Harnessing the Power of Natural Enemies: Biological Control in Almond Tree IPM

Introduction

Almond (Prunus dulcis (Mill.) D.A. Webb) production faces significant challenges from pests such as carob moth (Ectomyelois ceratoniae) and Carpophilus beetles (Carpophilus spp.), which threaten yield and marketability (Agriculture Victoria Research, 2020). Integrated Pest Management (IPM) offers a sustainable framework to address these challenges by combining biological, cultural, and chemical strategies. Central to this approach is biological control, which leverages natural enemies to suppress pest populations while minimizing environmental harm (Wyckhuys et al., 2013). This article synthesizes current research on the integration of biological control into almond IPM, emphasizing its role in enhancing orchard resilience and sustainability.

Figure 1. Almond Orchard

Principles of IPM in Almond Production

IPM in almonds is guided by five core principles: monitoring, economic thresholds, prevention, integrated tactics, and evaluation (Figure 2; Khun et al., 2020). Regular monitoring ensures accurate pest identification and population assessment, enabling timely interventions only when pest densities exceed economic thresholds (Gullan & Cranston, 2014). Preventative measures, such as selecting resistant cultivars and optimizing irrigation, reduce pest establishment (Khalsa, 2018). Chemical controls are deployed judiciously to preserve natural enemies, highlighting the synergy between biological and chemical methods (Khun et al., 2021).

Figure 2. Five principles guiding IPM in Almonds 

Biological Control: Mechanisms and Applications

Biological control utilizes predators, parasitoids, and pathogens to suppress pest populations. In Australian almond orchards, predatory mites, ladybird beetles, and thrips (Figure 3) contribute to pest suppression, though their efficacy depends on habitat management (Agriculture Victoria Research, 2020).

Figure 3. Biological control mechanism in Almond

Source: https://www.sacvalleyorchards.com/almonds/insects-mites/hull-split-spray-tight-fiscal-year/

Conservation of Natural Enemies

Habitat diversification, such as planting floral strips or maintaining weed borders, enhances natural enemy abundance by providing nectar and pollen resources (Wyckhuys et al., 2013). Herbaceous strips in almond orchards sustain parasitoid populations, improving control of lepidopteran pests (Wyckhuys et al., 2013).

Figure 4a,b. a. healthy almond seeds, b. infected almond seeds

Source: https://wcngg.com/ and Zalom et al. (2017)

Entomopathogenic Fungi (EPF)

Fungal pathogens like Beauveria bassiana and Metarhizium spp. show promise against Carpophilus beetles (Figure 5). Lab trials demonstrate 70–90% larval mortality when beetles are exposed to B. bassiana-treated surfaces (Boston et al., 2020). Autodissemination techniques, where pests transfer fungal spores to conspecifics, are being explored to target cryptic pests within mummy nuts (Khun et al., 2021).

Figure 5. Entomopathogenic Fungi 

Source: https://www.queenslandcountrylife.com.au/story/7476913/almonds-look-to-fungi-as-ally-in-beetle-fight/

Augmentative and Classical Approaches

While conservation strategies dominate, augmentative releases of commercially reared parasitoids (e.g., Trichogramma wasps) are under investigation for carob moth control (Agriculture Victoria Research, 2020). Due to stringent biosecurity regulations, classical biocontrol (introducing non-native natural enemies) remains limited (Hort Innovation, 2023).

Key Almond Pests and Biocontrol Strategies

Carob Moth (Ectomyelois ceratoniae)

This polyphagous pest causes kernel damage, particularly in poorly managed orchards (Figure 6). Mating disruption pheromones and habitat manipulation to conserve Copidosoma spp. parasitoids have reduced larval infestations by 40–60% in California (Zalom et al., 2017).

Figure 6. Adult Carob Moth (Ectomyelois ceratoniae)

Carpophilus Beetle (Carpophilus spp.)

Carpophilus beetles evade detection during post-harvest inspections, posing export risks (Figure 7). Attract-and-kill systems using fungal-laced lures have suppressed populations by 50% in field trials (Boston et al., 2020). Orchard sanitation, including mummy nut removal, disrupts breeding sites and complements biocontrol (Hossain, 2018).

Figure 7. Carpophilus Beetle

Challenges in Implementing Biological Control

While biological control in almond orchards holds significant promise for sustainable pest management, it faces several challenges. A fundamental hurdle lies in the complexity of ecological and behavioral processes that underpin the effectiveness of biological control agents. Biocontrol programs may yield unsuccessful results if these processes are not thoroughly understood before implementation (Veres et al., 2020).

