Use of the parasitoid Mastrus Ridens to control the codling moth
The codling moth is considered a major bioaggressor in apple orchards due to its wide geographic distribution, the economic impact of the damage caused, the significant use of insecticides it entails, and the limited available control methods.
In this context, this article aims to evaluate the potential of using a pre-pupal parasitoid of the genus Mastrus (Hymenoptera: Ichneumonidae). This approach, currently at the experimental stage, is conducted and supported by a public research team specialized in biological control research and development (R&D), in collaboration with technical institutes and agricultural professional organizations capable of ensuring the effectiveness and deployment of control methods.
Description
The Codling Moth Issue
The codling moth (Cydia pomonella) is a nocturnal moth whose larva (apple worm) attacks the fruits of the apple tree, pear tree, walnut tree, and other fruit trees. It originates from Central Asia. With climate change, increasing pressure from this bioaggressor is observed. In France, 2 to 4 generations of this pest can be observed depending on the region and the temperatures reached during the year. Across the entire French territory, control of C. pomonella on apple trees alone accounts for 30 to 40% of insecticide treatments.
Among the available biocontrol methods, much hope has so far been placed on sexual confusion and the use of granulovirus, two methods that have limitations. A diversification of biocontrol methods is therefore necessary to complement existing management methods and potentially limit the possibilities of their circumvention by the codling moth, particularly in less protected areas (organic farming, gardens, and wild apple trees).
A Promising Solution
INRAe, seeking alternative solutions to existing methods to control this pest, is studying the feasibility of acclimating a new beneficial insect, a micro-wasp parasitoid of the codling moth.
Biological control by acclimation consists of introducing an exotic beneficial insect so that it establishes itself in a territory and sustainably controls the targeted populations. Once established, the beneficial insect must be able to disperse naturally and control the pest throughout a territory (cultivated areas, wild environments, etc.).[1]
Description of the Beneficial Insect
Origin
Mastrus ridens is a Hymenoptera (micro-wasp) of the family Ichneumonidae.
A specific parasitoid of the codling moth, discovered in the 1990s in Kazakhstan.[2]
As an exotic parasitoid, releases are currently only experimental and under the supervision of INRAe (see the section Participate in the project) which currently holds release authorizations (see the section Regulations).
Application
Mode of Action
The adult female of Mastrus ridens lays her eggs on the host larva. It is a gregarious parasitoid, meaning several parasitoid larvae can develop on the same codling moth larva.
Females locate codling moth larvae thanks to aggregation pheromones (pheromones capable of attracting individuals of both sexes) emitted by the larvae when they spin their cocoons. Mastrus ridens attacks exclusively the pre-pupal stage of the codling moth, which is also its diapause stage (from which adult moths will emerge the following spring).
M. ridens thus has the ability to parasitize diapausing codling moth larvae (but also non-diapausing cocoons), which could significantly reduce the winter inoculum of this pest. Adult M. ridens are present year-round and females are active as soon as temperatures exceed 15°C. To optimize the chances of establishment of M. ridens, experimental releases are carried out in late summer (from late August to early October), when diapausing larvae are abundant.
Période de présence :
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Life Cycles
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Towards a Success Story?
Experiments Around the World
Following its discovery in Asia, M. ridens was deliberately introduced into apple and walnut orchards in California (1998), Argentina (2003), Chile (2006), New Zealand (2013), and Australia (2015)[3][4][5]. In all these countries, this parasitoid has successfully established itself[6]. Parasitism rates of over 30% up to 70% in overwintering cocoons have been observed in California, thus maintaining codling moth populations below damage thresholds.[7][2]
These introductions carried out in other countries suggest a promising path, since M. ridens ensures parasitism levels far higher than those achieved by local species present in France.[8]
Experience APAL Australia:
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“BIOCCYD-Mastrus” in France
In 2019, BIOCCYD-Mastrus, a similar project led by the Sophia Agrobiotech Institute Unit of INRAe and funded by FranceAgriMer, was initiated with 23 release sites of M. ridens (19 dessert apple orchards, 3 cider orchards, and 1 walnut orchard) and, in 2022, the experimental setup includes 57 release sites located in the northwest and southeast of France.
