Incorporate parasitism rates when setting thresholds for insecticide use

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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Background information and definitions

This involves monitoring parasitism rates of pests by natural enemies and adjusting thresholds for insecticide use accordingly. Conventional threshold-based insecticide use (such as in integrated management) monitors pest populations or crop damage to schedule insecticide applications, but may not consider the action of natural enemies. Parasitoids can reduce pest populations, but there may be a lag between pest population increase and parasitoid population increase. If pests are killed by insecticides during this lag period, parasitoids may also be killed, preventing the parasitoid population from increasing and limiting the ecosystem service they provide. Monitoring parasitism rates to decide whether or not and when to spray is intended to avoid this and reduce unnecessary use of insecticides.

Study locations

Key messages

Pest damage: One controlled study from New Zealand found using parasitism rates to inform spraying decisions resulted in acceptable levels of crop damage from pests. Effects on natural enemy populations were not monitored.

The crop studied was tomato.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

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.
Study and other actions tested
Referenced paper
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.

Please cite as:

Wright, H.L., Ashpole, J.E., Dicks, L.V., Hutchison, J., McCormack, C.G. & Sutherland, W.J. (2020) Some Aspects of Enhancing Natural Pest Control. Pages 589-612 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK

Where has this evidence come from?

List of journals searched by synopsis

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This Action forms part of the Action Synopsis:

Natural Pest Control

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