Pesticide Interactions and Their Impact on Natural Enemies

One significant challenge stems from the potential pesticide disruption of natural enemy populations. Historically, almond pest management in California heavily relied on broad-spectrum organophosphate insecticides, which were detrimental to natural enemy populations. Even with a shift towards more selective insecticides, off-target impacts on beneficial species remain a concern and can hinder the establishment and efficacy of biological control. Understanding the side-effects of pesticides permitted for use in almonds on beneficial arthropods is crucial for minimizing negative impacts on Integrated Pest Management programs (Brodt et al., 2005; Wyckhuys et al., 2013).

Knowledge Gaps in Almond Biocontrol Research

Another key challenge is the need for comprehensive knowledge of pest species and their natural enemies. Developing an effective IPM program with a biocontrol component requires a thorough understanding of pest biology, behavior, and ecology, as well as the identification and activity of their natural enemies within the almond orchard ecosystem (Wyckhuys et al., 2013; Lubanga et al., 2018). Research efforts in Australia have aimed to address these knowledge gaps for major almond pests like carob moth and carpophilus beetle (Agriculture Victoria Research, 2019). Limited data on the ecology of Australian-native natural enemies hinders tailored strategies (Lubanga et al., 2018). Documenting biocontrol activity and management options helps to raise awareness and interest among researchers and growers in developing enhanced orchard management practices. 

Variability in Biopesticide Performance

Variability in the effectiveness of biocontrol programs presents another challenge. Biopesticide programs, in particular, can exhibit inconsistencies in performance. This variability underscores the importance of rigorous laboratory-based bioassays before commencing field trials to ensure growers are not disappointed with unsatisfactory outcomes resulting from poorly planned implementations. Factors such as genetic modification, formulation, and synergistic use with other microbial agents or sub-lethal pesticides are being explored to enhance the virulence and hardiness of fungal pathogens, while optimization of fermentation processes aims to reduce production costs and improve product stability (Wyckhuys et al., 2013; Khun, 2019).

Furthermore, the integration of biocontrol into existing IPM strategies requires careful consideration. While biological control approaches can successfully contribute to pest suppression in modern agricultural systems through effective IPM, their successful implementation relies on a strong foundation of ecological and behavioral understanding (Almond Board of California, 2003).

In Afghanistan, the implementation of biological control faces additional challenges, including restricted knowledge among farmers about agrochemicals and a reliance on conventional chemical pesticides. The development and registration of biological agents as alternatives are relatively recent, with only a few agents registered or pending registration for commercial use. Limited infrastructure and expertise in the production and application of biocontrol agents can also pose significant barriers.

Ensuring grower adoption of IPM practices incorporating biological control requires effective knowledge transfer and demonstration. Engaging producers and processors in developing and implementing IPM systems is crucial to validating the cost-effectiveness of new biocontrol tools and ensuring their practical application. Providing appropriate knowledge, cost-effective management tools, and on-the-ground demonstrations are key to improving the adoption of IPDM in almonds. The reliance on research projects as major producer information sources highlights the need for effective extension publications and events to broaden knowledge transfer.

Case Studies: Successes in IPM Integration

California’s Transition to Sustainable IPM

California almond growers reduced organophosphate use by 80% through monitoring programs and selective insecticides, enabling natural enemy resurgence (Brodt et al., 2005). PCAs provide site-specific advice on integrating biocontrol with cultural practices (Gott & Coyle, 2019). Reliance on chemical controls persists due to perceived reliability. Education through Pest Control Advisors (PCAs) has improved IPM adoption in California (Brodt et al., 2005).

Australia’s AL16009 Project

Australia's AL16009 Project addressed the escalating kernel damage in almonds due to insect pests by aiming to develop an integrated pest management (IPM) program (Madge et al., 2022). This initiative focused on improving orchard hygiene, developing new attract-and-kill technologies for carpophilus beetle and carob moth, and identifying IPM-compatible pesticide options (Madge et al., 2022). Field surveys identified 12 native predator species, including Orius bugs, which prey on moth eggs (Agriculture Victoria Research, 2020). The project significantly progressed in developing a more attractive lure for carpophilus beetles (Madge et al., 2022). Furthermore, it emphasized the importance of understanding pest species and their natural enemies (Lubanga et al., 2018). The project actively engaged with the almond industry through various knowledge transfer activities, contributing to the reduction of pest and disease damage (Madge et al., 2022).

Future Directions

Advancements in microbial genomics and precision agriculture offer opportunities to refine biocontrol. For example, CRISPR-edited EPF strains with enhanced virulence could target pests without harming pollinators (Yousuf et al., 2022). Additionally, AI-driven monitoring systems may improve pest prediction and natural enemy deployment (CAST, 2003).

Conclusion

Biological control is integral to sustainable almond production, reducing reliance on chemicals while preserving ecosystem health. However, successful implementation necessitates a deep understanding of ecological interactions, careful integration with other pest management tactics, mitigation of pesticide impacts on beneficial species, and effective engagement with the almond industry to ensure knowledge transfer and adoption of these environmentally sound practices.

References

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