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DISPLAYING POSTS TAGGED: bug of the month (19)

More on the Monarch

Author
by Patrick
Publish date
20 March 2013
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Comments (3)

The Wanderer Butterfly, or Monarch, is probably the most recognisable butterfly in the world. It populates children's books and is the classical species used to illustrate insect life cycles. The Children's Museum at Melbourne Museum has housed enormous replicas of the Wanderer caterpillar, pupa and adult for the last 13 years.

Butterfly models in museum The giant butterfly, pupa and caterpillar in the Children's Gallery at Melbourne Museum.
Image: Patrick Honan
Source: Museum Victoria
 

Wanderer caterpillars feed on plants known as milkweeds. In Australia these include plants introduced from Africa and South America, such as Asclepias and Gomphocarpus. One of the most common is the Swan Plant (Gomphocarpus fruticosa), which may have been accidentally introduced as part of the regular trade between Australia and South Africa, or deliberately introduced for the 'silk cotton' to assist in hat making. This species is considered a noxious weed in some parts of Australia, and its abundance has been dramatically reduced by weed control programs, leading to a concurrent reduction in Wanderer populations around Melbourne.

Caterpillars feeding Caterpillars feeding on the Swan Palnt, Gomphocarpus fruticosa.
Source: Patrick Honan
 

Milkweeds contain poisons called cardiac glycosides which are absorbed by the caterpillars and used for their own defences. These poisons affect the hearts of vertebrates such as birds, inducing vomiting at half the lethal dose. Wanderers advertise the fact that they are poisonous to eat with contrasting patterns of yellow and black in the caterpillar, and orange and black in the adult. The chemicals are concentrated in the tips of the wings of adults, so any bird venturing a taste will cop a full dose and leave the butterfly alone.

Wing of butterfly. The warning colours on the hindwing of a Wanderer Butterfly. The black spot is the 'sex gland' of a male.
Source: Patrick Honan
 

The caterpillars themselves also become victims of their own food plants. Studies in the USA show that up to 30 per cent of very young caterpillars become glued to the leaves of milkweeds by latex in the sticky sap. And when its first bite ingests an unusually high quantity of cardiac glycosides, a newly-hatched caterpillar may become seized for ten minutes or more in a state of catalepsis before recovering.

Caterpillar feeding A late-instar caterpillar addressing the milky sap of Asclepias rotundifolia.
Source: Patrick Honan
 

Despite this, some birds such as Pied Currawongs (Strepera graculina) and Black-faced Cuckoo-shrikes (Coracina novaehollandiae) seem to be able to feed on Wanderers with impunity. The caterpillars are also attacked by a tachinid fly (Winthemia neowinthemoides), whose larvae feed on caterpillars from the inside, slowly killing them. In some areas, particularly coastal NSW and Queensland, these parasites account for 80-100 per cent of Wanderer larvae.

mating butterflies A male Wanderer overpowers the female (left) before flying off together and resting for several hours whilst mating (right).
Source: Patrick Honan
 

Mating by Wanderer Butterflies can be an aggressive experience. Males patrol patches of host plants, awaiting females. When females appear they are chased with great vigour by the males, often spiralling high into the air. Eventually the male may overpower her with the assistance of pheromones that cause her wing muscles to seize, forcing her to the ground where he mates with her. In Australia, breeding may occur year-round in the northern parts of the Wanderers' range, but in southern areas thousands of adults cluster together in trees after mating to see out the cooler months. Although not as spectacular as the roosting sites in North America that host many millions of butterflies, these clusters around Sydney and Adelaide are a memorable sight.

Female Wanderer Butterfly Female Wanderer resting during the day.
Source: Patrick Honan
 

Flight of the Butterflies 3D opens at IMAX Melbourne Museum on 21 March. 

Patrick's first post: Monarch or Wanderer butterfly

 

References

Orr, A. & Kitching, R., 2010, The Butterflies of Australia, Allen & Unwin, Sydney, 296pp.

Oyeyele, S.O & Zalucki, M.P., 1990, Cardiac glycosides and oviposition by Danaus plexippus on Asclepias fruticosa in south-east Queensland (Australia), with notes on the effect of plant nitrogen content, Ecological Entomology, 15:177–185.

