Study

An adjustable action threshold using larval parasitism of Helicoverpa armigera (Lepidoptera: Noctuidae) in IPM for processing tomatoes

  • Published source details Walker G.P., Herman T.J.B., Kale A.J. & Wallace A.R. (2010) An adjustable action threshold using larval parasitism of Helicoverpa armigera (Lepidoptera: Noctuidae) in IPM for processing tomatoes. Biological Control, 52, 30-36

Actions

This study is summarised as evidence for the following.

Action Category

Incorporate parasitism rates when setting thresholds for insecticide use

Action Link
Natural Pest Control

Use pesticides only when pests or crop damage reach threshold levels

Action Link
Natural Pest Control
  1. Incorporate parasitism rates when setting thresholds for insecticide use

    A controlled study in 2000-2002 in Hawke’s Bay, New Zealand (Walker et al. 2010) found that tomato Solanum lycopersicum damage from cotton bollworm Helicoverpa armigera larvae did not exceed the commercially acceptable level of 5% on 16 of 17 occasions when treatment decisions were based on parasitism-adjusted pest thresholds. Only 1.2-5.5% of tomatoes were damaged in 11 fields where decisions to not spray crops used thresholds accounting for parasitism (damage exceeded the acceptable 5% level in only one field), and 3.0-3.4% were damaged in two sprayed fields where conventional thresholds (using pest but not parasitism levels) were used. Tomato damage averaged 3.9-7.1% in three unsprayed fields where cotton bollworm numbers exceeded parasitism-adjusted threshold levels. Treatment decisions were made for 22 fields which met or exceeded a conventional threshold of one cotton bollworm larvae/plant, suggesting spraying was necessary. However, in 16 fields and one half-field, crops were only sprayed if bollworm numbers exceeded thresholds adjusted for site-specific parasitism rates (ranging 1-8.3 larvae/plant). Controls included two fields sprayed when only the conventional pest threshold was exceeded, and three fields and one half-field left unsprayed despite exceeding all thresholds. Insecticides included spinosad and Bacillus thuringiensis pesticidal bacteria. Fruit damage was assessed for 40 random plants/field.

  2. Use pesticides only when pests or crop damage reach threshold levels

    A trial in 2000-2002 in Hawke’s Bay, New Zealand (Walker et al. 2010) found that tomato Solanum lycopersicum damage did not exceed the commercially acceptable level of 5% at harvest on 16 of 17 occasions when decisions to spray were made using thresholds of cotton bollworm Helicoverpa armigera larvae abundance. On average, 0.8-5.5% of tomatoes were damaged in treated fields compared with 3.9-7.1% in unsprayed fields (where thresholds were also exceeded). The decision to not treat crops while maintaining < 5% damage was correct 10 out of 11 times. Treatment decisions were made for 22 fields which all met or exceeded a conventional threshold of one larvae/plant. However, in 16 fields and one half-field, spraying only took place if larvae numbers exceeded an adjustable threshold accounting for site-specific parasitism rates (see 'Incorporate parasitism rates when setting thresholds for insecticide use'). Thresholds varied from 1-8.3 larvae/plant. Insecticides included spinosad or Bacillus thuringiensis pesticidal bacteria. Fruit damage was assessed for 40 random plants/field. Three fields and one half-field were left unsprayed to assess crop damage without treatment, but the effects of spraying with and without a pest threshold approach were not compared. Effects on natural enemies were not presented.

Output references

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, terrestrial mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 18

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.


Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape Programme Red List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Bern wood Supporting Conservation Leaders National Biodiversity Network Sustainability Dashboard Frog Life The international journey of Conservation - Oryx British trust for ornithology Cool Farm Alliance UNEP AWFA Butterfly Conservation People trust for endangered species Vincet Wildlife Trust