We are currently researching the pollination requirements/restrictions/deficiencies and other potential threats impacting on an endangered plant species, Astrotricha roddii, Rodd’s Star Hair (Fig. 1), a species that has been in decline for many years in response to droughts and over-grazing by goats. This project is a collaboration between researchers at the University of New England (Australia) and the NSW Department of Planning Infrastructure and Environment.

Figure 1. Astrotricha roddii in its natural habitat, in sclerophyllous woodland on granite in north-western New South Wales.

In November 2020 we visited the only known, vigorous population (fenced off from goats) that was in flower to begin our investigation of the plant’s pollination ecology.
We saw three species of bees at the Astrotricha roddii flowers. The most common species was a Lipotriches species, possibly L. phanerura; one was a Megachilid species (Fig. 2), yet unidentified; and the third was a small black bee!, probably a Halictid but I saw only one and very briefly – it was eating the pollen into a crop like some Halictids do, so unlikely to be a good pollinator. Oh, there were also some honeybees competing with the native bees at the flowers 😦

I have never seen so many Lipotriches together at the same time! It was amazing! This certainly supports our idea that these bees can survive in stasis underground – as pupae probably – for extended periods (multiple years) to survive through drought periods. We didn’t see these bees before or after the Astrotrichas were in flower. Interestingly, there were some Haemodorum plants just coming into flower – which we know are pollinated by Lipotiches spp. – and there were also Dianella and Hibbertia species in flower, co-occurring with the Astrotrichas – these two plant genera don’t produce nectar, just pollen, so are dependent on co-occurring nectar-producing flowering species (such as the Astrotichas :)) to supply pollinators with nectar/energy. The pollinators of Dianellas and Hibbertias need to be bees such as Lipotriches species that are capable of buzz-pollinating plants like these that have poricidal anthers … which is all rather neat 🙂 and very exciting for pollination-ecology nerds.

Figure 2. A megachilid bee on Astrotricha roddii, with a great load of pollen.

We saw honeybees robbing nectar from Grevillea masonii recently.

The actual pollinators we observed were all birds – several species of honeyeater. They didn’t appear to be disturbed by the honeybees feeding in the same shrub. It’s possible though ( as shown in other studies) that the birds had to forage over more plants to get enough food resources owing to the nectar depletion by the honeybees. Perhaps the honeybees actually encouraged more outcrossing as a result – Our breeding system work showed the grevillea to be an obligate outcrossing species so the honeybees could be having an indirect positive effect on seed set….. food for thought and another study.

It seems to be a common problem (if it is a problem) for grevilleas – we’ve seen honeybees stealing nectar from other species such as G. beadleana, another threatened species, seen here (below) in Guy Fawkes River National Park recently:

Judging by the lack of any pollen remaining on the pollen presenters it appears the real pollinators of this grevillea – shown to be Eastern Spinebill honeyeaters in a study by Caroline L. Gross – are doing a fine job of pollination, and we saw plenty of fruit being set (below) …..

… and plenty of seedlings germinating under dead adult plants after recent fire:

We have been getting into our sites to assess recovery after the 2019-20 fires (this has often required the 4WD winch and a chainsaw to clear the way in). Superficially, plants appear to be recovering, as in the following image of the main track into Gibratar Range National Park.

This is hardly surprising – the Australian vegetation has been adapting to fire over millions of years. What it may be having problems adapting to, though, is increasing fire frequency. In Gibraltar Range National Park there are areas that haven’t been burnt for over 50 years but this last fire season saw that change.

 

Some of these long-unburnt areas adjoin patches of rainforest that have been protected by these buffer zones but even rainforests suffered in the recent fires. They also suffered in the preceding drought with many species within rainforest patches hit particularly hard, such as these walking stick palms, below.

A closer look shows some plants recovering by resprouting, like the eucalypts, and others recovering through seedling germination, like the Gibraltar Range Waratah seedlings below.

Other species show no signs of recovery yet, like Conospermum burgessiorum. We found this single adult (below) but no resprouts and no seedlings where we know there were many plants before the fire. Perhaps it is a species that will germinate in spring?

What I will be particularly interested to see is how the pollinators recover!

Recently we acquired a new garden addition that came with an unexpected bonus. We bought a Gardenia; but didn’t notice it had at least one passenger – a moth caterpillar! We found out when we saw the adult visiting our Buddlejas 🙂

Cephanodes spp moths are a group of hawkmoths in which the larvae feed on various members of the Rubiaceae family, including Gardenias. The larvae pupate in the soil – maybe that’s how it snuck through! What a beautiful creature to see in our own back yard 🙂

We just published a paper showing pollinators experienced higher levels of reproductive success in isolated trees at a fig species’ expanding range margin, in spite of there being lower numbers of pollinators in these isolated trees (half as many) as there were in larger populations of fig trees. This increase in reproductive success was partly a consequence of parasitoid release (Mackay KD, Gross CL, Ryder DS., Increased reproductive success through parasitoid release at a range margin: Implications for range shifts induced by climate change. J Biogeogr. 2020;00:1–15. https://doi.org/10.1111/jbi.13795).

The ‘insect apocalypse’ is a theme that has been taken up as a popular discussion point lately, driven in part by recent papers such as ‘Worldwide decline of the entomofauna: A review of its drivers’ by Sánchez-Bayo and Wyckhuys. Those of us who work in this area – entomologists, insect ecologists and others – have been aware of declines in insect abundance and diversity for decades. Unfortunately, because our understanding of these declines is limited there are multiple views, and multiple claims and counter-claims made concerning the geographic and taxonomic extents of these declines; and the discussion has become somewhat emotional at times…like all worthwhile discussions! What I think we can all agree on is that old chestnut: ‘more work needs to be done’. In the meantime, as more work is done and our understanding improves, let’s welcome all the sources of information available and all the different points of view and let’s keep the discussion going!

A preprint of a very interesting paper was published this month on the subject of bee decline: Eduardo E. Zattara and Marcelo A. Aizen, Global Bee Decline. Dec. 10, 2019; doi: http://dx.doi.org/10.1101/869784. They found the numbers of collected bee species recorded in global occurrence records sourced from the Global Biodiversity Information Facility have decline today to half of those recorded in the 1950s.

The image above is of Exoneura bicolor on a flower of Leptospermum novae-angliae, the New England Tea-tree. This tea tree (a shrub) is a ‘co-factor’ in the pollination ecology of a threatened species on native mint, Prostanthera staurophylla – known as a co-factor because it provides nectar to pollinators on which P. staurophylla depends and is therefore an important component of P. staurophylla‘s plant-pollinator network. There are only about 100 plants of P. staurophylla left in the wild. We are currently working out the species’ pollination needs and also working closely with the Department of Planning, Industry and Environment on a translocation experiment to establish some back-up populations of this endangered plant.