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Integrated management of ground wētā (Orthoptera: Anostostomatidae) in Marlborough vineyards

Nboyine, Jerry Asalma
Fields of Research
ANZSRC::070603 Horticultural Crop Protection (Pests, Diseases and Weeds) , ANZSRC::070604 Oenology and Viticulture
The intensification of agriculture has led to monocultures of high-yielding plant species/cultivars over large areas of land. This provides abundant resources for insects which feed on those monocultural species, elevating them to the status of econmic pests. In the Marlborough region, New Zealand, the conversion of native vegetation in the Awatere Valley to pastures, and in the last 30 years to vineyards, has elevated an endemic orthopteran insect, referred to as wētā (Anostostomatidae) in Maori language, to occasional pest status. This wētā damages vine buds at budburst, consequently reducing yields. Damage is currently managed by tying plastic sleeves around the trunks of vines (Vitis vinifera L.); the sleeves are slippery and deny wētā access to buds. This management approach was adopted, instead of using pesticides, because of the significance of wētā in Maori culture and threats to populations of some wētā species. However, this management technique is labour intensive and costly, and sleeves often need to be repaired/replaced, leading to further costs. They also litter the environment when they become detached from the vines. Hence, this PhD work aimed at developing an ecologically-based integrated management strategy for wētā based on an understanding of the biology and ecology of the species associated with vine damage. A range of laboratory and field experiments were conducted to 1) confirm the identities and number of wētā species damaging vines, 2) wētā biology, densities and distribution in vine and non-vine habitats, 3) the range of plant species in wētā diet, 4) habitat manipulation strategies to mitigate wētā damage and 5) strategies to deter this insect from vineyards. A phylogenetic analysis of sequences obtained from wētā collected from vineyards confirmed that a single species was associated with bud damage. It was identified as Hemiandrus sp. ‘promontorius’ (Johns 2001) using morphological keys. This species is not threatened but has a restricted habitat range. It laid a mean of 55 eggs between March and May, and these hatched after five months. The sex ratio of this wētā was unity. Of three habitats searched, higher numbers of this insect per square meter were found in vines than in either pastures or shrublands. Within vineyards, they were mostly found inhabiting burrows in the bare, moist and less compact soil under vines, with few wētā occupying burrows in the inter-row. A high throughput analysis of DNA sequences from faecal pellets of wētā collected from vineyards showed that this insect feeds on plants from 30 families and 44 genera. Although vines and grasses were the dominant plants in the viticultural landscape studied, dicotyledonous weeds were found to be important components of wētā diet. In terms of management, three under-vine treatments [pea straw mulch (Pisum sativum L.), mussel shells (Perna canaliculus Gmelin, 1791), tick beans (Vicia faba Linn. var. minor (Fab.))] and two inter-row treatments [exisitng ryegrass-dominant vegetation, tick beans] were tested for their efficacy to mitigate wētā damage. Controls comprised vines with plastic sleeves (treated) or no sleeves (untreated), with the existing ryegrass-dominant inter-row vegetation. In this experiment, damage reduction resulted in a 28 and 39% significant yield increase in the under-vine bean and shell treatments respectively, compared to the untreated control. These yield increments were not significantly different from a 30% increment recorded in the sleeve treatment over the untreated control. Apart from mitigating wētā damage, some advantages of the under-vine bean and shell treatments over sleeve treatments include the ability of the beans to habour natural enemies for the control of other vine insect pests; shells conserve moisture and suppresses weed growth under the vines. Endophyte-infected grasses were also tested for their potential to deter wētā from vineyards. Laboratory choice and no-choice experiments demontrated that the loline alkaloids produced by the endophytes in the grasses prevented further feeding by wētā after the initial bite which occurred at the base of their stems. However, this initial bites severed the tillers from the stem and resulted in reduced biomass of endophyte-infected grasses in the no-choice experiment. Results of field experiments from one site also corroborated the potential of these grasses to be used to deter wētā from vineyards. In conclusion, this work proposes a suite of non-pesticidal and sustainable alternatives (shells, under-vine tick beans, endophyte-infected grasses) to mitigate wētā damage in vineyards. These alternatives could either be used alone or together with the current sleeve management approach. Future works could examine combining these strategies into a kind of ‘push-pull’ wētā management strategy, with ‘push’ factors comprising endophyte-infected grasses and shells. ‘Pull’ could comprise strips of non-crop habitats established at the boundaries of vine blocks. Plants in this habitat could consist of tick beans, as well as the shrubs and dicotyledous weeds identified in the insect’s diet.
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