Effective biological control of an invasive mealybug pest enhances root yield in cassava
Insects provide critical ecosystem services to humanity, including biological control of pests. Particularly for invasive pests, biological control constitutes an environmentally sound and cost-effective management option. Following its 2008 invasion of Southeast Asia, biological control was implemented against the cassava mealybug Phenacoccus manihoti (Hemiptera: Pseudococcidae) through the introduction and subsequent release of the host-specific parasitoid Anagyrus lopezi (Hymenoptera: Encyrtidae) in Thailand. In this study, we quantify yield benefits of mealybug biological control in Thailand’s cassava crop by using two different types of manipulative field trials: i.e., ‘physical exclusion’ cage trials and field-level ‘chemical exclusion’ assays. In cage trials with two popular cassava varieties, root yield and total dry matter (or ‘biological yield’) were a respective 4.0–4.2 times and 3.5–3.9 times higher in the presence of biological control. Extrapolating results from cage trials, biological control thus ensured an approximate yield gain of 5.3–10.0 T/ha for either variety. Under chemical exclusion trials, P. manihoti populations attained levels of 3266 ± 1021 cumulative mealybug-days (CMD) over a 10-month time period, and no longer impact yields. Moreover, under effective P. manihoti control, both root yield and biological yield increased with season-long CMD measures, and pest management interventions-including insecticide sprays-led to notable reductions in yield. This study is the first to show how biological control effectively downgrades the globally invasive P. manihoti to non-economic status and restores yields in Thailand’s cassava crop. Our work emphasizes the economic value of biological control, reveals how current P. manihoti populations do not necessarily cause yield penalties, and underlines the central importance of nature-based approaches in intensifying global agricultural production.
KeywordsBiological control Biodiversity Sustainable intensification Food security Ecosystem services Natural enemies
This manuscript is the result of fully collaborative research, with trials jointly conceptualized, defined and executed by Thai counterparts and CIAT personnel. We would like to thank Dr. Sutkhet Nakasathien at Kasetsart University, and Dr. Prapit Wongtiem and senior administrators at the Thai Department of Agriculture for facilitating this work and encouraging graduate students and junior research staff. We are also grateful to Dr. James Cock for revising an earlier draft of the manuscript. This initiative was conducted as part of an EC-funded, IFAD-managed, CIAT-executed programme (CIAT-EGC-60-1000004285), while additional funding was also provided through the CGIAR-wide Research Program on Roots, Tubers and Banana (CRP-RTB).
This study was conducted as part of an EC-funded, IFAD-managed, CIAT-executed programme (CIAT-EGC-60-1000004285), while additional funding was provided through the CGIAR-wide Research Program on Roots, Tubers and Banana (CRP-RTB).
Compliance with ethical standards
Conflict of interest
All authors declare that there are no conflicts of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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