emerging but they are pretty terrible (see below).

Duck Orchid pollinator

How did the orchid trap the insect? The ‘head’ of the duck is the lid of a trap which swings down by the ‘neck’ trapping the insect inside the ‘body’. In it’s struggles to escape the insect is covered with pollen and will transfer that to the next flowering Large Duck Orchid it is attracted to. Hopefully one day I can have another crack at these shots and try not to be overwhelmed by the occasion!

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Historic weevil

I first published this story back in April 2015. Recently, I spoke about this weevil on ABC Radio Ballarat and also at a talk I gave to Friends of the Grampians Gariwerd (FOGG) so I thought now is a good time to republish.

I found this fellow trundling along the road when I went for my morning walk the other day. This insect is commonly known as a Botany Bay weevil (Chrysolopus spectabilis) or by its other common name “diamond weevil”. This is the male of the species. Females are larger insects, making males the lesser of two weevils (sorry, I couldn’t resist!).

Botany Bay weevilBotany Bay weevils belong to an historic group of insects. This weevil was collected by Sir Joseph Banks on Captain James Cook’s voyage to Australia in 1770. Actually we don’t know that Banks himself collected it – it could have been one of his men, or the Swedish naturalist Daniel Solander who accompanied Banks on the voyage. On his return, Banks gave the task of cataloguing his insect collection to the Danish insect taxonomist Johann Fabricius. The weevil was described in 1775, making it one of the first (if not the first) Australian insects described to western science.

Sydneysiders may be surprised to learn that the Botany Bay weevil is not only found around Sydney, but from coastal far north Queensland to eastern South Australia. The weevil is certainly common in New South Wales and its common name probably dates back to the early colonial days of Botany Bay.

To this day we don’t actually know where Banks’ specimen was collected. Was the weevil collected at Botany Bay in April 1770, or during July/August 1770 when Cook was repairing the Endeavour near present day Cooktown, or at one of the other landing points in between? The label on the specimen simply says “nova Hollandia”.

Botany bay weevil femaleBotany Bay weevils are associated with about 30 species of Acacia. Female weevils chew holes in stems at or below ground level in which they lay their eggs. Upon hatching the larvae bore into the stem and usually down into the roots. Adult weevils emerge in the summer, and what spectacular insects they are with their rich metallic green or blue markings on a black background. The adult weevils also feed on Acacia spp. in their characteristic manner of removing the leading shoots several centimetres down the stem.

The Botany Bay weevil has a distinctive defence mechanism. One day I was taking some close-up images of weevils on Acacia provincialis when I got just a bit too close for comfort. The weevil suddenly went stiff, toppled backwards and fell to the ground like an actor in a B grade Western movie. The trick I learned was to move closer to them slowly, taking photos as I went, so they got used to me and the noise of the camera.

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Sap-suckers & sooty mould

Sooty mould is not a plant disease as such but various species of fungi, which grow on the sticky honeydew excreted by many species of sap-sucking insects. A very thick mould layer on leaves may cause a reduction in photosynthesis in plants, which can result in leaves falling prematurely. The main concern to gardeners (apart from the sap-sucking pests which caused it) is that a thick covering of sooty mould on a plant’s leaves is downright ugly.

Sooty mould is a serious problem for the horticultural industry. Ugly plants are unsaleable. Similarly in the citrus industry, the main economic damage caused by mealybugs is by the downgrading of fruit quality due to sooty mould growing on mealybug honeydew. The picture below shows a leaf infested by soft scale insects and the sooty mould they cause – pretty ugly eh?

Sooty mold

Insects which produce honeydew include planthoppers, leafhoppers, treehoppers, psyllids, whiteflies, aphids, scale insects and mealybugs – all ‘true bugs’ in the insect Order Hemiptera. These bugs consume vast quantities of watery sap from which they extract the nutrients they require, particularly nutrients containing nitrogen. Many kinds of sugars are also present in plant sap in abundance, which are not required by the insects and are excreted in solution as honeydew. Almost all the dry weight of honeydew is in the form of sugars. It’s worth tasting honeydew to experience just how sugary it is.

Many bugs propel the honeydew away from them so they don’t become trapped in the sticky stuff as it dries. The honeydew falls to foliage below, often in vast amounts when the insect colony is large. Wherever the honey dew falls sooty moulds may grow. The hibiscus leaf covered in sooty mould pictured below was directly below a leaf (underside) covered in greenhouse whitefly (Trialeurodes vaporariorum).

hibiscus sooty mold

But not all bugs throw their honeydew away. Some psyllids allow their honeydew to harden into protective ‘lerps’ (you can read more about them here) while other sap-sucking insects use honeydew to attract ants which act as their bodyguards. Such interaction between bugs and ants is known as trophobiosis and is based on reward (sweet honeydew) for services rendered (protection from predators). The relationship can be specific and involve a single ant species and a single bug species, or one ant species may interact with several species of bugs, or vice versa.

You don’t have to look far to find ants protecting honeydew producing bugs such as aphids, planthoppers and scale insects  – almost any park, garden, orchard or nursery will be harbouring such a relationship somewhere. The picture below shows some ants attending soft brown scale, and you can even see a drop of honey dew.

