Chrysolina quadrigemina
Greater St Johns Wort beetle at Watson, ACT
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| Chrysolina quadrigemina | MichaelMulvaney | 26 Oct 2021 | |
| Unverified | MPW | 26 Oct 2021 |
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User's notes
Dark Shiny / Iridescent Beetles gathering on Notorious Weed St John's Wort. In a localised area of around 100sq m only, these Beetles are Abundant, but Not elsewhere nearby. St John's Wort has Catastrophic Abundance this year, many 1000's of plants and very dense / sq m. If this is a herbivore ? Beetle for this weed, it seems to have minimal effect, as the Plants are very healthy and growing rapidly under ideal growth conditions this year.
3 comments
26 Oct 2021
This beetle was an introduced biological control for St Johns Wort. I remember reading a paper on its efficacy which said that it worked best in forested areas where St John's Wort was already struggling - but was overall pretty poor - but better than nothing
1 Nov 2021
quotes from a NZ Biological Control of Weeds Book:
" the beetles have a summer hibernation (aestivation)
and become more difficult to see as they hide
away. ...
Once the beetles come out of their summer
hibernation they begin to lay eggs. Each female
can lay several hundred eggs and you may see
these on the undersides of the leaves and in the
growing tips mostly during autumn and winter.
...Both the adults and the larvae defoliate the
plants so heavily that flowering and seed
production is suppressed. The larvae can
destroy new spring growth almost as soon as it
is produced. Heavily defoliated plants are
smaller and weaker, and their chances of
survival are lower."
So don't spray St John's Wort where you have seen a lot of beetles!
" the beetles have a summer hibernation (aestivation)
and become more difficult to see as they hide
away. ...
Once the beetles come out of their summer
hibernation they begin to lay eggs. Each female
can lay several hundred eggs and you may see
these on the undersides of the leaves and in the
growing tips mostly during autumn and winter.
...Both the adults and the larvae defoliate the
plants so heavily that flowering and seed
production is suppressed. The larvae can
destroy new spring growth almost as soon as it
is produced. Heavily defoliated plants are
smaller and weaker, and their chances of
survival are lower."
So don't spray St John's Wort where you have seen a lot of beetles!
1 Nov 2021
OK, Good One ! will monitor this Beetle population at the Fair, to see how they affect the St John's Wort in coming weeks.
Sofar no sign of any Herbivore impact on the Dreaded Wort...🤔🙄
Sofar no sign of any Herbivore impact on the Dreaded Wort...🤔🙄
Location information
- Coordinates 149.170833-35.224444
- Maps The Fair, Watson
- Places Watson, ACT
Sighting information
- 101 - 1,000 Abundance
- 23 Oct 2021 06:01 PM Recorded on
- MPW Recorded by
- St John's Wort Associated plant
- 12mm to 25mm Animal size
- Unknown Gender
Collections
- MPW Canberra & Southern Tablelands NatureMapr Chrysolina quadrigemina Leaf beetles (Chrysomelidae) Beetles (Coleoptera) Insects
Species information
- Chrysolina quadrigemina Scientific name
- Greater St Johns Wort beetle Common name
- Not Sensitive
- Exotic
- Non-invasive or negligible
- Up to 1025.94m Recorded at altitude
- External link More information
Record quality
Quality score
5 / 7
- Images or audio
- More than one media file
- Verified by an expert moderator
- Description
- Additional attributes
- Nearby sighting(s) of same species
- GPS evidence of location