Buddleja (also known incorrectly as Buddleia) are wonderful nectar plants which are often recommended for Butterfly gardens. They are named after the Reverend Adam Buddle (1662–1715). There are about a hundred species and they are native to four continents. Unfortunately in New Zealand an introduced Chinese species Buddleja davidii has become an invasive weed.
The buddleja leaf weevil, Cleopus japonicus, was released in New Zealand by Scion in 2006 as a biological control agent for Buddleja davidii, following approval from the Environmental Risk Management Authority (ERMA) as it was known then. Scion is the trading name for New Zealand Forest Research Institute Limited, a New Zealand Crown Research Institute (CRI). The weevil has spread over 50 km from some release sites and is rapidly increasing in population density and distribution.
The weevil lays its eggs on the leaves of buddleia bushes. The eggs hatch and grow into a yellowish grub up to 5mm in length (like a small maggot), which eats away at the leaves, defoliating the plant, much like monarch caterpillars on swan plants. However, in this case, the grub stunts the buddleia’s growth and can even eventually kill it. The grub pupates in a cocoon on the leaf, eventually emerging as the adult weevil that can fly to a new plant to mate.
Although the target is wild Buddleja davidii, the weevils also attack other Buddleja species popular with butterfly gardens.
- Buddleia weevil laying waste to weeds: http://www.scionresearch.com
- Cleopus japonicus: releases and distribution of the buddleia biological control agent in New Zealand. M.C. Watson, T.M. Withers and M. Heaphy. New Zealand Plant Protection 64: 155-159 (2011). http://www.nzpps.org/journal/64/nzpp_641550.pdf
- Application for Release of a leaf weevil for biological control of buddleia. Forest Research http://www.epa.govt.nz/Documents/NOR02001-application.pdf
I’ve noticed that my Buddleja Silver Anniversary is not being attacked. The release application noted that Cleopus japonicus “could attack other Buddleja species in New Zealand, but not B. salvifolia” http://www.epa.govt.nz/Documents/NOR02001-application.pdf
Buddleja davidii, and Cleopus japonicus are native to Sichuan, China. Buddleja salvifolia however is native to Africa. It turns out Buddleja Silver Anniversary is a crossing of Buddleja crispa from Sichuan, China and Buddleja loricata from Africa. So it is probably the African Buddleja in its parentage that gives Silver Anniversary its apparent immunity.
I have sprayed my affected plants with Yates Mavrik which I bought at my local supermarket. Hopefully that gets rid of the weevils.
The Mavrik seems to have worked. The grubs have changed from yellow to brown and new leaves are appearing all over the browned-off parts.
Bother, my Buddleja Silver Anniversary is now being attacked. So while it seemed less attractive to the weevil than the other nearby buddlejas, it doesn’t have immunity after all.
At least there is a solution in Mavrik. It is very low toxicity to non-invertebrates, and it wont bother bees if you spray at dusk after the bees have finished work for the day. By the next day it has dried and won’t affect them at all. I can’t see any reason why the same wouldn’t be true for butterflies. Just don’t plant your buddlejas next to your swanplants and watch out for spray drift.