Invertebrate Monitoring

 

Guava moth

The guava moth (Coscinoptycha improbana), a native of Australia, has a voracious appetite for the fruit of many Northland trees – feijoa in particular. They were first found in Kaitaia in 1997. Since then the Council has been involved in monitoring the spread and distribution of guava moth in Northland. Pheromone traps have been placed around the region to trap the adult moth. In 2004 it was found that guava moth are quite well distributed throughout Northland, so the role of the council has been reduced to investigation of sightings outside known infestation areas. The Council has also produced a pamphlet to assist identification and management of quava moth, which is available on the Regional Council website as a pdf under publications.

Tropical grass webworm

Tropical grass web worm.

The tropical grass webworm (Herpetogramma licarsisalis) has caused severe pasture damage in the Far North. In the last major outbreak in 1999, five hectares of paddocks were completely chewed out in less than 48 hours. 1500 caterpillars per square metre were recorded, equivalent to 15 million per hectare.

A monitoring programme is actioned each summer to assess number of larvae and adults in Far North properties to pre-empt a heavy infestation of webworm. This gives a window of opportunity to warn farmers of an imminent outbreak and instigate management practices to lessen the impact. Monitoring is undertaken over summer (December-April) on the Aupouri Peninsula where previous major infestations have occurred. Pheromone traps are installed to capture any adult moths. Weekly counts at four sites are undertaken of webworm larvae in 25 quadrants randomly over half a hectare to determine the number of larvae per square metre.

Detailed weather data, including rainfall and hourly temperature recordings, is collected from an electronic data logger. Reports on the potential risk of pasture damage is issued to farmers on a regular basis, recorded in the Kaitaia-based ‘Northland Age' newspaper and NRC website.

Over the 2005-06 summer period 452 moths were caught in pheromone traps, mostly during March when the weather was warm, moist, and humid. A peak of 38 larvae/m2 was recorded at one site during April. Fortunately, there was not a serious infestation of webworm in 2005-2006, despite favourable weather conditions later in the summer. This was probably due to dry conditions in early summer. Similar monitoring will continue next financial year.

Gum leaf skeletoniser

The gum leaf skeletoniser (Uraba lugens) is an Australian insect that damages, mostly gum trees (Eucalyptus sp.), by eating the foliage. It is now widespread in the greater Auckland region. In collaboration with HortResearch, Biosecurity NZ, and Ensis, the Council assists in monitoring the distribution and spread in Northland.

In March and April 2006 60 pheromone traps where deployed on eucalyptus trees at high risk sites throughout the region. Of the 60 traps only four had any moths which resembled the gum leaf skeletoniser; these are currently being formally identified. To date the gum leaf skeletoniser has not been identified in Northland from this programme. This monitoring is not routine but will be carried out again in the future as required.

Pest ants

Pest ants, particularly the Argentine ant (Linepithema humile), have become a prominent pest issue throughout Northland in recent years as population densities have increased, particularly in urban areas. Existing records of pest ants were clustered around urban centres as that is where most complaints are generated. This summer the Regional Council, in conjunction with the Department of Conservation, monitored sites around significant ecological areas to determine presence/absence. The monitoring had two aims: to help direct policy development and to initiate control work if feasible in these important areas.

A total of 345 bait stations were set in the 14 sites surveyed. Argentine ants were only found on one bait station; close to the golf course in Ahipara. Survey results are summarised in the table below.

Site	Date	Number of baits stations	Argentine ants identified
1. Mimiwhangata -carpark/beachfront	20/12/05	40	0
2. Bland Bay	5/1/06	35	0
	9/1/06	35	0
3. Te Paki - DOC Field Centre	16/1/06	30	0
4. Cape Reinga	17/1/06	15	0
5. Taupotupotu Bay	17/1/06	15	0
6. Waitiki Landing	17/1/06	20	0
7. Te Hapua	18/1/06	20	0
8. Spirits Bay	18/1/06	20	0
9. Ahipara Coast	3/2/06	18	1
10. Ahipara Gumfields	3/2/06	22	0
11. Mimiwhangata - campground	7/2/06	20	0
12. Mimiwhangata - Molly's Bush	7/2/06	20	0
13. Houhora Head	10/2/06	20	0
14. Kaimaumau Village	10/2/06	15	0
TOTAL		345	1

 

The results of this survey suggest that Argentine ants were not present at most of the sites surveyed. However, the natural rate of spread of Argentine ant colonies is thought to be less that 200m/annum, therefore it is probable that very small populations may be missed. The design of the survey aimed to target known preferred habitats of Argentine ants at the survey sites and vector pathways (e.g. car parking areas, farm equipment) in an effort to pick up small incursions of ants. Despite this methodology, Argentine ants were confirmed at the settlement within the surveyed area at Bland Bay within a few weeks of the survey. Although the settlement is over 1km from the area targeted for protection, it was included in the survey as the presence of people act as a very high risk for vector ant incursion.

Future monitoring will include surveillance monitoring that targets vector points (entry points) in to Northland such as ports and marina areas and significant ecological and economic areas where the potential impacts from a pest ant incursion are high.