Parsons, W.T. & Cuthbertson, E.G., 2001, Noxious Weeds of Australia, CSIRO Publishing, Melbourne, 698pp

Zalucki, M.P. & Brower, L.P., 1992, Survival of first instar larvae of Danaus plexippus (Lepidoptera: Danainae) in relation to cardiac glycoside and latex content of Asclepias humistrata (Asclepiadaceae), Chemoecology, 3(2):81-93

Wanderer or Monarch butterfly

Author
by Patrick
Publish date
8 March 2013
Comments
Comments (7)

The Wanderer Butterfly is known overseas as the Monarch Butterfly, so named for being the King, or Queen, of butterflies. In North America they are also known as King Billies, after William of Orange. The Australian name of Wanderer comes from its remarkable habit of long distance migration. The scientific name Danaus plexippus was bestowed by Carolus Linnaeus, the father of taxonomy and inventor of the scientific naming system.

Adult female Wanderer Butterfly Adult female Wanderer Butterfly
Source: Patrick Honan
 

Although not a native to Australia, the Wanderer may not exactly be introduced in the usual sense. Wanderer Butterflies most likely arrived in Australia across the Coral Sea from Vanuatu or New Caledonia, carried by three cyclones in early 1870. This was part of a major expansion in distribution across the Pacific and Atlantic Oceans from North America in the late 1800s, probably due to a combination of environmental factors, human movement and natural expansion.

Wanderer butterfly feeding An adult Wanderer Butterfly feeding on Cat's Whiskers (Orthopsiphon aristatus).
Source: Patrick Honan
 

The first recorded observations from Australia were made in February 1871 in Queensland, followed by the first record from Melbourne in April 1872. It is possible that Wanderers had been making the journey to Australia since time immemorial, but only after Europeans established their food plants here could Wanderers establish.

Wanderer caterpillar The distinctive fleshy 'filaments' behind the head of the caterpillar are used as sensory organs.
Source: Patrick Honan
 

Wanderers have been seen at sea up to 500km from land and occasionally settle on passing ships. This is not unusual – with favourable winds, Australian butterflies such as Common Eggflies often end up in New Zealand. Wanderers have a cruising speed of about 30km per hour with bursts of up to 50km per hour when alarmed.

Wanderer Butterfly pupa. The wings of the adult can be seen through the walls of a Wanderer Butterfly pupa.
Source: Patrick Honan
 

In North America, Wanderers undertake a famous annual migration from Canada and northern USA down to Mexico and California, and then back again. The populations overwintering in the Oyamel Fir Forests of Mexico roost at densities of 10 million butterflies per hectare. Because the length of time required for the migration exceeds that of an adult Wanderer's life span, those arriving back in Canada are the descendents of those that left the year before.

Map of butterfly migration Map of the North American migration of the Monarch or Wanderer butterfly that occurs each year in autumn.
Source: Via the Frost Lab, Queen's University Department of Psychology
 

The secrets of the Wanderer migration in North America weren't fully revealed until the 1970s. Canadian Dr Fred Urquhart was fascinated as a child by the question of where all the Wanderers disappeared to during winter, and he and his team of volunteers took nearly 40 years to discover the answer. Professor Urquhart died in 2002 but his life-long search is the subject of the new film Flight of the Butterflies 3D. In Australia, Dr Courtenay Smithers from the Australian Museum began tagging Wanderer Butterflies in the 1970s using many volunteers from the broader community. His studies revealed that overwintering populations around Sydney and Adelaide move into Melbourne and surrounds during summer. This research continues, with many questions still to be answered. In certain years, for example, populations appear to overwinter in some parts of Victoria, such as Phillip Island and the Western Districts, without needing to move interstate, but more data is needed to confirm these observations.

Flight of the Butterflies 3D opens at IMAX Melbourne Museum on 21 March. 

Patrick's next post on these butterflies: More on the Monarch

References:

Clake, A.R. & Zalucki, M.P., 2004. Monarchs in Australia: On the Winds of A Storm? Biological Invasions, 6:123-127

McCubbin, C., 1970, Australian Butterflies, Thomas Nelson Ltd, Melbourne, 206pp.

Bug of the Month - the mosquito

Author
by Tim Blackburn
Publish date
4 February 2013
Comments
Comments (2)

Mosquitoes are midge-like flies comprising the family Cucilidae. There are over 3,500 species of mosquito described worldwide and most of these require vertebrate blood as the principal portion of the female diet. The blood provides protein for egg development and maturation, and the lipids it contains are an energy source. Females possess elongated piercing and sucking mouthparts for obtaining their blood meals. Males obtain all their energy from sweet fluids such as nectar and honeydew. Since they don't lay eggs, male mosquitoes do not require a protein source and do not bite.

