Our Bushland Diary

Wednesday, August 31, 2011

Pepper and salt, mistletoes and insect interactions

We're heading into the time of year in which the bushland lights up with a thousand shades of yellow, orange, pink, gold and purple, and I simply can't go for a bushwalk without my camera.  There are so many different flowers to delight the photographer; orchids, hibbertias, leschenaultia, hakeas, native peas, acacias, cottonheads and kangaroo paws, to name a few*.  

One plant I particularly like (among these hundreds of species) is known colloquially as "Pepper and Salt".  The scientific name for it is Philotheca spicata.  It isn't the most spectacular flower in the bush, not by a long shot, but it makes up for being somewhat photogenically challenged by having a pleasant and elusive perfume, and always seems to have a posse of insects flittering around the delicate flowers.

Flowers of "Pepper and Salt" (Philotheca spicata)

The plant itself grows as an upright shrub, usually no taller than 50cm, with a slightly weeping habit especially when in flower.  (The gracile branches seem to be weighed down by the flowers.)  It is fairly widespread in our local bushland such as the Bush Forever sites, in banksia woodland, or amongst jarrah and marri trees.

"Pepper and Salt" (Philotheca spicata)
Pepper and Salt is found along much of the Swan Coastal Plain and further south (at least where it hasn't been cleared for roads and buildings.)  It would make a fine addition to a bush garden, but in nurseries you might have to search for it, or order it, under the old botanical name of Eriostemon spicatus.

Satin-green Forester moth (Pollanisus viridipulverulenta)
The little moth in attendance could be mistaken for a butterfly - it moves around in broad daylight, its iridescent green, blue and copper wings glittering in patches of sunlight.  Due to its romance with the Philotheca flowers, and its general reluctance to move from a good position, I find this species not too difficult to photograph.  

Satin-green Forester Moth
According to my field guides, this species is the Satin-green Forester Moth (Pollanisus viridipulverulenta).  Entomologists, please correct me if I'm wrong! The wikipedia entry doesn't mention that it is found in WA, but the CSIRO website shows that it is. 

Insects such as butterflies and moths are usually reliant on specific plants for food and drink.  Some of these little animals are entirely dependent on just one or two species.  Some have had deserved scientific attention.  For example, caterpillars of the Satin Azure butterfly (Ogyris amaryllis) dine on mistletoe (Amyema species).  Unfortunately, many people remove mistletoes, believing that their parasitic qualities will weaken and kill their trees.  See this ABC website for a great expose on the myths and facts of mistletoe.

Here is a fact sheet you can download about the Satin Azure, written for South Australia.  Interestingly, although the Satin Azure is found across Australia, in each area it feeds on the local Amyema species available.  In the factsheet, it mentions Wireleaf Mistletoe (Amyema preissii) as a favourite food plant, and Stalked Mistletoe (A. miquelii) as a back-up; these are two mistletoe species we have around Perth.  The butterfly also needs "attendant" ants to complete its life-cycle.

Wireleaf Mistletoe (Amyema preissii) grows on Acacia trees
Can you see the ecological links here?  In this case, the butterfly lays its eggs on a plant that is totally reliant on another plant (i.e. wattle trees).  The caterpillars of the butterfly are protected from predators by the attendant ants .  Do the mistletoes benefit from this arrangement?  And what do we know about the ants' requirements?  What do they feed on?  Does the wattle provide an ideal habitat in the way of leaf litter?  What are the requirements of the wasps that might parasitise the caterpillars?  We know a little, but not very much really.  (At least there are a few articles of interesting research listed on the internet about this!)

These fauna-flora interactions are not widely studied, and have not been fully considered in our planning for conservation reserves, rehabilitation of industrial areas, and revegetation of urban landscapes.  Part of the problem in the past has been that people have studied plants (i.e. botany) or insects (i.e. entomology) and not the link between the two sciences (i.e. ecology).  In fact, botanists have tended to look askance at insects as a threat - something with the potential to destroy the perfect plant specimen, or wreck a photo of an ideal flower (where some little critter has chewed one of the petals, for example.) 

Horticulturists have moved one step further from nature, with their arsenal of poisons to deal with their unwanted fauna in the form of bug sprays.  It saddens me to think how many caterpillars might be being sprayed today in my suburb, because they are not recognised as being butterfly larvae.  Ecological links are broken.  No caterpillars; no birds to feed on them = Silent Spring.  (Yes, it's a book; read about it here.)

Entomologists have in the past sometimes lacked the botanical skills to record the plants on which their study animals have depended.  At the present, following little animals around in bushland still requires patience, time and a lot of skill, so it does not fare well in the cut-throat budgets and high-pressure timelines of a typical land "development" or mining project.  Why on earth would a high-flying developer think they need an entomologist?  Add in the "emotional care factor" (i.e. cute fluffy animals versus scaly ones or buzzy flitty ones) and it's difficult to get people to realise their importance.  Maybe in another fifty years we'll have a better idea of ecological links.  So our Bush Forever sites and little urban parks may be more precious than we yet realise, especially at their current rate of disappearance.

There is a lot more to be learnt about our local bushland. . . 

* Note to the people who maintain our local Public Open Spaces - August is NOT the time to prune these plants!  You will be removing the recent winter's growth and flower buds, and depriving us of our coming show of spring flowers.  Please wait until late summer or autumn next year before getting out your pruning equipment.

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