Managing weta damage to vines through an understanding of their food, habitat preferences, and the policy environment

Abstract

Insects cause major crop losses in New Zealand horticulture production, through either direct plant damage or by vectoring disease Pugh (2013). As a result, they are one of the greatest risks to NZ producing high quality horticulture crops (Gurnsey et al. 2005). The main method employed to reduce pest damage in NZ horticulture crops is the application of synthetic pesticides (Gurnsey et al. 2005). However, there are a number of negative consequences associated with pesticide use, including non–target animal death (Casida & Quistad 1998) and customer dissatisfaction. Therefore, research is essential to find ecological control methods to manage insect damage in NZ primary industries. On NZ wineries, insect herbivory is mostly conducted by invasive and common insects. However, in the Awatere Valley, herbivory on newly-formed vine buds is caused by the endemic and iconic weta species H. promontorius (Joanne Brady, personal communication, March 5th, 2014). Due to weta having iconic status in New Zealand, there is an extra incentive to find more ecological measures to reduce their effect on wine production. The objective of my thesis was to assess both ecological control methods and policy strategies to mitigate H. promontorius damage on vines, and to conserve the endemic insect. This approach was developed because of the iconic status of weta and because of the increasing knowledge of the negative effects of pesticide use. Under controlled laboratory conditions, I investigated laboratory maintenance effects of diet, container size, and habitat on the relative growth rate (RGR) and survival of H. promontorius. Weta fed a higher protein diet had a significantly higher RGR after 56 days than weta fed a low protein diet. Although death rate between treatments was not significant, there was a tendency for higher protein diets to have a lower death rate than weta fed low protein diets. Container size significantly impacted weta percentage survival when comparing 400 ml to two litre containers; however, there was no significance between two and one litre containers. Habitat factors proved to be non-significant. Further research should investigate all three factors over longer time frames to confirm treatment implications on weta performance. To test for potential trap crop plants, choice tests were conducted in a controlled temperature room. Both amount of food eaten, and whether food was eaten or not, were much higher for broad bean (Vicia faba Linneaus), in the Leaf Trial compared to phacelia (Phacelia distans Benths), buckwheat (Fagopyrum esculentum Moench), and alyssum (Lobularia maritime Linnaeus). In addition, broad bean was the only non-vine plant to be eaten significantly more than a vine plant in a bioassay. Furthermore, the amount of broad bean eaten when paired with a vine bud was significantly more than other non-vine treatments paired with a vine bud. The next step to justify broad bean as a trap crop would be to run trap crop trials on vineyards. To investigate the distribution of H. promontorius on vineyards, transects were constructed on different vineyards. Location of burrows and soil penetration resistance were significantly correlated with H. promontorius density. Testing with the same methods needs to be run over consecutive years to compare conditions and to be confident in the results. Evaluating potential policies to conserve H. promontorius on vineyards entailed literature reviews, and interviewing vineyard managers, including some who had previously dealt with controlling other iconic NZ pest species. Results concluded that conservation within businesses relies heavily on government input and businesses having conservation embedded into the company’s culture. The next stage would be to trial suggested policies in an applied setting.