Warmer weather perfect for pests to thrive

AgResearch scientist and pasture entomologist Colin Ferguson, of Invermay, says a warmer climate, even by a couple of degrees, is likely to mean more pests moving from the north to our region. Photo: SRL Archives

Yvonne O'Hara continues her series of articles on climate change -  part of a project developed with funding from Aotearoa/New Zealand Science Journalism Fund.

Insects are going to love any projected warmer climates and will be more inclined to procreate, says AgResearch scientist and pasture entomologist Colin Ferguson.

''Many insect pests we have got for the main part are driven by temperature, so the warmer it is, the quicker they grow, the more generations they can get through in a year and the more damage they can cause,'' Mr Ferguson said.

He said they included aphids, the diamondback moth and the Argentine stem weevil, all of which were introduced species.

''We also have lots of insects which are potential agriculture pests in the South but aren't yet.

''They don't have the opportunity, currently, to build up enough numbers to cause damage [because of the temperatures].

''Probably those which could be of concern include the clover/lucerne fleas.

''They are here at the moment but not considered a major pest.''

He said another pest farmers might encounter was the Tasmanian grass grub.

It liked warm, dry conditions and was found for the first time in Otago, at Cromwell, last summer.

Large flights were reported this spring.

''The fodder beet moth is also in the region and while they are not seen in huge numbers, that could easily change.''

He said the Argentine stem weevil had already started to respond to changes in climate during the past 20 years.

''We used to get one complete generation a year 20 years ago, and now that has increased to two generations.''

He said one female could be responsible for 60 larvae but with two generations, and if each female insect (half will be males) produced 60 larvae, that was 1800 insects in just one year.

Waikato temperatures mean farmers typically have to deal with three generations a year and there, one female can give rise to 27,000 larvae between spring and autumn.

''While some, such as grass grub, may not show much change, others will.

''We could probably expect porina to start behaving more like their North Island cousins with moths flying in autumn rather than spring and summer.

''We can expect to see a more significant spread [to this region] from further north.

''So we may see pests like black field cricket, red-headed cock chafer and plantain moths appear here.''

He said more species were expected to establish from Australia.

''We have some native species of army worms, which aren't much of a problem, and we have some exotic species, which further north occasionally can be, but there are several species we don't have and don't want.

''With some, when there are enough of them, they will literally move across pasture like a seething front.''

He said southern pastures often supported high numbers of native insects but that could change.

''Introduced species could push native species out of their ecological niches.

''If it got a little bit warmer, some aphid species would respond quickly, and within a season could cause problems.

''In some ways, we have to wait to see what turns up. We won't be able to predict everything.''

He said a complicating factor in dealing with increased pest pressure was the scrutiny insecticides were facing.
Southern Rural Life