Close-up of female mosquito The elongated proboscis of this female mosquito enables it to obtain the protein it requires for egg development and maturation.
Image: sondebueu
Source: sondebueu via cc
 

Adult females lay eggs in or near water, commonly on vegetation, a few days after a blood meal. The life cycle includes four larval stages, or instars. Between each instar the larva moults in order to grow. The larvae, or 'wrigglers' (so-called due to their characteristic movement), typically inhabit stagnant water bodies, and must come to the surface periodically to breathe through spiracles or a siphon. The larvae of some species use their mouth bristles to filter water for microorganisms, while others scrape food particles off the surfaces of submerged objects. The pupa does not feed but must come to the surface to breathe through respiratory trumpets.

mosquito larva The mouth bristles, used in filter feeding, are clearly visible on this wriggler. Note also the three body segments and the segmented abdomen.
Image: Tim Blackburn
Source: Museum Victoria
 

Female mosquitoes inject saliva that contains an anticoagulant into their host to prevent blood-clotting. The saliva also contains components that cause vasodilation (to increase blood blow) and suppress the immune response of the host (to protect the mosquito). Once the feeding episode ends, the host produces antibodies which trigger a release of histamine. This in turn increases the permeability of adjacent blood vessels, thereby enabling a stronger immune response. The blood vessels swell and this causes the familiar, itchy lump—the 'mozzie bite'.

Female mosquito A female mosquito just after landing on my toe as it commences a blood meal. Note the thin abdomen at the start of the meal.
Image: Tim Blackburn
Source: Museum Victoria
 

Female mosquito feeding The same mosquito one minute later. Note the swollen abdomen which is red because it is full of my blood.
Image: Tim Blackburn
Source: Museum Victoria
 

Viruses and pathogens are easily transferred between mosquito and host via the saliva. Mosquitoes are serious agents in the transmission of diseases such as dengue and yellow fever, malaria and lymphatic filariasis. In 1996, the World Health Organisation estimated that several million people die each year from mosquito-borne diseases around the world. Each disease is spread by a specific type of mosquito; malaria is spread by Anopheles spp. and dengue fever is primarily spread by Aedes aegypti.

However, mosquito-borne diseases are rare in Victoria, and mosquitoes here are more likely to annoy rather than cause disease. You can prevent bites by wearing insect repellent and protective clothing, and removing breeding sites. Window mesh and mosquito nets also help exclude potentially harmful species, particularly in tropical and subtropical areas. Various plant species such as Citronella Grass, Rosemary, Catnip and Marigolds repel mosquitoes and may be especially useful if planted near doorways and windows. 

Links:

CDC: Mosquito-borne diseases

Vector-borne diseases in Victoria

Bug of the Month - Emperor Gum Moth

Author
by Patrick
Publish date
4 January 2013
Comments
Comments (9)

The apparent decline of the Emperor Gum Moth (EGM), Opodiphthera eucalypti, around Victoria has been a hot topic of debate amongst entomologists and other EGM fans in the last few years.

Emperor Gum Moth A newly-emerged male Emperor Gum Moth.
Image: Patrick Honan
Source: Patrick Honan
 

The decline is anecdotal and as yet there is no hard evidence, but theories abound. Many people contact us noting that they don’t see EGM caterpillars anymore, as they did when climbing trees as a kid. Which prompts a question in return: "When did you last climb a tree?"

Emperor Gum Moth Male Emperor Gum Moths have enormous feathery antennae used to detect the presence of females.
Image: Patrick Honan
Source: Museum Victoria
 

Another possibility is the demise of the introduced Peppercorn Tree (Schinus molle) in Victoria. Originally from the Peruvian Andes, Peppercorns were planted in every Victorian primary school and many parks from the 1880s to the early 1900s. EGM caterpillars, although feeding naturally on eucalypts, will also consume Silver Birch (Betula pendula) and Liquidambar (Liquidambar styraciflua), as well as Peppercorns. Victorians who went to primary school up until the 1970s would be very familiar with EGM caterpillars feeding on Peppercorns, but the trees have gradually died out or been removed until now there are very few left. Peppercorns are now considered an environmental weed.

Children planting trees State school children planting peppercorn trees in Carlton Gardens, just outside the now Melbourne Museum, on Arbor day, 1905.
Source: Reproduced from Carlton in DPCD report by Lovell Chen
 

Emperor Gum Moth The colour of adult Emperor Gum Moths varies considerably throughout their range.
Image: Patrick Honan
Source: Patrick Honan
 

Another strong possibility is the intrinsic variation in insect populations. Many species undergo booms and busts, appearing in vast numbers one year then apparently disappearing for several years afterwards, sometimes for a decade or more. These fluctuations are usually climate related, with each species requiring an exact combination of factors (such as a mild winter and a wet summer) in a particular order to afford them a boom year. Perhaps the last couple of decades have not produced the right combination for EGMs, and they’re just waiting for their number to come up.

