Continental-scale suppression of an invasive pest by a host-specific parasitoid heralds a new era for arthropod biological control

Abstract

Biological control constitutes one of the world’s prime ecosystems services, and can provide long-term and broad-scale suppression of invasive pests, weeds and pathogens in both natural and agricultural environments. Following (very few) widely-documented historic cases that led to sizeable environmental up-sets, the discipline of insect biological control has -over the past three decades- gone through much-needed reform. Now, by deliberately taking into account the ecological risks associated with insect biological control, immense environmental and societal benefits can be gained. In this study, we document and analyze a rare, successful case of biological control against the invasive mealybug, Phenacoccus manihoti (Hemiptera: Pseudococcidae) which invaded Southeast Asia in 2008, where it caused substantial crop losses and triggered 2- to 3-fold surges in agricultural commodity prices. In 2009, the host-specific parasitoid Anagyrus lopezi (Hymenoptera: Encyrtidae) was released in Thailand and subsequently introduced into neighboring Asian countries. Drawing upon continental-scale insect surveys, multi-year population studies and (field-level) experimental assays, we show how A. lopezi attained intermediate to high parasitism rates across diverse agro-ecological contexts. Driving mealybug populations below non-damaging levels at a continental scale, A. lopezi allowed yield recoveries up to 10.0 t/ha and provided biological control services worth several hundred dollars per ha (at local farm-gate prices) in Asia’s 4-million ha cassava crop. Our work provides lessons to invasion science and crop protection worldwide, heralds a new era for insect biological control, and highlights its potentially large socio-economic benefits to agricultural sustainability in the face of a debilitating invasive pest. In times of unrelenting insect invasions, surging pesticide use and accelerating (invertebrate) biodiversity loss across the globe, this study unequivocally demonstrates how biological control – as a pure public good – constitutes a powerful, cost-effective and environmentally-responsible solution for invasive species mitigation.

Biological control protects tropical forests

“…Where A. lopezi was present, mealybug abundance was negatively associated with A. lopezi parasitism (ANOVA, F 1,84= 12.615, p= 0.001; Fig. 1; 18 ).…”

“…Insects were surveyed in 549 cassava fields in Myanmar, Thailand, Lao PDR, Cambodia, Viet Nam and southern China, from early 2014 until mid-2015, using standard protocols (see 18 ). Briefly, 8-10 month old fields in the main cassava-growing provinces of each country were selected with assistance from local plant health authorities, with sites located at least 1 km apart and within easy reach by vehicle.…”

“…Parasitism levels of A. lopezi (per tip and per site) were calculated. Next, for sites where A. lopezi was found, we analyzed field-level P. manihoti abundance with A. lopezi parasitism rate with linear regression (see also 18 ). Variables were log-transformed to meet assumptions of normality and homoscedasticity, and all statistical analyses were conducted using SPSS (PASW Statistics 18).…”

“…These wasps were released across Thailand from mid-2010 onward, and were subsequently introduced into Lao PDR, Cambodia and Viet Nam (2011-2013). They established successfully and suppressed mealybug populations across the region 18 . This restored yields by 5.3-10.0 tonnes/ha (as assessed through manipulative assays), and helped stabilize the trade in cassava root, starch and substitute commodities (i.e., maize, wheat, potato) 15 .…”

¿Estamos perdiendo de vista el control biológico de insectos en el ciberespacio?

“…Next, similar to Proulx et al (2014) and Cha and Stow (2015), we examined Google Trends time series of search hits from 2008 to 2018, to track online public interest in a recent CB case. More specifically, we centred on the 2008 invasion of the cassava mealybug, P. manihoti (Homoptera: Pseudococcidae) in Southeast Asia, and the ensuing 2009 introduction of the effective, host-specific A. lopezi in Thailand and neighbouring countries for its control (i.e., Winotai et al, 2010;Wyckhuys et al, 2014;Wyckhuys et al, 2018b). We used the weekly search volume for the terms "Phenacoccus manihoti" and "Anagyrus lopezi" in Google Trends as indicative of changes in global online public interest.…”