Christmas Bells

Christmas Bells
Christmas Bells - Blandfordia nobilis

Saturday, February 15, 2014

Sawfly guarding eggs on Rubus nebulosus

Bob McInnes, of REPS, brought me an interesting insect this morning. It is a female Sawfly Philomastix macleaii (apparently renamed Philomastix glabra) which was guarding a set of eggs she had laid on the underneath side of the leaf of the Green-leaved Bramble, Rubus nebulosus, a very sharply thorned Bramble with pinnate (5-foliolate) leaves. The specimen of leaves (and associated insect and eggs) came from Tony and Anna Williams's (not "Windsor" - apology for previous typo) property in Robertson. 

They have a very fine patch of "Cool Temperate Rainforest" on their hill. It differs somewhat from the rainforest in the Robertson Nature Reserve, as it is largely dominated by Lilly Pilly Syzygium smithii and Blackwood Wattle Acacia melanoxylon but their patch of Rainforest has some other uncommon trees, such as the Acronychia oblongifolia and the Black Olive berry (Elaeocarpus holopetalus) and their forest also has many large Birds Nest Ferns. (No doubt there are other differences which I have overlooked.)

The Sawfly is well reported to "guard" its eggs and larvae.
In the case of a closely related species, the guarding behaviour is described as follows.
"Females place their eggs in groups of 30-40 on the leaf underside on both sides of the midvein and later position themselves at the base of the leaf where the larvae feed on, with the head directed towards the stem."

Source: Pergidae of the WorldAn online catalogue of the sawfly family Pergidae (Symphyta)

That description matches exactly what this insect was doing - guarding her eggs.

Green-leaved Bramble, Rubus nebulosus
Philomastix macleaii female guarding eggs
Note how she is positioned at the 'base" (stem end) of the leaf.
This is to protect the eggs (and subsequently the larvae)
from crawling insects, such as ants.

Note similarities of this image with another image
guarding her eggs laid underside of
a Rubus moluccanus.
Similar posture, similar food plant.
Similar appearance, including long yellow antennae.
Philomastix macleaii 
female Bramble Sawfly

Eggs of the sawfly. Philomastix macleaii
Unlike eggs in earlier linked image, these are dark.
presumably well advanced towards hatching,
Check this image of similar purple eggs
of a Raspberry Sawfly.
Females of Philomastix spp. pierce the leaf from above and place the egg on the underside of the leaf (Macdonald & Ohmart 1993). All species of this genus exhibit maternal care. Females stand near their egg mass and young larvae or near the leaf petiole with the head directed to the stem and when disturbed they shake and create a buzzing sound with their wings (Macdonald & Ohmart 1993, Naumann & Groth 1998). This behaviour lasts until they die.

Click on image to enlarge.
There are tiny cuts in the upper surface of the leaf
presumably each cut relates to where the egg is underneath.
Does she protrude her "ovipositor" through the leaf?
That's the only thing which makes ergonomic sense
otherwise it would require the female to go to both sides of the leaf
and match up the cut with the egg.
Ockhams Razor would rule that out.

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