The project coordination is ensured by relays participating in all operations of characterization, releases, recaptures, and population monitoring in each production basin: the French Institute of Cider Productions (Orne), the INRAe Experimental Horticultural Unit (Maine-et-Loire), and the CTIFL La Morinière (Indre-et-Loire) for the regions Brittany, Normandy, and Pays de la Loire; the INRAe Integrated Horticultural Production Unit (Avignon), the GRCETA Basse-Durance, and the La Pugère Experimental Station for the PACA region and the Rhône valley; the CTIFL / SudExpé (Hérault) for the Occitanie region; and the CTIFL / SENURA and the Coopenoix cooperative for releases on walnuts in the Isère valley.[8]
Project Objectives
The objective of the trial is to expand the range of available biocontrol methods and products, by implementing a practice of biological control against the codling moth by acclimating M. ridens.
This operation aims at the sustainable establishment of the beneficial insect and should thus allow at least partial durable control of the pest in production orchards but also in codling moth reservoir areas (abandoned orchards, wild trees, gardens, etc.).
Participate in the Project
(see Contact Information)
Experimental introduction operations of Mastrus ridens in the field are carried out with the research teams participating in the project.
 Information to be considered by participants |
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Field efficacy evaluation results (pre- and post-introduction monitoring) aim to characterize various parameters and measures:
These observations are made on diapausing larvae that may be located on control sites up to 2 km from release zones. |
Practices During the Transition Period
Practice Adaptations
There are several means to control the codling moth:
- Synthetic insecticides are mostly incompatible with the beneficial insect. Resistance cases have been reported since the late 1980s for some. Most chemical insecticide families are currently affected by resistance phenomena.
- Moreover, biological insecticides are often used alongside this practice; see the compatibility of biological insecticides with the beneficial insect in the table below (compatibility tests are currently underway):
| Active Ingredient | Type of Biocontrol | Commercial Product | Compatibility with the beneficial insect Mastrus ridens |
| Granulovirus | Microorganism | Carpodelia, Carpof, Granulovirusine 2000 | 
|
| Pheromones | Chemical mediator | Checkmate CM XL, CIDETRACK-OFM, Confuse |
|
| Bacillus thuringiensis (kurstaki) | Microorganism | Costar WG, Dipel DF, Scutello DF, Bactura DF, Lepinox Plus, Delfin |
|
| Nettle Manure | Natural substance | - |
|
| Sucrose | Natural substance | - |
|
| Spinosad | Biopesticide | Conserve, Syneïs bait | 
|
Other practices are compatible to compensate for the lost efficacy due to the ban on contact insecticides such as Spinosad.
- Sexual confusion, although the rapid reproduction of the codling moth reduces its effectiveness.
- The granulovirus, although resistance cases against some isolates are known[9].
- Nets can be a high investment. Moreover, their impact on the presence and dispersion of M. ridens remains to be evaluated.
The potential impact of other methods on M. ridens (nematodes for example) remains to be evaluated.
Therefore, all these techniques need to be combined, to achieve effective Integrated Pest Management (IPM).
Monitoring the Establishment of the Beneficial Insect
Alongside these measures, it is important to continue monitoring pest and beneficial insect populations after releases using trap bands.
To monitor the establishment of M. ridens, two types of corrugated cardboard bands are used, fixed around the trunks or branches of apple trees:
- 2 cm wide sentinel bands, with diapausing larvae, deployed in the field in spring and summer to characterize the seasonal activity of M. ridens.
- 10 cm wide empty bands, attached to tree trunks in early July (and left in the field until October) to trap diapausing larvae of C. pomonella potentially parasitized by M. ridens.
It is important to emphasize that during participation in these trials, these trap bands must not be burned, as this could destabilize the M. ridens population and make monitoring its establishment more difficult. Studies are currently underway to explore the possibility of implementing an augmentorium system[11].
Regulations
Authorization for Introduction
Following the opinion issued by ANSES, the Order of May 9, 2017 issued by the Ministries of Agriculture and Environment authorizes INRAe to introduce Mastrus ridens into the environment.
Evaluation Criteria
Environmental Impact
Biodiversity
Beneficial organisms: Mastrus ridens has been studied as a biological control agent against the codling moth, and laboratory tests have shown it to be highly host-specific. It has no effect on other economic or environmental aspects. This suggests that the beneficial insect population does not represent a risk[6][12].
