Fight against a mi­grant in­va­sion

Kapi-Mana News - - NEWS - By JIM CHIPP

Aotearoa’s his­tory is lit­tered with mi­grant in­va­sions over-run­ning na­tives, in­clud­ing rab­bits, fer­rets, pos­sums, gorse and pakeha.

Science can’t do much to reestab­lish the pre-em­i­nence of in­dige­nous hu­mans, but it may of­fer some de­fence against other un­wel­come mi­grants.

Greater Welling­ton re­gional coun­cil’s biose­cu­rity staff have suc­cess­fully in­tro­duced 13 in­sect, rust and fungi species which feed on pest plants and have plans for more.

The coun­cil’s en­vi­ron­men­tal well­be­ing com­mit­tee was told last month that the coun­cil was tak­ing the lead on the in­tro­duc­tion of Hon­shu white ad­mi­ral but­ter­fly to con­trol the spread of Ja­panese hon­ey­suckle.

The hon­ey­suckle is an in­va­sive weed caus­ing con­cern through­out New Zealand.

Greater Welling­ton biose­cu­rity of­fi­cer Harvey Phillips said a group sup­ported by most of New Zealand’s re­gional coun­cils col­lec­tively de­cided when a pest plant had be­come so well-en­trenched that phys­i­cal or chem­i­cal mea­sures could not bring it un­der con­trol and some­thing else was needed.

The Greater Welling­ton coun­cil has ap­plied to in­tro­duce the Hon­shu white ad­mi­ral, but the Hori­zons coun­cil would cham­pion an agent to con­trol field horse­tail.

‘‘Prob­lem plants are iden­ti­fied. Land­care then look at a sur­vey to see if there is any­thing on that land the can be used.’’

Test­ing was vir­tu­ally com­plete and the Hon­shu but­ter­fly was ex­pected to be in­tro­duced last next sum­mer, proved the En­vi­ron­men­tal Pro­tec­tion Au­thor­ity ap­proved it.

Im­ported plants are of­ten in­nocu­ous in their home­land so Land­care goes back to there to find an agent that nat­u­rally con­trols its spread, and brings sam­ples back to a se­cure en­vi­ron­ment in New Zealand, Mr Phillips said.

Rusts and fungi were tested in Auck­land, where there were fa­cil­i­ties to con­tain spores and in­sects are tested at Lin­coln, first to en­sure they stay on the host plant and then to see if they at­tacked closely-re­lated na­tive plants.

The im­ported pest Old Man’s Beard is closely-re­lated to na­tive clema­tis, so most of its nat­u­ral con­trol agents would also at­tack New Zealand na­tives.

‘‘ The safety is­sue is huge be­cause once you’ve got it out there work­ing it won’t stop, re­gard­less of later de­ci­sions,’’ Mr Phillips said. ‘‘We can’t af­ford any mis­takes.’’ An in­sect in cap­tiv­ity may stay with its pre­ferred food source, ig­nor­ing sim­i­lar nearby na­tives but in the wild, when its pre­ferred plant is un­avail­able, may turn to na­tive al­ter­na­tives.

‘‘Even those lit­tle jumps are a bit scary,’’ Mr Phillips said. Not all species jumps are bad. Green this­tle beetle was in­tro­duced to con­trol Cal­i­for­nia this­tle, but it was known to also feed on Scotch this­tle and var­ie­gated this­tles, both in­tro­duced pest plants.

‘‘That was ac­cept­able,’’ Mr Phillips said.

‘‘Luck­ily, there are no close­lyre­lated na­tive plants to this­tles.’’

Trades­cantia, com­monly known by the less po­lit­i­cally- cor­rect name wan­der­ing Jew, proved a prob­lem.

Green this­tle bee­tles were suc­cess­fully tested but there was a prob­lem.

‘‘The first in­sects they brought in had a gut bug.’’ he said.

‘‘They were al­lowed to in­tro­duce the beetle but not the gut bug.’’

The gut bug would have been able to trans­fer to na­tive bee­tles, and it took years to breed a beetle free of it.

‘‘I can’t em­pha­sise enough the safety pre­cau­tions Land­care take to make sure we don’t put an in­sect out that’s go­ing to at­tack or­na­men­tal, eco­nomic or na­tive plants.’’ Mr Phillips said.

When the agent is ap­proved Mr Phillips finds a suit­able site to es­tab­lish a breed­ing pop­u­la­tion and then re­dis­tributes it through­out the re­gion.

Broom shoot moth was re­leased on re­serve land near Porirua last De­cem­ber to con­trol trades­cantia.

Green this­tle beetle was re­leased in Ran­gi­tu­mau, Wairarapa in 2009 to help landown­ers con­trol Cal­i­for­nian this­tle.

Gas­tar­beiter: A Hon­shu white ad­mi­ral but­ter­fly at work.

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