The Cherry Tree & The Meat Ant


This is a video about ants which visit my cherry tree. The story is primarily about meat ants (Iridomyrmex purpureus), but a couple of other species make cameo appearances. Why do the ants climb into my cherry tree? You’ll have to watch the video to find out!

I hope you enjoy the video – as usual, being ‘one minute bugs’, it’s short and sweet! Let me know what you think. Please hit the subscribe button in the widget if you would like to receive email alerts about new posts. The subscription process is more than one click, but it won’t take too long!

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Gall-inducing insects

I was doing a bit of Spring cleaning on my blog and noticed that this post is the most popular post I have ever written. Usually I am lucky if I have 500 people read one of my posts, but this one has clocked up a whopping 8738 hits! So I am republishing the post for those that missed it when I first published it in October 2015.

Have you noticed strange lumps and bumps on the leaves and stems of some of your Australian native plants? Galls are especially common on gum trees and wattles, and they are abnormal plant growths that form in response to invasion of plant tissue by a variety of organisms. Galls can be caused by certain species of wasps, flies, beetles, psyllids, coccids, thrips, moths and aphids, as well as by nematodes, mites, bacteria or fungi.

Galls form as a reaction to insects feeding on, or their eggs being laid in, plant tissue. When a female gall-inducing insect deposits her egg in the leaf or stem of a host plant, a biochemical reaction between the egg and the host may produce the gall, inside of which a hatching larva will feed. Or the larva may modify the plant’s normal response to injury with salivary secretions, which stimulates the plant to grow the gall (rather than scar tissue), resulting in food and shelter for itself. Gall-inducing insects (adults and juveniles) are usually very small, rarely more than a few millimeters in length, but the galls they induce are much more obvious.

citrus gall waspGall wasps are found throughout the world, and the most well-known gall wasp in Australia is the citrus gall wasp (Bruchophagus fellis) which forms grotesque stem galls on all varieties of citrus (above). Citrus gall wasp is actually an Australian native insect whose native host is the Australian finger lime (Citrus australasica). It has grown to love our cultivated lemons though!

Galls formed by other species of wasps are found on eucalypts, acacias, banksias and some cut flower natives like Geraldton wax and Thryptomene.

Wattle apple gallGalls on wattles are often called “apple” galls (above) and are induced by wasps of the genus Trichilogaster. Depending on the species of wasp and the size of the gall, hundreds of larvae may feed inside a gall. Some species of wasps form galls on leaves which are characteristically spherical and are bisected by the leaf margin, and often cause leaves to twist. Galls formed by other insects are located on only one side of a leaf.

gall midgeFlies which form galls are usually midges in the family Cecidomyiidae. The larvae of some gall midges cause a thickening and shortening of leaflets, or pimple-like blisters (as above) on leaves (especially on eucalypts). Eucalyptus leaf galls usually contain a single orange or red larva which distinguishes it from most other larvae found in galls which are typically cream or white in colour.

apiomorpha gallCoccids are related to scale insects and cause hard woody galls, some of which have distinctive shapes. Galls caused by male coccids are usually a different size and shape to those caused by female coccids. The gall-former shown (above) is a species of Apiomorpha in the family Eriococcidae. Female Apiomorpha induce the large stem galls, while  males induce the small leaf galls that you can see.

psyllid gallPsyllids in the family Triozidae cause galls on native trees. Schedotrioza spp. form distinctive spherical “apple” galls on eucalypt leaves (above). The galls of the notorious lilly pilly psyllid (Trioza eugeniae) are quite different (below). The nymphs of this pest form pit galls on flush growth usually on the underside of a leaf with a corresponding lump on the upper surface. Unlike most other gall insects the nymphs are not fully enclosed by the gall. The nymphs are the small flattened yellowish creatures in the image below.

lilly pilly psyllidSome varieties of lilly pilly like Syzygium luehmannii and Acmena smithii are less susceptible to attack than others. But lilly pilly shrubs of susceptible species (such as Syzygium panicultaum and Waterhousea floribunda) can be devastated by psyllid attack. Most other gall-inducing insects are not so serious though, an infestation won’t kill a tree or shrub, but can be unsightly and may affect plant vigour.

Identification of gall-forming insects is not easy. You could keep a gall in a jar to see what emerges, but that may not help because what emerges might be a parasite of the insect which caused the gall, or a hyperparasite (parasite of a parasite). Sometimes an egg may be laid into a gall already containing the larva of a different species, the new egg hatches and the emerging larva will feed in the gall alongside the original larva. When they both hatch out as adults you won’t know which insect caused the gall. Insects which adopt this ‘cuckoo’ style of living are known as inquilines. Insects never cease to amaze me!

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Sheep in Wolf’s Clothing

Insects that are armed with powerful stings are often strikingly coloured to warn off potential predators – a strategy known as aposematism . A good example of this is the black and yellow colour pattern of the European wasp (Vespula germanica).

Vespula germanica

Some harmless insects take on the appearance of aposematic insects even though they are not actually dangerous themselves. Hover flies are an example of this. One common hover fly species the drone fly Eristalis tenax – is an excellent bee mimic, and was the star in a recent ‘one minute bugs’ video (link).

Other common hover flies (image below) are harmless flower visitors but their striking yellow and black markings superficially resemble the markings of bees or wasps. Bees and wasps usually have stings and consequently are left alone by many predators. Hover flies don’t have stings, so by adopting colour patterns similar to bees and wasps this affords the hover flies some protection. This defence strategy is known as Batesian mimicry.

Bee mimic

Now for a wee bit of history. H.W. Bates (hence ‘Batesian’) was the first scientist to conduct a major study on mimicry – in the Amazon Basin in the 1860s. Charles Darwin recognised Bates’s work on mimicry as critically important to the theory of evolution, and cited it extensively in later editions of his own great work The Origin of Species. Darwin appears to be quite a fan, because in a letter to Bates in 1862 Darwin wrote:

“Dear Bates. I have just finished, after several reads, your paper. In my opinion it is one of the most remarkable and admirable papers I have ever read in my life.  .  . Your paper is too good to be largely appreciated by the mob of naturalists without souls; but, rely on it, that it will have lasting value, and I cordially congratulate you on your first great work.”

I am particularly intrigued by insects which mimic other insects that would normally appear very different from their own body shape. It’s easy to see how a yellow and black patterned fly could look like a bee or a wasp (e.g. the hover fly), but how about a beetle which looks like a spider-hunting wasp? The yellow-horned clerid beetle Trogodendron fasciculatus (Cleridae) – image below – mimics the spider-hunting wasp Fabriogenia sp. (Pompilidae) – lower image.

Trogodendron

If you place them side-by-side you might think the resemblance is only superficial – dark bodies and yellow/orange antennae. It’s when they move that you see mimicry at its best. Spider-hunting wasps move in a characteristically jerking manner and flick their antennae constantly as they look for spiders. The yellow-horned clerid beetle mimics these movements exactly, so much so that when you see one moving you would swear that it is a wasp. The beetle would then be completely safe from predators especially spiders. No sane spider would want to go near an insect that appears to be a spider-hunting wasp!

Spider wasp
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