Pests: Shows low attraction to non-target hosts, ensuring the highest level of parasitism on C. pomonella. Fifteen species of Lepidoptera have already been tested as potential non-target hosts for M. ridens. Among these, the leafroller (Argyroploce chlorosaris), the brown-headed leafroller (Ctenopseustis obliquana), the lesser appleworm (G. prunivora) and the gorse pod moth (C. succedana) have occasionally been attacked and supported the development of some larvae to adulthood. However, the average number of attacks and M. ridens larvae reaching maturity on these non-target hosts was significantly lower than on the codling moth for all tested species[6][12].
Based on all these tests, the risks of unintended effects appear very low, and the risk/benefit balance clearly favors the introduction of M. ridens.
Agronomic Impact
Productivity
An increase in yield is expected due to reduced production losses caused by caterpillar damage.
Economic Impact
Short Term
The service is provided "free of charge" to farmers who participate in the initiative. Following introductions, field monitoring will need to be conducted for several years to precisely characterize the parasitoid's establishment and dispersal capabilities.
Given the acclimation time of parasitoids, farmers will need to use existing biological approaches such as sexual pheromones and granuloviruses (see Practice adaptations), which constitutes the main program expense to accommodate the new biological agent tested in the region.
Long term
M. ridens allows for the consideration of a more or less significant reduction in currently used control methods (chemical control in particular) with expected benefits in terms of treatment costs, human health, and environmental preservation. Synergies can even be hoped for between this classical biological control strategy and other practices (single-plot netting, mating disruption, etc...) [6].
Social impact
Workload
Working time may be slightly increased due to several factors that must be carried out to optimize control: implementation of other control practices, maintenance and monitoring, discussion with researchers/other farmers.
The evaluation of the dispersion of the auxiliary and the effectiveness of this method are carried out by research institute staff, which does not represent any additional workload for the farmer.
Participate in the research project?
Nicolas Borowiec's research team at INRAe offers interested producers (especially in apples and walnuts) to join the project. If this applies to you, click here to participate:
References
- ↑ Borowiec N. & Sforza R (2020). Biological control by acclimation. In: Biocontrol, elements for agroecological crop protection - Chapter 3. Quae Editions
- ↑ 2.0 2.1 Mills N, Selecting effective parasitoids for biological control introductions: Codling moth as a case study, Biol Control 34:274–282 (2005).
- ↑ Mills N, CLASSICAL BIOLOGICAL CONTROL OF CODLING MOTH: THE CALIFORNIA EXPERIENCE, 6.
- ↑ Tortosa, O. E., Carmona, A., Martinez, E., Manzano, P., & Giardina, M. (2014). Release and establishment of Mastrus ridens (Hymenoptera: Ichneumonidae) for the control of Cydia pomonella (Lepidoptera: Tortricidae) in Mendoza, Argentina. Revista de la Sociedad Entomológica Argentina, 73(3-4), 109-119.
- ↑ Charles JG, Sandanayaka WRM, Walker JTS, Shaw PW, Chhagan A, Cole LM, et al., Establishment and seasonal activity in New Zealand of Mastrus ridens, a gregarious ectoparasitoid of codling moth Cydia pomonella, BioControl 64:291–301 (2019).
- ↑ 6.0 6.1 6.2 6.3 Muru, D. et al. An exotic parasitoid to fight the codling moth. (2018).
- ↑ Horticultural Unit - MASTRUS RIDENS [Internet]. [cited 2021 Nov 17]. Available from: https://www6.angers-nantes.inrae.fr/horti/Dispositifs-d-experimentations/MASTRUS-RIDENS
- ↑ 8.0 8.1 Borowiec, N. et al. An exotic parasitoid against the codling moth. Phytoma 739, 39–43 (2020).
- ↑ Siegwart M et al. The codling moth resists the virus granulosis. Phytoma 738 (2020)
- ↑ Davis, V.A. & Sandanayaka, Manoharie & Charles, John. (2018). Parasitoids associated with codling moths (Cydia pomonella) in apple growing regions in New Zealand.
- ↑ Deguine JP et al. The augmentorium, an agroecological crop protection tool. Design and evaluation in peasant environments on Reunion Island. Cahiers Agricultures 20 (2011)
- ↑ 12.0 12.1 Borowiec N. et al. Introduction dossier for the parasitoid hymenopteran Mastrus ridens. INRAe, 34pp.
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