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biocontrol, ecology, insects, invasive species, nature, pest management, thistle, tortoise beetle, weevil
There are many, many non-native trouble-making species in this world.  They come in all shapes and sizes, but they share in common several features. They are introduced (accidentally or deliberately) by humans, spread like wildfire, cause economic and/or environmental damage, and require money to manage. A species that fills the above criteria is considered to be a non-native invasive species.
Among the brute force methods (i.e. burning, cutting, hunting, trapping, removing vegetation, applying pesticides), we have also increasingly been introducing additional non-native species as a method of controlling the invader. These are predators or parasites (or parasitoids) of the invader species, and they are called “biocontrol agents”.
All in all, we have been underwhelmingly successful in the management of invaders. Â I’ve discussed the horror of the cane toad in Australia, and there are many other failed examples.
This is how big cane toads get. This photo’s not mine though, courtesy of froginmytoilet.blogspot.com
The lady bird beetle (or lady bug, Coccinellidae) was used as early as the late 1800′s as a biocontrol agent of scale insects in citrus crops, and later as a biocontrol agent for mealy-bug infestations.
Lady bird beetle (Hippodamia convergens)
The ladybird lost some of its popularity recently, when the introduced Japanese ladybird beetle started infesting homes in late summer in the northern hemisphere.
My lab studies invasive thistles, for which several biocontrol agents have been introduced. There is the rosette-boring weevil Trichosirocalus horridus (also, what a great name, right?):
Trichosirocalus horridus, a biocontrol weevil of thistles. They are very tiny…only a couple of millimeters long. You see how large the thistle spines look in comparison.
The thistle tortoise beetle:
Thistle Tortoise Beetle (Cassida rubiginosa)
And the other weevil Rhinocyllus conicus, which lays its eggs on the flower head. Its larvae bore into the capitulum (flower head) and destroy seeds:
Rhinocyllus conicus, the lesser of two weevils?
These biocontrol agents vary in effectiveness, but none has successfully suppressed the spread of the thistles. Introducing these organisms also brings about the risk that they will start attacking native thistles (which they have).
So biocontrol is a tricky subject. Although it has had some success in the past, it is extremely difficult to predict the impact of introducing a species, even one which you believe will help control a pest.
It is really a complex issue. Often science has good intention and finds out too late the ramifications. I have really been interested in the parasitic Phorid fly now infecting honeybees. Did they find any relationship to the flies used on ants in Texas?
It is complex, for sure. The phorid flies attacking honeybees are cousins to the ones used to control fire ants. The fire ant biocontrols are Pseudacteon tricuspisand P. curvatus, while the one attacking honeybees isApocephalus borealis. So they are not congeneric, but they share a family. Anyway, the phorid attack on honeybees has no relation to the biocontrol of fire ants, which is a relief!
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Thank you. One less mistake made.
That kid is thrilled to have a cane toad. The toad is not so sure. I watched a documentary once on a similar topic where a crop was introduced to biocontrol a weed which caused a mutation then another crop was introduced to biocontrol that one with another consequence and then… by this time I was thinking, ‘Why not just stop now?’ It is interesting work and must be tempting to do, but I guess nature can react unpredictably to science.
It’s true…things are so unpredictable. We understand so little and the interactions are so complex! But sometimes we are desperate. The more specialised the biocontrol agent is to the pest, the better, but there are no guarantees in the field!
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Introducing non native controls is a VERY delicate issue. Seeing the plant material that has been introduced in years past that now crowd out natives makes me upset. We live in the land of Kudzu. Biocontrol agents…whoa…delicate balance.
Sometimes it seems like the only option! The best plan (or the unreachable ideal) is to find something so specific to the host/pest that it cannot conceivably spread to others. Nonetheless, even with trials in the field we are continually surprised by nature.
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there was an old lady who swallowed a fly
I don’t know why she swallowed the fly.
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