Helen Schwencke postedRather than filling the 26/6/22 invitation thread, here goes:
Andrew replied to my offer for members to visit my West End butterfly and wildlife garden for a tour and discussion about encouraging increased biodiversity by growing local native plants along with our food plants, with
“I think that would be wonderful Helen. I'm over-run with ants farming scale on everything here so I'll get in quickly and say, "Pick me!" I'm very interested in what I can grow to that will help attract good predators.
At my garden tour/visit, the discussion I’m hoping to have would be about looking for approaches to reduce competition for the food we grow, based on the highly specific relationships different local native plants, insects, predators and parasitoids, have with each other, and how this can help us. The concept is that the larger the variety of local native plants we can grow, the more able our gardens will be to help regulate themselves, though this is always in a state of ebb and flow and change, and influenced by a variety of other things.
In my own case, several years ago, I was overrun by small black ants. I had 6 lane superhighways of the ants climbing up several house posts of my workers cottage and nesting in all sorts of places inside. A sub-colony even took up residence in the spines of my two-volume hardcover “Butterflies of Australia”, along with various electrical equipment. The twist was that the book’s contents discussed various species of ants that attend and support butterfly caterpillars, as I had seen this ant do for some (Lycaenid) butterfly caterpillars in my garden. I’d been leaving the ants alone, welcoming the small extra survival advantage that they bestowed on these caterpillars.
At a certain point, the situation became just too much, even for me, to take. I had noticed that a particular north Queensland plant, lolly vine, Salacia chinensis, with purportedly yummy fruit, had become rampant in my back garden, and was covered in sooty mould. This was being spread to many other plants in my rather densely packed mini-jungle (or pocket forest). A closer inspection showed me that small black ants, an introduced Tramp ant species, identified by the Qld Museum as a species of Technomyrmex, was responsible both for spreading the sooty mould and for occupying way too many useful objects in my house.
I’d had the lolly vine growing for some 20 years, both for its fruit and to support the caterpillars of butterfly species. I had hoped that the north Qld butterfly would find it eventually, even though it was well out of its range, and also a local butterfly, the White-banded Plane. This had not happened. The lolly vine had some, less than useful or pleasant, features such as that it wasn’t fruiting (so no food), and when it was in flower I kept smelling what I thought was sewage (so perhaps the fly pollinator that the smell was designed to attract was absent, leading to no fruit), also when canes died back they became hard and sharp and difficult to remove, so I decided its presence was no longer appropriate for a small 16 perch (405sq m) block and chopped it all back. This action removed the bulk of the ant / sooty mould, and my ant superhighways, problems very quickly. Clearly, the conditions weren’t appropriate to be growing that plant, either for food or as a butterfly host plant. Also, I’ve since grown quite suspicious of plants that grow too well and aren’t obviously feeding any small creatures.
A solution for Andrew’s situation, and possibly for others with a similar problem, may be to do some detailed observations, identifying the species involved, and trying to see what the relationships are between the various garden components. However, the situation may well need some "picking apart" to understand what's actually going on.
By far and away most host plant-insect relationships are highly specialised, with the host plant only supporting a limited number of herbivorous insects, and the insects only using a small number of local native plants. Introduced species of plants or those out of their natural range are highly likely to have few associated insect herbivores. On the other hand, introduced insects that do become established are highly likely to be able to use a broader range of native and exotic plants – and then, of course, there are the exceptions. Each of the problems in our gardens may have a different solution, depending on which species are involved. There’s no “one size fits all” when it comes to nature-based systems.
For starters, there are some 256 ant species that have been identified as living in the Brisbane area, according to surveys by the Qld Museum that were reported in the BCC's report "Terrestrial Invertebrate Status Review of Terrestrial" (2005). Unfortunately, that study didn't include any surveys of scale insects. The picking apart may need to involve finding out which species of ants farm scale and if any are host-specific to the plants being grown, and which species of ant-farmed scale have a specific relationship with which scale-farming ants and are these scale specialised to specific host plants.
Having only scratched the surface with this post helps me to remember how much I love the exquisite and amazing complexity of Life on Earth. I also love sharing this. My most recent book, where I explore some of this topic is called “Inviting Nature to Dinner”.