European Wasp The dreaded European Wasp. Workers tear EGM caterpillars off trees and cut them into small pieces before transporting them back to the nest.
Image: Patrick Honan
Source: Patrick Honan
 

One of the most popular theories is attack by European Wasps (Vespula germanica) on EGM caterpillars. Caterpillars are a favoured prey of European Wasps, and they can do enormous damage when present in large numbers. However, somewhat ironically, after reaching plague proportions in the 1980s and 90s, wasp populations have dropped dramatically in the last 15 years or so, again for no discernible reason other than a possible combination of environmental factors.

Emperor Gum Moth caterpillar feeding An Emperor Gum Moth caterpillar feeding on Eucalyptus species.
Image: Patrick Honan
Source: Patrick Honan
 

In the end, any decline of EGMs probably comes down to habitat loss. The number of host gum trees has steadily reduced in urban areas in particular, but also in suburban areas and even rural towns. If fewer trees are available, there will naturally be fewer caterpillars. So if you’re missing these iconic caterpillars, the best strategy is to plant a gum tree.

Young caterpillars Young EGM caterpillars look very different to older caterpillars, but their presence is a possible sign of a healthy local environment.
Image: Patrick Honan
Source: Patrick Honan
 

But these theories are, at this stage, pure speculation. EGMs are still around, if you know where to look. A Museum Victoria Bioscan at Wilson’s Promontory in 2011 attracted hundreds of EGM adults (as well as the closely related Helena Gum Moth, Opodiphthera helena) to light traps at night. And just last month, a dozen EGM caterpillars were on display in the Forest Gallery at Melbourne Museum. Plans are underway to assess the extent of the EGM decline in Victoria, so stay tuned for further developments.

Further reading:

Coupar, P. & Coupar, M., 1992, Flying Colours – Common Caterpillars, Butterflies and Moths of South-Eastern Australia, NSW University Press, 119pp.

Common, I.F.B., 1990, Moths of Australia, Melbourne University Press, 535pp.

Zborowski, P. & Edwards, T., 2007, A Guide to Australian Moths, CSIRO Publishing, 214pp.

Bug of the Month - Giant Grasshopper

Author
by Patrick
Publish date
3 December 2012
Comments
Comments (2)

The Giant Grasshopper is so named for being the largest grasshopper in Australia. The adult's body length, however, varies from an enormous 90mm to less than half that size. This gives it the scientific name Valanga irregularis, referring not only to the irregular colouration but also the irregular length. People who know the species well simply call it Valanga.

grey grasshopper The mottled grey form of the Giant Grasshopper, common around Townsville, North Queensland.
Image: Patrick Honan
Source: Museum Victoria
 

Unlike many of the better-known grasshoppers, this species feeds not on grass but on the leaves of shrubs and trees. They have a very variable diet, ranging from native plants to citrus, cotton, coconut and even coffee plants. This makes them a minor pest in some areas, due to their occasional habit of consuming every leaf on a food plant when present in large numbers.

brown grasshpper The spectacular brown version of the Giant Grasshopper common around Iron Range, North Queensland.
Image: Patrick Honan
Source: Museum Victoria
 

Giant Grasshopper nymphs change colour with each moult, varying from light green to a spectacular red with blue stripes. The eggs are laid in batches of up to 150 within 'pods', made of a frothy substance that hardens upon drying. The eggs are sometimes attacked by a tiny parasitic wasp (Scelio flavicornis), which lays its own eggs inside the grasshopper's eggs, the wasp grubs feeding on the embryo within.

Brown and green forms of immature Giant Grasshopper Left: A young nymph. Right: An older bright green nymph.
Image: Patrick Honan
Source: Museum Victoria
 

Adult grasshoppers are very sensitive to movement and will leap away at the slightest disturbance. They can fly upwards as high as two metres, then horizontally in a straight line until they hit the ground. However, Giant Grasshoppers tire easily and the length decreases rapidly with each consecutive leap.

face of Giant Grasshopper A close encounter with a Giant Grasshopper from the Northern Territory.
Image: Patrick Honan
Source: Museum Victoria
 

Giant Grasshoppers occur across the top of Australia and there are a number of closely related species, at least four of which are undescribed. They are all very difficult to distinguish from each other, due to variations in most of the important characteristics, including size.