Anst feeding on honeydew

If ants are efficient at protecting the pest insects from predation such that pest numbers increase, ant control might be something you consider. For example, organic growers of citrus and other fruit have to use ant control as a means of controlling scale insects and other pests on their trees. To put it another way, controlling the ants gives predators and parasites a chance to control the pest insects. Ant control is simple – you can prevent the ants climbing a tree by banding the tree trunk with horticultural glue or some other sticky substance.

There are no fungicides registered against sooty mould – you must control the insect pests which produce the sticky honeydew on which the fungus grows. The fungus will stop growing once the honeydew source is removed, and will eventually dry out and fall off leaves, or it can be hosed off.

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It’s got 6 legs but it’s not an insect!

Q. When is an animal with six legs not an insect? A. When it’s an entognathous hexapod.

Until fairly recently it was thought that all animals with six legs were insects. It is now widely accepted that there are two classes of six-legged animals – the insects (class Insecta) and the entognathous hexapods (class Entognatha).

The Entognatha are six-legged animals characterized by mouthparts which are hidden away in a pouch in their head (entognathous). The insects (Insecta) have mouthparts which are not hidden (ectognathous).

HEXAPOD Noun. (Greek, hex = six + pous = foot.) Any 6-legged arthropod.
ENTOGNATHOUS Adj. (Greek, entos = within, inner + gnathos = jaw + Latin, –osus = with property of.) Hexapods with mouthparts recessed within head.
ECTOGNATHOUS Adj. (Greek, ektos = outside + gnathos = jaw + Latin, –osus = with property of.) An organism with protruding mouthparts.

The class Entognatha contains three orders: Collembola (springtails), Protura and Diplura. As well as recessed mouthparts these three orders have a few other things in common. They are all wingless (apterous). Also there is no visible change in form between the life cycle stages other than in size, meaning they don’t go through a process of metamorphosis and so are termed ‘ametabolous’.

The largest of these orders is Collembola, the springtails. There may be as many as 2000 species in Australia, many of them undescribed. They are called springtails because they have a prong at the tip of their abdomen (known as a furca) that is folded back like a spring. When released, the individual is launched into the air. You can see the furca in the image below. Springtails are usually tiny animals about 1mm to 3 mm long.

Collembola

Almost all springtails are considered beneficial species because they contribute to the breakdown of organic matter. There is one pest species in Australia and that is the so-called lucerne flea (Sminthuris viridis) which may damage emerging seedlings. Springtails don’t have eyes as such, instead they have a cluster of light sensing organs (known as ocelli) on each side of the head. You can see ocelli on the side of the head of the super cute springtail in the image below.

Springtail

Protura are rarely seen, tiny (< 2 mm long), pale, hexapods which may occur in soil, leaf litter, decaying wood and moss. There are about 30 described species in Australia. They have no eyes or antennae and hold their front legs forward apparently to feel their way around. Proturans were not described until 1907 and to this day very little is known about their behaviour. Some species have been observed feeding on mycorrhizal fungi, but it remains to be seen if all Proturans feed exclusively on mycorrhizal fungi. The line drawing below comes from CSIRO.

Protura

There are 31 described species in the order Diplura which occur in Australia. They vary greatly in form and size from pale delicate hexapods less than 5 mm in length to robust earwig-like species which may reach 50 mm in length. Diplurans have no eyes but do have a pair of antennae. They also have a pair of abdominal appendages known as cerci which are filamentous in the families Campodeidae and Projapygidae, but pincer-like in the families Japygidae, Heterojapygidae and Parajapygidae.

Diplurans of the families Campodeidae and Parajapygidae appear to be herbivorous, Projapygidae may be omnivorous, while the rest appear to be carnivorous. Heterojapyx (picture below) is certainly carnivorous. It waits buried in soil with only its pincers (forceps) above the surface, ready to grab any unsuspecting prey wandering by. Superficially it may resemble an earwig, but the lack of eyes and wings gives it away. I had never seen one of these in the flesh until recently when I stumbled upon one while chopping wood on my property. What a find!

Heterojapyx

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Preying on a mantis

For every insect out there, there is another insect which will try to eat it or breed in or on it.

Praying mantids are common predatory insects found in virtually any part of Australia in any habitat where they can find prey. Mantids are an insect Order all of their own known as Mantodea, comprising about 2,500 species worldwide, and about 200 Australian species. These insects are commonly called ‘mantises’ or singularly as a ‘mantis’ – but they are more correctly known as ‘mantids’ or singularly as a ‘mantid’.

Mantids are instantly recognisable insects with their triangular heads and their characteristic way of standing with forelegs held together as if they were praying – hence ‘praying’ mantid (image below). The word ‘mantis’ is derived from the Greek word for ‘seer’ or ‘prophet’, which probably alludes to their praying stance. There is a genus of mantids bearing the name Mantis – for example the classic ‘praying mantis’ Mantis religiosa found through Europe, Asia and Africa. Australia only has one representative of that genus, a mantid known as Mantis octospilota.

Praying mantid

Continue reading Preying on a mantis

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