A leaf eating weevil released by Ensis to help control buddleia (Buddleja davidii) appears to be establishing well at trial sites in North Island forests.
Although it is early days, scientists see the performace of cleopus as promising.
Ensis scientists closely monitoring the spread of cleopus report that the characteristic feeding damage has been easy to find, and weevils have already spread for more than 100 metres at one site.
The first release of the Chinese weevil (Cleopus japonicus) was marked by an official event in the Whakarewarewa forest in Rotorua last spring, after many years of research.
Since then cleopus has been released onto buddleia at four other sites: Kinleith, Lake Taupo Forests, the Esk Forest in Hawkes Bay and Rawhiti Forest Farm near Ohope.
Ensis entomologist Michelle Watson says the primary purpose of these releases is to get the biological control agent established in the New Zealand environment.
The initial release sites were selected to maximise the climatic range cleopus might encounter in areas with buddleia in New Zealand.
“Early signs are that cleopus is doing well at all sites with several generations recorded, which means the insect is breeding successfully.
“Feeding damage to buddleia plants within the central release area is considerable, with cleopus feeding on both new and old foliage,” Michelle explains.
“When biological control agents such as this are released against a weed, the numbers are so small that it is often hard to find them again. Cleopus has surprised us all.”
Michelle says while the omens are good for the establishment of cleopus, the weevil has yet to survive its first New Zealand winter.
“Even if cleopus survives the winter we won’t know for some years whether populations will grow large enough to reduce buddleia growth and survival sufficently to benefit the forests, but we are cautiously optimistic,” Michelle says.
Buddleia imposes huge costs on the New Zealand forestry industry, through chemical control and reducing the early growth of trees.
The fast growth and ability of buddleia to colonise bare ground, outcompeting other species, has allowed it to become a serious pest plant in both plantations forest and natural areas.
“It is hoped that cleopus, will help to reduce these costs and also provide some control in natural areas where access is difficult,” says Michelle.
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