Giant Grasshopper eating A captive adult Giant Grasshopper satisfies its ravenous appetite with Orthopteran mix.
Image: Patrick Honan
Source: Museum Victoria
 

This species survives very well in captivity, feeding on a combination of fish flakes, grass seed, muesli, and pollen (known as Orthopteran mix). Unlike other insect species, they show no signs of inbreeding – a single mated female may be sole progenitor to tens of thousands of descendants over many generations without a single sign of genetic deformities.

exhibition display cases The Habitats exhibit, home of the Giant Grasshopper and many other spectacular creatures in Bugs Alive!
Source: Museum Victoria
 

Giant Grasshoppers can be seen in the Habitats exhibit in Bugs Alive! at Melbourne Museum.

Bug of the month - Steel Blue Sawfly

Author
by Patrick
Publish date
1 July 2012
Comments
Comments (12)

If you're out in the bush or a local park during winter, you're likely to happen across a group of 'spitfires' clinging to the branch of a gum tree in the cold. These insects are technically called sawflies, a group of insects closely related to wasps. There are more than 200 species of sawfly in Australia, but the local species is the Steel Blue Sawfly (Perga dorsalis).

sawfly larvae A small clutch of sawfly larvae clinging to a branch.
Image: Patrick Honan
Source: Museum Victoria
 

The name 'sawfly' derives from a 'sawbench' under the abdomen of the female with which she lays eggs. Female wasps, in contrast, use a pointed ovipositor to lay eggs and in some species this doubles as a sting – adult sawflies do not sting and both adults and larvae are completely harmless.

Patrick Honan Female Steel Blue Sawfly.
Image: Female Steel Blue Sawfly
Source: Museum Victoria
 

Female sawflies use the sawbench to cut the upper surface of a leaf and deposit 60-70 eggs into the leaf tissue. The larvae hatch and feed on gum leaves, grouping together for protection in a rosette pattern, similar to the head-outwards stance adopted by Bison when under attack. This is known as a 'ring defence', or cycloalexy. As the larvae grow, they collect in larger groups around branches during the day and spread out to feed at night.

sawfly eggs A raft of eggs cut into a gum leaf by a female Steel Blue Sawfly.
Image: Patrick Honan
Source: Museum Victoria
 

Like their cousins, the ants, bees and wasps, sawflies show some social behaviour but only in a primitive way. When feeding at night, larvae tap the branch to keep in constant communication with each other. If an individual becomes lost, it will tap more rapidly until it receives an answer from the rest of the group – if an individual becomes completely separated it will not survive long on its own.

Detail of sawfly larva abdomen. Sawflies grouped together on a branch. The pale tips of the abdomen are tapped on the branch to keep in touch.
Image: Patrick Honan
Source: Museum Victoria
 

The activities of a group of sawfly larvae are governed by a few select individuals that become in effect the leaders of the group. They lead the rest out to feed at night and, if they run out of food, lead the group across the ground to other trees. When large numbers of sawfly larvae are present they are able to defoliate small gum trees, but in general are not a major pest.

mass of sawfly larvae A mass of sawflies resting during the day, the result of the merging of several smaller groups.
Image: Patrick Honan
Source: Museum Victoria
 

When ready to pupate, the larvae leave the host tree and burrow down to make mass cocoons in the soil. Here they sit through spring and summer to emerge in early autumn. Adults have no mouthparts and do not feed, living only for a week or so.

pupating sawfly larvae Sawfly larvae in their pupal cells underground, preparing to pupate.
Image: Patrick Honan
Source: Museum Victoria
 

Not all emerge, however, as many succumb to parasitic flies. These flies, about the size of a blowfly, will lay eggs in the sawfly larvae and the fly maggot literally eats its host from the inside out, eventually emerging from the sawfly's cocoon.

parasitised sawfly larva An opened pupal cell showing the consumed sawfly larva on the left, and the engorged parasitic fly larva on the right.
Image: Patrick Honan
Source: Museum Victoria
 

Sawfly larvae have an unusual defensive mechanism that has given them the name 'spitfires'. They store eucalyptus oil in a small sac in their gut, and regurgitate this oil when under threat. Despite their nickname, they are unable to actually spit this fluid and the oil itself is harmless unless eaten (like all eucalyptus oil). In fact it has a very pleasant eucalytpusy smell.

sawfly larva mouthparts A large blob of frothy regurgitate in the mouthparts of a sawfly larva.
Image: Patrick Honan
Source: Museum Victoria
 

Australia is one of the main strongholds of Symphyta, the suborder of insects to which sawflies belong. The Steel Blue Sawfly is one of the few insect species active in Victoria during winter, so next time you're in the bush take the time to stop and smell the sawflies.

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