Unsung heroes: fixing multifaceted sustainability challenges through insect biological control

Highlights

• Biological control (BC) is a desirable, nature-based alternative to synthetic pesticides.

• Beneficial insects restore ecological regulation of invaded agro-ecosystems.

• By lifting crop yields, BC resolves malnutrition, rural poverty and economic hardship.

• Trans-disciplinary research can elucidate net positive social-ecological outcomes.

Insects are indispensable actors within global agri-food systems and ensure the delivery of myriad ecosystem services. A progressive decline in insect numbers — as inflicted by habitat loss, pollution or intensive agriculture — can jeopardize a sustained provisioning of those services. Though we routinely disregard how insects help meet multiple sustainable development challenges, a gradual insect decline can have grave, long-lasting consequences. Here, we describe how insect-mediated biological control not only defuses invasive pests and can reconstitute crop productivity, but equally delivers other positive social-ecological outcomes. Drawing upon the pan-tropical invasion of the cassava mealybug and its ensuing suppression by the monophagous parasitoid Anagyrus lopezi, we illuminate how biological control contributes to food security, poverty alleviation, human wellbeing and environmental preservation. Trans-disciplinary research and ‘systems thinking’ are needed to maximize the potential of these biodiversity-driven interventions, and thus reap the net positive spin-offs insects provide for farmers, the environment and human society.

Introduction

Insect biodiversity underpins sustainable food systems and secures a delivery of myriad ecosystem services such as pollination, nutrient cycling or biological pest control [1,2^••]. In conventional agro-production systems, as typified by genetically uniform monocultures, ‘locked-in’ chemical dependencies and heavy mechanization, these biodiversity-based ecosystem services have steadily degraded [3, 4, 5]. Amongst others, a unidimensional focus on yield gain has deepened farmers’ perceived need for petroleum-derived inputs, while downplaying the role of ecosystem service-providing organisms such as beneficial insects. This is further aggravated by scant, empirically derived information on insects’ contribution to ecosystem service delivery in agricultural settings [6]. Parallel to those trends, the unrelenting appearance of new invasive pests puts mounting pressure on agro-ecosystems, negatively impacting biodiversity, ecosystem functioning and primary productivity while often triggering environmentally disruptive responses.

Not only are the monetary impacts of invasive species infrequently assessed [7], there also is a deficient understanding of how they affect sustainability currencies for example, environmental integrity or societal wellbeing. A failure to conduct these assessments in an unbiased, comprehensive fashion can obscure biodiversity-driven mitigation measures [8,9] and ultimately favor unsuitable practices [10^•]. In light of the above, today’s entomologists need to examine the multi-faceted benefits of biodiversity-mediated tools for invasive species mitigation. Doing so in the tropics is particularly rewarding, as this part of the world is bound to bear the brunt of global environmental change and its highly biodiverse ecosystems tend to be managed by some of the world’s poorest and most vulnerable people [7,11].

Insect biological control (BC) entails the scientifically guided conservation, augmentation or introduction of beneficial organisms for the management of (either native or invasive) crop pests, pathogens or weeds [12,13]. The judicious selection and ensuing release of non-native species for the mitigation of invasive pests (so-called ‘classical biological control’) has a long and rich history typified by hundreds of success stories [14]. Though few ill-advised interventions in the mid-1900s did result in unintended ecological impacts [15], modern-day biological control has become a desirable, environmentally sound and near ‘tailor-made’ approach for invasive pest control. One widely acclaimed BC endeavor is the 1980’s campaign against the invasive mealybug Phenacoccus manihoti (Hemiptera: Pseudococcidae) on African cassava Manihot esculenta (Malpighiales: Euphorbiaceae), using the neotropical parasitoid Anagyrus lopezi (Hymenoptera: Encyrtidae) [16]. Through an internationally coordinated initiative by the Consultative Group of International Agricultural Research (CGIAR) and Centre for Agriculture and Bioscience International (CABI), this host-specific wasp was collected in Paraguay by the late Anthony C. Bellotti, screened under quarantine conditions in the UK and released in western Africa during the early 1980s. Laboratory rearing, field testing and follow-up introductions over 1981–1995 permitted the establishment of A. lopezi in 26 African countries, causing substantial reductions in P. manihoti population levels and securing a near-total recovery of local crop yields.

In 2008, P. manihoti made its accidental arrival in Southeast Asia (Figure 1), threatening the viability of a thriving cassava industry and prompting an internationally endorsed, preventative use of neonicotinoid insecticides over extensive areas. Yet, in 2009, Thailand’s Royal Government equally opted to mobilize A. lopezi. From 2010 onward, parasitoids were mass-reared and released across Southeast Asia, successfully established at a regional level and suppressed invasive P. manihoti populations [17]. Attaining average parasitism levels of 30.0 ± 24.0% (n = 110), A. lopezi amply surpassed established thresholds for successful biological control, drove down mealybug numbers and restored crop yields [17]. Though most local farmers remained unaware of the exact identity, ecology and dispersal mode of either crop antagonist or beneficial [18], BC provided a cost-free, self-propelling means of pest suppression for millions of Asian smallholder families. Here, we illuminate several important yet rarely quantified outcomes of this successful case of biological control and frame them within the broader context of the United Nations Sustainable Development Goals (UN-SDG) (Figure 2).